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The albinism of the feral Asinara white donkeys ( Equus asinus ) is determined by a missense mutation in a highly conserved position of the tyrosinase ( TYR ) gene deduced protein

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A feral donkey population (Equus asinus), living in the Asinara National Park (an island north-west of Sardinia, Italy), includes a unique white albino donkey subpopulation or colour morph that is a major attraction of this park. Disrupting mutations in the tyrosinase (TYR) gene are known to cause recessive albinisms in humans (oculocutaneous albinism Type 1; OCA1) and other species. In this study, we analysed the donkey TYR gene as a strong candidate to identify the causative mutation of the albinism of these donkeys. The TYR gene was sequenced from 13 donkeys (seven Asinara white albino and six coloured animals). Seven single nucleotide polymorphisms were identified. A missense mutation (c.604C>G; p.His202Asp) in a highly conserved amino acid position (even across kingdoms), which disrupts the first copper-binding site (CuA) of functional protein, was identified in the homozygous condition (G/G or D/D) in all Asinara white albino donkeys and in the albino son of a trio (the grey parents had genotype C/G or H/D), supporting the recessive mode of inheritance of this mutation. Genotyping 82 donkeys confirmed that Asinara albino donkeys had genotype G/G whereas all other coloured donkeys had genotype C/C or C/G. Across-population association between the c.604C>G genotypes and the albino coat colour was highly significant (P = 6.17E−18). The identification of the causative mutation of the albinism in the Asinara white donkeys might open new perspectives to study the dynamics of this putative deleterious allele in a feral population and to manage this interesting animal genetic resource.
Geographical position of the Asinara island, phenotypic details of white Asinara donkeys and the causative mutation determining their albinism. (a) Geographical location of the Asinara island. (b) Asinara white albino donkey. (c) A close-up of the depigmented eye of an Asinara white albino donkey. (d) Recessive Mendelian inheritance of the albino phenotype demonstrated in a trio. Two grey parents (with heterozygous genotype H/D at the p.His202Asp site or C/G in the nucleotide sequence at the c.604C>G nucleotide position, indicated with S, according to the IUPAC nomenclature) gave birth to an albino donkey (D/D genotype or G/G at the nucleotide position). Microsatellite analysis (data not shown) confirmed the relationship among the three donkeys. (e) Alignment of the donkey tyrosinase protein region containing the p.His202Asp substitution with the corresponding region in different species. The grey region indicated with an arrow corresponds to the position of the p.His202Asp substitution in donkeys (H2A position in the CuA site). The other arrow indicates the histidine of the H3A position in the CuA site (the H1A position is not included in this alignment). Protein accession numbers for the sequences used in the alignment are as follows: Equus caballus, F6YIA2; Homo sapiens, P14679; Mus musculus, P11344; Bos taurus, Q8MIU0; Oryctolagus cuniculus, G1SYA0; Gallus gallus, P55024; Xenopus laevis, F7CL37; Danio rerio, F1QDZ4; Ipomoea batatas, Q9MB14; Neurospora crassa, P00440; Bacillus megaterium, B2ZB02. Numbers in the alignments indicate the starting and ending amino acid residues of the corresponding protein.
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SHORT COMMUNICATION
The albinism of the feral Asinara white donkeys (Equus asinus)
is determined by a missense mutation in a highly conserved position
of the tyrosinase (TYR) gene deduced protein
V. J. Utzeri, F. Bertolini, A. Ribani, G. Schiavo, S. Dall’Olio and L. Fontanesi
Department of Agricultural and Food Sciences, Division of Animal Sciences, University of Bologna, Viale Fanin 46, 40127 Bologna, Italy.
Summary A feral donkey population (Equus asinus), living in the Asinara National Park (an island
north-west of Sardinia, Italy), includes a unique white albino donkey subpopulation or
colour morph that is a major attraction of this park. Disrupting mutations in the tyrosinase
(TYR) gene are known to cause recessive albinisms in humans (oculocutaneous albinism
Type 1; OCA1) and other species. In this study, we analysed the donkey TYR gene as a
strong candidate to identify the causative mutation of the albinism of these donkeys. The
TYR gene was sequenced from 13 donkeys (seven Asinara white albino and six coloured
animals). Seven single nucleotide polymorphisms were identified. A missense mutation
(c.604C>G; p.His202Asp) in a highly conserved amino acid position (even across
kingdoms), which disrupts the first copper-binding site (CuA) of functional protein, was
identified in the homozygous condition (G/G or D/D) in all Asinara white albino donkeys
and in the albino son of a trio (the grey parents had genotype C/G or H/D), supporting the
recessive mode of inheritance of this mutation. Genotyping 82 donkeys confirmed that
Asinara albino donkeys had genotype G/G whereas all other coloured donkeys had
genotype C/C or C/G. Across-population association between the c.604C>G genotypes and
the albino coat colour was highly significant (P=6.17E18). The identification of the
causative mutation of the albinism in the Asinara white donkeys might open new
perspectives to study the dynamics of this putative deleterious allele in a feral population
and to manage this interesting animal genetic resource.
Keywords Asinara island, coat colour, deleterious mutation, equid, oculocutaneous
albinism Type 1, pigmentation, population genetics
Asinara (of which one of its middle age etymology seems to
recall the meaning of ‘land of the donkeys’) is a small
Mediterranean island (about 52 km
2
) located closely north-
west of Sardinia (Fig. 1a). This island was inhabited until
1885, at which time it was closed as it became an Italian
quarantine site and subsequently a highly secured prisoner
colony. The island was re-opened to the public in 1999 after
the constitution of the Asinara National Park in 1998
(http://www.parcoasinara.org: Gazzetta Ufficiale della
Repubblica Italiana 1997). Among the species living on
the island, the Asinara white donkey (Fig. 1b) or ‘Asino
dell’Asinara’ (Equus asinus) is the most representative and
peculiar component of the Park’s fauna and is the symbol of
Asinara. The origin of the Asinara white donkeys is
uncertain and based only on legends, from which it is
possible to date the occurrence of the first white donkeys
back to before the closure of the island in the 19th century
(Ministero di Agricoltura, Industria e Commercio 1905;
Vinceti 2007). The Asinara white donkey subpopulation or
colour morph (accounting for ~100120 animals) lives
together with coloured (usually grey) donkeys that can be
attributed to the Asino Sardo population (Pinna et al.
1993). All these donkeys can mate, producing a hybrid
population (whose number of heads is not known). The
whole donkey population of Asinara island (white and
coloured) can be considered a feral population, as no
human direct intervention has been managing these
animals for more than a century (Kugler & Broxham
2014). The white coat coloured animals are also considered
by the Food and Agriculture Organization (Sherf 2000) and
by the register of equine and asinine Italian local breeds
Address for correspondence
L. Fontanesi, Department of Agricultural and Food Sciences, Division of
Animal Sciences, University of Bologna, Viale Fanin 46, 40127 Bologna,
Italy.
E-mail: luca.fontanesi@unibo.it
Accepted for publication 12 October 2015
doi: 10.1111/age.12386
1
©2015 Stichting International Foundation for Animal Genetics
(Ministero delle Politiche Agricole, Alimentari e Forestali
2010) as a donkey breed in critical status.
Despite the uniqueness of the Asinara white donkeys,
only a few authors have investigated this subpopulation. As
far as we know, these animals have been analysed at the
DNA level using microsatellites to evaluate genetic
variability together with other donkey breeds in only two
studies (Cosseddu et al. 2001; Colli et al. 2013). Pinna et al.
(1993) described the Asinara white donkeys at the
morphological level and reported that these animals
resemble those of the Asino Sardo breed in terms of size
and body shape, confirming their genetic closeness deter-
mined by microsatellite markers (Colli et al. 2013). The
differentiating trait is only the complete white coat colour,
lacking pigmentation in the skin, hair, eyelashes and
eyebrows, and eyes that are light blue, as also described
for several forms of human oculocutaneous albinism Type
1A and 1B (OCA1A and OCA1B) defects (e.g. Grønskov
et al. 2007; Fig. 1c). These donkeys have low visual acuity,
and during sunny hours they hide inside the unused
buildings of the prisoner colony. These traits and their
evasive behaviour away from the sun indicate that Asinara
white donkeys are affected by albinism (Pinna et al. 1993).
The albinism in these animals is one of the few cases of this
type of pigmentation defect that is maintained in a wild or
feral vertebrate population (Protas et al. 2006; Xu et al.
2013), as fitness is expected to be lower, especially in a
sunny Mediterranean environment.
In many different species, the albino locus allelic series
(formally identified as the Clocus; Searle 1968) is
determined by mutations in the tyrosinase (TYR) gene that
lead to completely white coat colour and lack of pigmen-
tation in the case of disrupting mutations (Aigner et al.
2000; Oetting 2000; Beermann et al. 2004; Schmutz et al.
2004; Blaszczyk et al. 2005; Imes et al. 2006; Blaszczyk
et al. 2007; Anistoroaei et al. 2008), determining the
recessive callele(s) (Searle 1968). Tyrosinase (EC
1.14.18.1) is the key enzyme involved in the melanogenesis
process in which both melanins (eumelanims and pheome-
lanins) are produced. This enzyme has an active site
(a) (b) (c)
(d) (e)
Figure 1 Geographical position of the Asinara island, phenotypic details of white Asinara donkeys and the causative mutation determining their
albinism. (a) Geographical location of the Asinara island. (b) Asinara white albino donkey. (c) A close-up of the depigmented eye of an Asinara white
albino donkey. (d) Recessive Mendelian inheritance of the albino phenotype demonstrated in a trio. Two grey parents (with heterozygous genotype
H/D at the p.His202Asp site or C/G in the nucleotide sequence at the c.604C>G nucleotide position, indicated with S, according to the IUPAC
nomenclature) gave birth to an albino donkey (D/D genotype or G/G at the nucleotide position). Microsatellite analysis (data not shown) confirmed
the relationship among the three donkeys. (e) Alignment of the donkey tyrosinase protein region containing the p.His202Asp substitution with the
corresponding region in different species. The grey region indicated with an arrow corresponds to the position of the p.His202Asp substitution in
donkeys (H2A position in the CuA site). The other arrow indicates the histidine of the H3A position in the CuA site (the H1A position is not included in
this alignment). Protein accession numbers for the sequences used in the alignment are as follows: Equus caballus, F6YIA2; Homo sapiens, P14679;
Mus musculus, P11344; Bos taurus, Q8MIU0; Oryctolagus cuniculus, G1SYA0; Gallus gallus, P55024; Xenopus laevis, F7CL37; Danio rerio,
F1QDZ4; Ipomoea batatas, Q9MB14; Neurospora crassa, P00440; Bacillus megaterium, B2ZB02. Numbers in the alignments indicate the starting
and ending amino acid residues of the corresponding protein.
©2015 Stichting International Foundation for Animal Genetics, doi: 10.1111/age.12386
Utzeri et al.2
composed of a pair of antiferromagnetically coupled copper
ions, CuA and CuB, which are coordinated by six histidine
residues, three per each copper-binding site (Claus & Decker
2006; Kanteev et al. 2015). Removal of only one of the
copper-binding histidine residues results in loss of the
corresponding copper ion, thereby abolishing enzyme
activity (e.g. Jackman et al. 1991).
In this study, we used a candidate gene approach to
identify the causative mutation of the albinism in Asinara
white donkeys. For this aim, six primer pairs (Table S1)
were designed on the assembled donkey TYR gene
(Bertolini et al. 2015) and used to amplify and sequence
by Sanger and Ion Torrent sequencing technologies (as
described in Fontanesi et al. 2015) all coding exons,
portions of the intronic regions (downstream and
upstream of the exons), 50- and 30- untranslated regions
of the donkey TYR gene in 13 animals of different coat
colours (seven Asinara white donkeys, expected to have
the c/c genotype at the albino locus, and six coloured
donkeys: two grey Asinara donkeys, phenotypically con-
sidered as Asino Sardo donkeys; one Asino Sardo donkey;
one Martina Franca; one Sicilian Grey; and one Ragusano;
EMBL accession numbers LN880531 and LN880532).
Seven single nucleotide polymorphisms (SNPs) were iden-
tified (Table S2). Four SNPs were in exonic regions (three
in exon 1 and one in exon 2), and the remaining
polymorphisms were in intronic regions (two in intron 2
and one in intron 4; Table S2). Of the four missense
mutations, two (c.274G>A or p.Val83Ile in exon 1 and
c.987G>A or p.Glu316Lys in exon 2) were identified only
in the heterozygous condition in one coloured donkey
(Ragusano). The SIFT score (Kumar et al. 2009) indicated
that these two amino acid substitutions are tolerated
(Table S2). For the c.18G>C or p.Leu6Phe mutation, the
genotype for three coloured donkeys of different breeds
(Martina Franca, Grigio Siciliano and Ragusano) was G/G
(L/L), whereas it was heterozygous G/C (L/F) in two grey
donkeys sampled in the Asinara island (resembling Asino
Sardo donkeys) and homozygous C/C (F/F) in the third
grey Asino Sardo donkey sampled in Sardinia. Genotype
C/C or F/F was fixed in all Asinara white albino donkeys
as well (Table S2). SIFT analysis indicated that this
missense mutation is not deleterious (P=0.48). The
second missense mutation (c.604C>G or p.His202Asp;
Fig. 1d), identified only in donkeys from Asinara island
that were homozygous D/D in all sequenced white
donkeys, had a highly significant SIFT score (P<0.001)
supporting the deleterious effect of this substitution
(Table S2).
The amino acid at position 202 of the wild-type TYR
protein is one of the three highly conserved histidine
positions of the first copper-binding site (CuA) of the TYR
catalytic domain (Fig. 1e). This histidine is the second
copper-binding histidine residue within the CuA site (indi-
cated as H2A) that is always present at this position in all
tyrosinase protein sequences available, even across king-
doms (Fig. 1e; Garc
ıa-Borr
on & Solano 2002; Claus &
Decker 2006). The 3D structure of the wild-type and
mutated donkey TYR proteins obtained following the
homology modelling strategy (template protein: PDB entry
4P6R of Bacillus megaterium; Goldfeder et al. 2014) with
MODELLER software (version 9.14; Eswar et al. 2006) con-
firmed the disruptive effect of the p.His202Asp substitution
(Fig. S1).
According to the sequencing data, as grey donkeys
sampled on the Asinara island were heterozygous at the
c.604C>G (p.His202Asp) missense mutation, it was possible
to presume a recessive mode of inheritance of the effect of
the mutated allele, as expected for mutations causing
albinism (Searle 1968). Mendelian recessive inheritance of
this mutation was strengthened by sequencing and
genotyping (Table S1) a trio family sampled on the Asinara
island composed of a grey father (genotype C/G or H/D), a
grey mother (C/G or H/D) and a white albino foal (G/G or D/
D; Fig. 1d).
To further confirm the role of the p.His202Asp substitu-
tion, the c.604C>G mutation was genotyped (Table S1) in a
total of 65 donkeys (including the animals already
sequenced to confirm the sequencing determined genotype)
from eight coloured breeds or populations in addition to 17
feral Asinara white albino donkeys (Table 1). All Asinara
white albino donkeys were homozygous for the mutated
allele. Only four grey Asino Sardo donkeys were heterozy-
gous (three sampled in Asinara National Park, of which the
sequencing of two have already been described and
the third being from a farm in the province of Sassari, in
the north of Sardinia). Considering all genotyped donkeys of
Table 1 Distribution of c.604C>G (p.His202Asp) genotypes obtained
from PCR-RFLP and sequencing analyses among the investigated
breeds.
Donkey breeds/populations No. of donkeys
c.604C>G genotypes
1
C/C C/G G/G
Amiata (coloured) 2 2 ––
Asinara (white albino) 17 –– 17
Asino Sardo (coloured)
2
734
Coloured hybrids (coloured) 13 13 ––
Martina Franca (coloured) 13 13 ––
Pantesco (coloured) 1 1 ––
Ragusano (coloured) 19 19 ––
Romagnolo (coloured) 2 2 ––
Sicilian Grey (coloured) 8 8 ––
Total 82 61 4 17
1
Including also grey donkeys sampled in Asinara island (see text for
details).
2
The number of donkeys with the corresponding genotype is reported.
Genotypes are indicated for the c.604C>G single nucleotide
polymorphism: allele C corresponds to the deduced amino acid histidine
and allele G corresponds to the deduced amino acid aspartic acid for the
missense mutation indicated as protein position (p.His202Asp).
©2015 Stichting International Foundation for Animal Genetics, doi: 10.1111/age.12386
TYR gene mutation and albinism in donkey 3
different breeds and populations and the occurrence of
homozygous G/G (D/D) animals only in albino donkeys,
across-population association between the genotype at the
c.604C>G mutation and the albino phenotype was highly
significant (P=6.17E18; two-tailed chi-squared test).
The phylogenetic tree produced including the five donkey
TYR haplotypes (obtained from the sequenced donkeys using
PHASE program v. 2.1; Stephens et al. 2001) and the horse
sequence (Wade et al. 2009), generated with the UPGMA
method available in MEGA6 software (Tamura et al. 2013),
supported the hypothesis that the albino mutation occurred
in a ‘grey’ haplotype also present in Sardinia donkeys
(Fig. S2). This hypothesis might exclude the legendary origin
of the white donkeys of Asinara that had them deriving from
white Egyptian donkeys imported by Marchese di Mores,
Duke of Asinara Island, in the 19th century, or from a
French shipwreck in the same period (Vinceti 2007).
The isolation of the Asinara donkey population and the
consequent putative high inbreeding level might have been
the causes of the increased frequency of the TYR-mutated
allele in the Asinara island donkey population. The presence
of many small uninhabited tumbledown buildings left over
from previous uses of the island that are used as shelters by
the white donkeys during the sunniest period of the year
and the low activity of these animals during daylight might
reduce the negative effects of this mutation. However, we
cannot be sure whether these hypotheses are sufficient to
explain the conservation of a mutation determining a
potential deleterious effect in a free-living population (Page-
McCaw et al. 2004). We did not investigate whether the
albino TYR haplotype is in linkage disequilibrium with other
variant(s) conferring advantages in a wild, marginal and
harsh environment.
The identification of the causative mutation of the
albinism in the Asinara white donkeys adds a new natural
animal model for human OCA1 defects and might open new
perspectives to study the dynamics of this putative delete-
rious allele in a feral population and to manage this
interesting animal genetic resource that is the symbol of the
Asinara National Park.
Acknowledgements
We thank Giovannatonio Pilo (Asinara National Park
veterinarian), Dr. Guy D’Hallewin (CNR Sassari), Marco
Ghionda (ANAS), Asineria of Gombola, Asinara National
Park personnel for their help during the sampling and
Samuele Bovo and Paolo Manghi (University of Bologna) who
helped with the 3D modelling. This work has been possible
with the collaboration of the Asinara National Park and with
the RFO2014 funds provided by the University of Bologna.
Conflict of interest
The authors declare they have no conflict of interests.
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Supporting information
Additional supporting information may be found in the
online version of this article.
Figure S1 3D modelled structure of the (a) wild type (allele
HHis at position 202) and (b) mutated (allele D Asp at
position 202) TYR proteins in the CuA and CuB copper-
binding sites.
Figure S2 Phylogenetic tree of the donkey TYR gene
haplotypes.
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genotyping.
Table S2 TYR gene polymorphisms and genotypes of the
sequenced donkeys.
©2015 Stichting International Foundation for Animal Genetics, doi: 10.1111/age.12386
TYR gene mutation and albinism in donkey 5
... Though not only melanocytes produce melanin in the animal body, it is also important to point out that the albinism condition in Asinara donkeys is due to a genetic mutation of the TYR Gene encoding for the tyrosinase enzyme (Tyr): partial or total enzymatic inefficiency of tyrosinase can in fact lead to different albino forms, whatever the embryogenic origin of the cells with the ability to synthesize melanin. Melanin is a pigment produced across the animal kingdom, and is responsible for the coloration of the skin, as well as that of hairs, feathers, scales, iris, and mucosa of the mucocutaneous junctions [7]. In humans, different subtypes of albinism are described in the literature and different genes have been identified as being involved. ...
... The genetic mutation encoding for the tyrosinase enzyme (involved in the first steps of the melanogenic process) was fixed through generations, thanks to geographical isolation, favoring an inbreeding phenomenon [20]. The albinism of Asinara white donkeys has been recently identified to be due to a missense mutation in a highly conserved amino acid position (G/G or D/D genotype), diverse from the pigmented phenotype (gray) of the Sardo donkey (C/C or C/G genotype) [7]. Asinara donkeys living on the Asinara island (from which the breed's name originates), a small isle of Sardinia in the Mediterranean Sea, likely branched out of the gray Sardo donkey back in time, in which specimens can carry the gene for this autosomal recessive mutation [21] (Figure 1). ...
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The complete blood cell count (CBC) was screened in a group of 15 donkeys, of which 8 were of Asinara breed (oculocutaneous albinism type 1, OCA1) and 7 of Sardo breed (gray coat). All donkeys were kept under same management and dietary conditions and underwent periodic health monitoring in the month of June 2024, at the peak of the positive photoperiod, at Mediterranean latitudes. One aliquot of whole blood, drawn from each individual into K2-EDTA containing tubes, was analyzed for the complete blood cell count through an automatic analyzer, within two hours of sampling. Data were analyzed and compared by one-way ANOVA, where the breed was an independent variable. All animals appeared clinically healthy, though mild eosinophilia was observed in Sardo donkeys. The red blood cell line showed peculiar traits for Asinara donkeys, which displayed significantly higher circulating red blood cell numbers than gray coat Sardo donkeys (RBC, 5.19 vs. 3.80 1012/mL ± 0.98 pooled-St. Dev, respectively; p = 0.017). RBCs also exhibited a smaller diameter and higher degree of anisocytosis in Asinara donkeys, along with lower hematocrit value, albeit within physiological ranges. Taken all together, such hematological profile depicts a peculiar trait of the red blood cell line in albino donkeys during the positive photoperiod.
... All four reports were from India and from four different species color-aberrant birds that are easily detectable and so gain more public and scientific attention (Zbyryt et al., 2020). Participatory science is also vulnerable to biases through uneven recording or reporting, with greater reporting of individuals or species of special interest (e.g., charismatic or novel species) and uneven spatial coverage of areas that are easily accessible or popular among tourists (Boakes et al., 2016). in Asinara National Park; Utzeri et al., 2015). However, the relatively short documentation period (1.5 years) in comparison to the average malachite kingfisher lifespan (6.3 years; Rose, 2017) suggests it is unlikely there were multiple leucistic individuals. ...
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Color aberrations in birds corresponds with important ecological functions, including thermoregulation and physiological impacts, camouflage and increased predation, and social interactions with conspecifics. Color aberrations in birds have been reported frequently in the scientific literature, but aberrations in many species remain undocumented or understudied. We investigated records of leucism in malachite kingfishers (Corythornis cristatus) from observations of community scientists on iNaturalist and eBird in Uganda. Leucistic kingfishers were only observed within the Queen Elizabeth National Park (QENP), Uganda. When considering all observations of malachite kingfishers that included photographs within the QENP, leucistic individuals accounted for 13.0% and 10.4% of total malachite kingfisher observations within the study area from iNaturalist and eBird, respectively. Leucistic observations were recorded from September 2015 through February 2017, making up 60.0% and 68.2% of observations of malachite kingfishers within the study area from iNaturalist and eBird during that time, respectively. The localized and short documentation period suggests observations represent a single individual, while the high observation rate likely corresponds with collection bias due to the novelty of the individual. Our findings help to better understand the ecological importance and potential consequences for color‐aberrant individuals, although color aberration did not appear to inhibit our subject's ability to find a mate. Our work also highlights how participatory science can promote the documentation of color‐aberrant individuals in wild populations, although it poses challenges when trying to estimate abundance.
... They determined that a 1 bp deletion downstream of the TBX3 gene was responsible for the difference in coat color phenotype, increasing pigmentation in non-Dun donkeys and suggesting a change in coat color during the domestication of wild donkeys into domestic donkeys. A study performed by Utzeri et al. [33] discovered an association between albinism in Asinara white donkeys Animals 2024, 14, 1802 9 of 15 and a specific missense mutation (c.604C>G; p. His202Asp) in the TYR gene. Subsequently, genotyping was conducted on 17 wild Asinara white albino donkeys and 8 colored breeds or populations, totaling 65 donkeys. ...
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Simple Summary Color and body size traits are considered the key parameters influence the economic value of animals. In recent years, advancement in the genetic basis of coat colors in equines has received considerable attention among animal breeders. In addition, coat color plays a significant role in breed identification and selection, as well as animal health and disease. The current review concisely provides information on the role of melanin pigments and key candidate genes associated with coat color phenotypes in equines. Furthermore, the review also highlights the importance of coat color in equine breeding and health. Abstract Variation in coat color among equids has attracted significant interest in genetics and breeding research. The range of colors is primarily determined by the type, concentration, and distribution of melanin pigments, with the balance between eumelanin and pheomelanin influenced by numerous genetic factors. Advances in genomic and sequencing technologies have enabled the identification of several candidate genes that influence coat color, thereby clarifying the genetic basis of these diverse phenotypes. In this review, we concisely categorize coat coloration in horses and donkeys, focusing on the biosynthesis and types of melanin involved in pigmentation. Moreover, we highlight the regulatory roles of some key candidate genes, such as MC1R, TYR, MITF, ASIP, and KIT, in coat color variation. Moreover, the review explores how coat color relates to selective breeding and specific equine diseases, offering valuable insights for developing breeding strategies that enhance both the esthetic and health aspects of equine species.
... Previous research has demonstrated that albinism phenotypes are linked to TYR gene mutations in numerous animals, including mouse [9], cattle [10], rat [11], cat [12], rabbits [13], buffalos [14], chicken [15,16], donkeys [17]. Collectively, the aforementioned investigations have shown that the variations in the TYR gene play a crucial role in the process of melanin formation and the manifestation of the albino phenotype in animals. ...
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Background The TYR gene has been documented to exhibit an association with the dominant white coat color in certain mammalian species. To understand the genotypic profile underlying coat color in Chinese wild-type raccoon dogs and white mutant raccoon dogs, TYR gene was amplified and variations in them were analyzed by DNA sequencing. Results In this study, Sequence analysis revealed that 11 single nucleotide polymorphisms SNPs were detected, and four of them were missense mutations (c.329A > G、c.479A > G、c.1497G > C、c.1523A > C) resulting in amino acid mutations (Cln110Arg, Asn160Ser, Cys1497Phe, His1523Pro). These four SNPs showed a low-to-moderate PIC value ranging from 0 to 0.351. The genotype distribution of all mutations in two raccoon populations of different coat color not reached significant level (p>0.05). Conclusion Overall, the results of this study suggest that TYR gene may lead to a mutation in raccoon dogs fur color to white.
... Compared with bead chips developed using the mainstream Illumina platform and Affymetrix platform, the novel liquid chip has several unique advantages: lower detection cost, flexible adjustment of marker density (1-200k), the ability to add or remove SNP sites at any time and no requirement for a particular sample size (Xu et al., 2020;Zhang et al., 2023). In past years, studies on the genetic basis of donkey coat color variation have been carried out and have revealed polymorphic sites of a few candidate genes such as ASIP, TYR and TBX3 (Abitbol et al., 2015;Utzeri et al., 2016. However, few studies have been conducted at the genome-wide level. ...
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Dezhou donkey is one of the representative local breeds in China, which is mainly divided into two strains: Sanfen and Wutou. There are obvious differences in coat color between the two strains. The former shows light points around the eyes, around the muzzle and under the belly, while the latter is completely solid black. In this study, genome‐wide association analysis was performed for the differences in coat color traits between the Sanfen (n = 97) and Wutou (n = 108) strains using a novel donkey 40K liquid chip developed based on GenoBaits technology, to identify genomic regions and causal genes that could explain this variation. We also used FST and The cross‐population composite likelihood ratio test (XPCLR) analyses to explore selected regions related to coat color differences. We identified one significant region on chromosome 15, with the most significant SNP located within the agouti signaling protein (ASIP) gene. At the same time, both FST and XPCLR methods detected the same selected region on chromosome 15, and ASIP was the gene with the strongest signal. ASIP and melanocortin 1 receptor (MC1R) control the ratio of eumelanin to pheomelanin through their protein activity. They are deeply involved in the process of melanosome organation and melanogenesis, thus affecting mammals’ coat color variation. We used a range of genome‐wide approach to identify the genetic basis of coat color variation in Dezhou donkeys. The results provide a supplement to the color variation study in Chinese donkeys at the genome‐wide level, and preliminarily verified the reliability of the Molbreeding Donkey No. 1 40K liquid chip.
... Specimens with altered color patterns are recorded in all vertebrate groups: mammals (Smírnov 2014;Toledo et al. 2014;Utzeri et al. 2016), birds (van Grouw 2012; Moller et al. 2013), reptiles (de Noronha et al. 2013), amphibians (López and Ghirardi 2011;Toledo et al. 2011) and fish (Lara-Mendoza and Guerra-Jiménez 2018). ...
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Fish populations in environments with a high degree of geographic isolation may be prone to mutations expressed in the phenotypes. These mutations may be related to color pattern, forming leucistic individuals. This work aims to register and to describe possible mechanisms that influence this mutation. Additionally, the study compares other morphometric variations among different populations and leucistic individuals of Heptapterus mustelinus . A total of four leucistic individuals were collected in a small shaded stream, highly segmented by rapids and waterfalls. The biometric analyses showed no significant morphological differences when compared to other populations of the same ecoregion. The selection of leucism may be directly related to the sampled environment, since the leucistic specimens occurred in a shaded stream with dense vegetation cover. Low occurrence of predatory species of fish can be an important point to maintain the characteristic. Consequently, predation may not exert a negative selective pressure on leucistic individuals.
... The Asinara donkey (alternative names include "white donkey" or "albino donkey") is a rare small albino variety (withers from 80 to 105 cm high) of feral donkey with a white coat, unpigmented skin and mucosa and pinkish-blue eyes (Fig. 1). The latter two features are caused by a mutation in the tyrosinase gene (TYR) [18]. It is given the specific name of "Equus africanus asinus var. ...
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abstract: The Asinara donkey is a rare small albino variety of feral donkey listed as ''critical'' by the Food and Agriculture Organization of the United Nations (FAO) and by the Domestic Animal Diversity Information System (DAD-IS) in 2022. The objectives of the present study were to evaluate the reproductive characteristics of healthy male Asinara donkeys through andrological evaluation and testicular echo-color-Doppler examination to assess correlations between testicular blood supply and sperm production and to compare it with horse reproductive characteristics. Eight healthy donkeys and stallions were subjected to semen collection and evaluation, ultrasound and Doppler evaluation of the testicles and serum testosterone determination. The testosterone concentrations in donkeys were 1.42 ± 0.69 ng/ml while in horses were 1.90 ± 0.63 ng/ml within the normal values reported in these species. Horses had greater mean and total testicular volume, semen gel-free volume, and total sperm number than donkeys (P
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Vertebrate pigmentation patterns are amongst the best characterised model systems for studying the genetic basis of adaptive evolution. The wealth of available data on the genetic basis for pigmentation evolution allows for analysis of trends and quantitative testing of evolutionary hypotheses. We employed Gephebase, a database of genetic variants associated with natural and domesticated trait variation, to examine trends in how cis-regulatory and coding mutations contribute to vertebrate pigmentation phenotypes, as well as factors that favour one mutation type over the other. We found that studies with lower ascertainment bias identified higher proportions of cis-regulatory mutations, and that cis-regulatory mutations were more common amongst animals harbouring a higher number of pigment cell classes. We classified pigmentation traits firstly according to their physiological basis and secondly according to whether they affect colour or pattern, and identified that carotenoid-based pigmentation and variation in pattern boundaries are preferentially associated with cis-regulatory change. We also classified genes according to their developmental, cellular, and molecular functions. We found a greater proportion of cis-regulatory mutations in genes implicated in upstream developmental processes compared to those involved in downstream cellular functions, and that ligands were associated with a higher proportion of cis-regulatory mutations than their respective receptors. Based on these trends, we discuss future directions for research in vertebrate pigmentation evolution.
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Abstract While almost half of all mammal species are rodents, records of albinism in free‐ranging rodents are very rare. Australia has a large and diverse assemblage of native rodent species, but there are no records of free‐ranging albino rodents in the published literature. In this study, we aim to improve our understanding of the occurrence of albinism in Australian rodent species by collating contemporary and historic records of this condition and providing an estimate of its frequency. We found 23 records of albinism (i.e., a complete loss of pigmentation), representing eight species, in free‐ranging rodents native to Australia, with the frequency of albinism being generally
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Background Pigment regression is an intriguing phenomenon that can be caused by disorders in melanin metabolism or endocrine regulation, or by autoimmune disorders. Albino animals serve as excellent models for the study of the genetic determination of morphology, particularly the evolution of and molecular mechanisms underlying chromatophore-related diseases in animals and humans. Material and Methods The artificial culture of Andrias davidianus, the largest extant amphibian, is flourishing in China due to the great ecological and economic value of this animal. Approximately 0.1% of individuals express an albino phenotype accompanied by delayed somatic growth and mortality at early developmental stages. In this study, brain and skin transcriptomics were conducted to study the underlying molecular basis of the phenotype. Results The results indicated decreased transcription of genes of melanin synthesis. Interestingly, MHC I isotypes and immune-related pathways accounted for the primary transcriptional differences between groups, suggesting that the albino phenotype represents a systematic immune problem to a far greater extent than a pigmentation defect. Albino individuals exhibited shifted transcription of MHC I isotypes, and the albino-specific isotype was characterized by increased charges and decreased space in the antigen- binding pocket, implying a drastic change in antigen specificity and a potential risk of autoimmune disorders. Conclusion These results suggest an association between the albino phenotype and MHC I variants in A. davidianus, which could serve as a convenient model for vitiligo or other autoimmune diseases.
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Few studies investigated the donkey (Equus asinus) at the whole genome level so far. Here, we sequenced the genome of two male donkeys using a next generation semiconductor based sequencing platform (the Ion Proton sequencer) and compared obtained sequence information with the available donkey draft genome (and its Illumina reads from which it was originated) and with the EquCab2.0 assembly of the horse genome. Moreover, the Ion Torrent Personal Genome Analyzer was used to sequence reduced representation libraries (RRL) obtained from a DNA pool including donkeys of different breeds (Grigio Siciliano, Ragusano and Martina Franca). The number of next generation sequencing reads aligned with the EquCab2.0 horse genome was larger than those aligned with the draft donkey genome. This was due to the larger N50 for contigs and scaffolds of the horse genome. Nucleotide divergence between E. caballus and E. asinus was estimated to be ~ 0.52-0.57%. Regions with low nucleotide divergence were identified in several autosomal chromosomes and in the whole chromosome X. These regions might be evolutionally important in equids. Comparing Y-chromosome regions we identified variants that could be useful to track donkey paternal lineages. Moreover, about 4.8 million of single nucleotide polymorphisms (SNPs) in the donkey genome were identified and annotated combining sequencing data from Ion Proton (whole genome sequencing) and Ion Torrent (RRL) runs with Illumina reads. A higher density of SNPs was present in regions homologous to horse chromosome 12, in which several studies reported a high frequency of copy number variants. The SNPs we identified constitute a first resource useful to describe variability at the population genomic level in E. asinus and to establish monitoring systems for the conservation of donkey genetic resources.
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Tyrosinase is responsible for the two initial enzymatic steps in the conversion of tyrosine to melanin. Many tyrosinase mutations are the leading cause of albinism in humans, and it is a prominent biotechnology and pharmaceutical industry target. Here we present crystal structures that show that both monophenol hydroxylation and diphenol oxidation occur at the same site. It is suggested that concurrent presence of a phenylalanine above the active site and a restricting thioether bond on the histidine coordinating CuA prevent hydroxylation of monophenols by catechol oxidases. Furthermore, a conserved water molecule activated by E195 and N205 is proposed to mediate deprotonation of the monophenol at the active site. Overall, the structures reveal precise steps in the enzymatic catalytic cycle as well as differences between tyrosinases and other type-3 copper enzymes.
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We announce the release of an advanced version of the Molecular Evolutionary Genetics Analysis (MEGA) software, which currently contains facilities for building sequence alignments, inferring phylogenetic histories, and conducting molecular evolutionary analysis. In version 6.0, MEGA now enables the inference of timetrees, as it implements our RelTime method for estimating divergence times for all branching points in a phylogeny. A new Timetree Wizard in MEGA6 facilitates this timetree inference by providing a graphical user interface (GUI) to specify the phylogeny and calibration constraints step-by-step. This version also contains enhanced algorithms to search for the optimal trees under evolutionary criteria and implements a more advanced memory management that can double the size of sequence data sets to which MEGA can be applied. Both GUI and command-line versions of MEGA6 can be downloaded from www.megasoftware.net free of charge.
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... cutaneous albinism type 2: effects of altering intracellular pH and pink-eyed dilution gene expression. ... 37. Rosenmann E, Rosenmann A, Ne&apos;eman Z, Lewin A, Bejarano-Achache I, Blumenfeld A: Prenatal diagnosis of oculocutaneous albinism type I: review and personal ...
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The white tiger, an elusive Bengal tiger (Panthera tigris tigris) variant with white fur and dark stripes, has fascinated humans for centuries ever since its discovery in the jungles of India [1]. Many white tigers in captivity are inbred in order to maintain this autosomal recessive trait [2-5] and consequently suffer some health problems, leading to the controversial speculation that the white tiger mutation is perhaps a genetic defect [6]. However, the genetic basis of this phenotype remains unknown. Here, we conducted genome-wide association mapping with restriction-site-associated DNA sequencing (RAD-seq) in a pedigree of 16 captive tigers segregating at the putative white locus, followed by whole-genome sequencing (WGS) of the three parents. Validation in 130 unrelated tigers identified the causative mutation to be an amino acid change (A477V) in the transporter protein SLC45A2. Three-dimensional homology modeling suggests that the substitution may partially block the transporter channel cavity and thus affect melanogenesis. We demonstrate the feasibility of combining RAD-seq and WGS to rapidly map exotic variants in nonmodel organisms. Our results identify the basis of the longstanding white tiger mystery as the same gene underlying color variation in human, horse, and chicken and highlight its significance as part of the species' natural polymorphism that is viable in the wild.
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We report a high-quality draft sequence of the genome of the horse (Equus caballus). The genome is relatively repetitive but has little segmental duplication. Chromosomes appear to have undergone few historical rearrangements: 53% of equine chromosomes show conserved synteny to a single human chromosome. Equine chromosome 11 is shown to have an evolutionary new centromere devoid of centromeric satellite DNA, suggesting that centromeric function may arise before satellite repeat accumulation. Linkage disequilibrium, showing the influences of early domestication of large herds of female horses, is intermediate in length between dog and human, and there is long-range haplotype sharing among breeds.
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Tyrosinases are metalloenzymes belonging to the type-3 copper protein family which contain two copper ions in the active site. They are found in various prokaryotes as well as in plants, fungi, arthropods, and mammals and are responsible for pigmentation, wound healing, radiation protection and primary immune response. Tyrosinases perform two sequential enzymatic reactions, hydroxylation of monophenols and oxidation of diphenols to form quinones which polymerize spontaneously to melanin. Two other members of this family are catechol oxidases which are prevalent mainly in plants and perform only the second oxidation step, and hemocyanins which lack enzymatic activity and are oxygen carriers. In the last decade, several structures of plant and bacterial tyrosinases were determined, some with substrates or inhibitors, highlighting features and residues which are important for copper uptake and catalysis. This review summarizes the updated information on structure-function correlations in tyrosinases along with comparison to other type-3 copper proteins. This article is protected by copyright. All rights reserved. © 2015 The Protein Society.