[Show abstract][Hide abstract] ABSTRACT: HP1 proteins are conserved components of eukaryotic constitutive heterochromatin. In mammals, there are three genes that encode HP1-like proteins, termed HP1alpha, HP1beta and HP1gamma, which have a high degree of homology This paper describes for the first time, to our knowledge, the physiological function of HP1gamma using a gene-targeted mouse.
While targeting the Cbx3 gene (encoding the HP1gamma protein) with a conditional targeting vector, we generated a hypomorphic allele (Cbx3hypo), which resulted in much reduced (barely detectable) levels of HP1gamma protein. Homozygotes for the hypomorphic allele (Cbx3hypo/hypo) are rare, with only 1% of Cbx3hypo/hypo animals reaching adulthood. Adult males exhibit a severe hypogonadism that is associated with a loss of germ cells, with some seminiferous tubules retaining only the supporting Sertoli cells (Sertoli cell-only phenotype). The percentage of seminiferous tubules that are positive for L1 ORF1 protein (ORF1p) in Cbx3hypo/hypo testes is greater than that for wild-type testes, indicating that L1 retrotransposon silencing is reversed, leading to ectopic expression of ORF1p in Cbx3hypo/hypo germ cells.
The Cbx3 gene product (the HP1gamma protein) has a non-redundant function during spermatogenesis that cannot be compensated for by the other two HP1 isotypes. The Cbx3hypo/hypo spermatogenesis defect is similar to that found in Miwi2 and Dnmt3L mutants. The Cbx3 gene-targeted mice generated in this study provide an appropriate model for the study of HP1gamma in transposon silencing and parental imprinting.
[Show abstract][Hide abstract] ABSTRACT: The wood lemming is unique in the following respects: (1) the sex ratio is unequal, the frequency of males is 0.20–0.30; (2) two types of females occur, type MF producing progeny of both sexes, type F producing daughters only; and (3) two sex chromosome types of females exist, XX and XY. The hypothesis presented accounts for these and other known facts concerning sex ratio, reproduction biology and chromosome constitution. It is suggested that an X-linked mutant gene affects the male-determining action of the Y, thus converting some XY animals into females. These females normally produce one kind of eggs only; by a mechanism of selective non-disjunction in the foetal ovary only X-carrying eggs are formed. Thus, XY females are of type F, XX of type MF.
[Show abstract][Hide abstract] ABSTRACT: The enzymatic activities of thiamine pyrophosphatase (TPPase), acid phosphatases (ACPases), alkaline phosphatases (APases) and steroid-3 beta-ol dehydrogenase (beta-HSDH) in different germ cells and somatic cells in the testis of three cytogenetically determined states of fertility (i.e. normal, impaired fertility and sterility) were studied histochemically in the mouse. The TPPase, ACPases and APases activities showed a characteristic stage dependent pattern when the activities were related to the typical twelve stages of the seminiferous epithelium in the mouse, according to Oakberg (1956). Comparing the enzymatic patterns of the activities in the normal spermatogenic process versus the impaired and sterile conditions, the following conclusions can be drawn: even in impaired and sterile conditions the enzymatic activity patterns retain their characteristic stage dependence; the pattern of beta-HSDH and ACPases is not altered in the impaired and sterile conditions; TPPase and APases patterns are modified in impaired and sterile mice. It is concluded that the kinetics of the enzyme activities can serve as a useful marker for characterizing pathological spermatogenic processes.
[Show abstract][Hide abstract] ABSTRACT: We have previously described the paralogous mouse genes Caspr5-1, -2, and -3 of the neurexin gene family. Here we present the cytogenetic and molecular mapping of a null mutation of Caspr5-2 which was caused by reciprocal translocation between chromosomes 1 and 8 with breakpoints at bands 1E2.1 and 8B2.1, respectively. The translocation disrupts Caspr5-2 between exons 1 and 2 and causes stillbirth or early postnatal lethality of homozygous carriers. Because no other candidate genes were found, the disruption of Caspr5-2 is most likely the cause of lethality. Only rarely do homozygotes survive the critical stage, reach fertility, and are then apparently normal. They may be rescued by one of the two other Caspr5 paralogs. Caspr5-2 is expressed in spinal cord and brain tissues. Despite giving special attention to regions where in wild-type fetuses maximum expression was found, no malformation that might have caused death could be detected in fetal homozygous carriers of the translocation. We, therefore, suspect that Caspr5-2 disruption leads to dysfunction at the cellular level rather than at the level of organ development.
[Show abstract][Hide abstract] ABSTRACT: Proteins of the Caspr family are involved in cell contacts and communication in the nervous system. We identified and, by in silico reconstruction, compiled three orthologues of the human CASPR5 gene from the mouse genome, four from the rat genome, and one each from the chimpanzee, dog, opossum, and chicken genomes. Obviously, Caspr5 gene duplications have taken place during evolution of the rodent lineage. In the rat, the four paralogues are located in one chromosome arm, Chr 13p. In the mouse, however, the three Caspr5 genes are located in two chromosomes, Chr 1 and Chr 17. RT-PCR shows that all three mouse paralogues are being expressed. Common expression is found in brain tissue but different expression patterns are seen in other organs during fetal development and in the adult stage. Tissue specificity of expression has diverged during evolution of this young rodent gene family.
[Show abstract][Hide abstract] ABSTRACT: In somatic tissues, the mouse Ki-67 protein (pKi-67) is expressed in proliferating cells only. Depending on the stage of the cell cycle, pKi-67 is associated with different nuclear domains: with euchromatin as part of the perichromosomal layer, with centromeric heterochromatin, and with the nucleolus. In gametes, sex-specific expression is evident. Mature MII oocytes contain pKi-67, whereas pKi-67 is not detectable in mature sperm. We investigated the re-establishment of the cell cycle-dependent distribution of pKi-67 during early mouse development. After fertilization, male and female pronuclei exhibited very little or no pKi-67, while polar bodies were pKi-67 positive. Towards the end of the first cell cycle, prophase chromosomes of male and female pronuclei simultaneously got decorated with pKi-67. In 2-cell embryos, the distribution pattern changed, presumably depending on the progress of development of the embryo, from a distribution all over the nucleus to a preferential location in the nucleolus precursor bodies (NPBs). From the 4-cell stage onwards, pKi-67 showed the regular nuclear relocations known from somatic tissues: during mitosis the protein was found covering the chromosome arms as a constituent of the perichromosomal layer, in early G1 it was distributed in the whole nucleus, and for the rest of the cell cycle it was associated with NPBs or with the nucleolus.
Cytogenetic and Genome Research 02/2004; 105(2-4):251-6. · 1.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We used immunolocalization in tissue sections and cytogenetic preparations of female and male gonads to study the distribution of the proliferation marker pKi-67 during meiotic cell cycles of the house mouse, Mus musculus. During male meiosis, pKi-67 was continuously present in nuclei of all stages from the spermatogonium through spermatocytes I and II up to the earliest spermatid stage (early round spermatids) when it appeared to fade out. It was not detected in later spermatid stages or sperm. During female meiosis, pKi-67 was present in prophase I oocytes of fetal ovaries. It was absent in oocytes from newborn mice and most oocytes of primordial follicles from adults. The Ki-67 protein reappeared in oocytes of growing follicles and was continuously present up to metaphase II. Thus, pKi-67 was present in all stages of cell growth and cell division while it was absent from resting oocytes and during the main stages of spermiocytogenesis. Progression through the meiotic cell cycle was associated with extensive intranuclear relocation of pKi-67. In the zygotene and pachytene stages, most of the pKi-67 colocalized with centromeric (centric and pericentric) heterochromatin and adjacent nucleoli; the heterochromatic XY body in male pachytene, however, was free of pKi-67. At early diplotene, pKi-67 was mainly associated with nucleoli. At late diplotene, diakinesis, metaphase I and metaphase II of meiosis, pKi-67 preferentially bound to the perichromosomal layer and was almost absent from the heterochromatic centromeric regions of the chromosomes. After the second division of male meiosis, the protein reappeared at the centromeric heterochromatin and an adjacent region in the earliest spermatid stage and then faded out. The general patterns of pKi-67 distribution were comparable to those in mitotic cell cycles. With respect to the timing, it is interesting to note that relocation from the nucleolus to the perichromosomal layer takes place at the G2/M-phase transition in the mitotic cell cycle but at late diplotene of prophase I in meiosis, suggesting physiological similarity of these stages.
[Show abstract][Hide abstract] ABSTRACT: The proliferation-associated nuclear protein pKi-67 relocates from the nucleolus to the chromosome surface during the G2/M transition of the cell cycle and contributes to the formation of the 'perichromosomal layer'. We investigated the in-vivo binding preferences of pKi-67 for various chromatin blocks of the mitotic chromosomes from the human and two mouse species, Mus musculus and M. caroli. All chromosomes were decorated with pKi-67 but displayed a gap of pKi-67 decoration in the centromere and NOR regions. pKi-67 distribution in a rearranged mouse chromosome showed that the formation of the centromeric gap was controlled by the specific chromatin in that region. While most chromatin served as a substrate for direct or indirect binding of pKi-67, we identified three types of chromatin that bound less or no pKi-67. These were: (1) the centromeric heterochromatin defined by the alpha satellite DNA in the human, by the mouse minor satellite in M. musculus and the 60- and 79-bp satellites in M. caroli; (2) the pericentromeric heterochromatin in M. musculus defined by the mouse major satellite, and (3) NORs in the human and in M. musculus defined by rDNA repeats. In contrast, the conspicuous blocks of pericentromeric heterochromatin in human chromosomes 1, 9 and 16 containing the 5-bp satellite showed intense pKi-67 decoration. The centromeric gap may have a biological significance for the proper attachment of the chromosomes to the mitotic spindle. In this context, our results suggest a new role for centromeric heterochromatin: the control of the centromeric gap in the perichromosomal layer.
Chromosome Research 02/2002; 10(8):685-94. · 2.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: By fluorescence in situ hybridization, we mapped the location of genes associated with the Sp100-rs cluster, a long-range repeat cluster in chromosome 1 of the house mouse, Mus musculus. The cluster comprises between 60 and 2000 repeats and extends over 6-200 Mb of the M. musculus genome, depending on the source of the cluster. The cluster evolved during the last two million years in the genus Mus in the lineage to which M. musculus belongs. The Asiatic mouse species M. caroli is not in this lineage and does not possess the cluster. M. caroli represents the ancestral genomic organization of the cluster source components Sp100, Csprs and Ifi75: they are located close to each other in the same chromosome band (1D). However, Sp100-rs, the principal gene of the cluster, is not present in the M. caroli genome. It is a chimeric M. musculus gene that arose by fusion of Csprs and the 5' part of Sp100. Sp100-rs and Ifi75 are homogeneously distributed throughout the cluster while Sp100 and Csprs in its original sequence context flank the cluster on opposite sides. Our results suggest a model for the origin and evolution of the long-range repeat cluster by duplication, gene fusion and amplification.
[Show abstract][Hide abstract] ABSTRACT: We identified and analyzed the genes Sp100, Csprs, and Ifi75 in two members of the genus Mus, M. musculus and M. caroli. Sp100 is a nuclear dot gene; Csprs and Ifi75 are novel genes encoding a putative G-protein coupled receptor (GPCR) and a putative transcriptional coactivator, respectively.
A fourth gene, Sp100-rs, occurs in M. musculus, but not in M. caroli. Sp100-rs is a chimeric gene which arose by fusion of Sp100 and Csprs copies. Sp100-rs and Ifi75 are components of a repeat cluster that extends over 6–200 Mb of the M. musculus genome. The Sp100-rs fusion gene arose only 1–2 million years ago and has become fixed and amplified in M. musculus. Although the gene is transcribed, it appears to have no function. The repeat cluster may have become fixed in the species
as a `hitchhiker' in a `selective sweep'.
[Show abstract][Hide abstract] ABSTRACT: We describe SC complements and results from comparative genomic hybridization (CGH) on mitotic and meiotic chromosomes of the zebrafish Danio rerio, the platyfish Xiphophorus maculatus and the guppy Poecilia reticulata. The three fish species represent basic steps of sex chromosome differentiation: (1) the zebrafish with an all-autosome karyotype; (2) the platyfish with genetically defined sex chromosomes but no differentiation between X and Y visible in the SC or with CGH in meiotic and mitotic chromosomes; (3) the guppy with genetically and cytogenetically differentiated sex chromosomes. The acrocentric Y chromosomes of the guppy consists of a proximal homologous and a distal differential segment. The proximal segment pairs in early pachytene with the respective X chromosome segment. The differential segment is unpaired in early pachytene but synapses later in an 'adjustment' or 'equalization' process. The segment includes a postulated sex determining region and a conspicuous variable heterochromatic region whose structure depends on the particular Y chromosome line. CGH differentiates a large block of predominantly male-specific repetitive DNA and a block of common repetitive DNA in that region.
Chromosome Research 02/2001; 9(8):659-72. · 2.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We have studied the process of tspy gene silencing in murine evolution. We have isolated functional tspy sequences from Apodemus agrarius, A. sylvaticus, A. flavicollis, and Mus platythrix (subgenus Pyromys) and nonfunctional tspy sequences from species of the subgenus Mus. We present two alternative models as to how tspy may have lost its function in the murine lineage.
[Show abstract][Hide abstract] ABSTRACT: Robertsonian (Rb) translocation heterozygosity may cause pairing problems during prophase and segregation irregularities at anaphase of meiosis I. These stages of meiosis I were studied in male mice doubly heterozygous for the two Rb chromosomes Rb(9.19)163H and Rb(16.17)8Lub. At pachytene both Rb chromosomes similarly showed pairing irregularities like unpaired segments. However, highly different nondisjunction frequencies of chromosomes forming the respective trivalents were found. The nondisjunction frequency of the Rb8Lub trivalent chromosomes was about 40%, whereas a very low frequency of nondisjunction was found in combination with the Rb163H trivalent. Since both trivalents were together in the same cell, differences in kinetochore function are assumed to be responsible for the diverse frequency of nondisjunction.
Cytogenetics and cell genetics 02/2000; 91(1-4):303-6.
[Show abstract][Hide abstract] ABSTRACT: O'Neill et al. propose that epigenetic pro-cesses help to drive karyotypic evolution in marsupials. Here we present evidence that global methylation patterns do not undergo dramatic changes in interspecific hybrids among three orders of placental mammals, indicating that the mechanisms underlying genome evolution may be different in placental mammals and marsupials.
[Show abstract][Hide abstract] ABSTRACT: Satellite DNAs (stDNAs) of four Acomys species (spiny-mice), A. cahirinus, A. cineraceus, A. dimidiatus and A. russatus, belong to closely related sequence families. Monomer sizes range from 338 to 364 bp. Between-species sequence identity was from 81.0% to 97.2%. The molecular phylogeny of the sequences helps to clarify the taxonomy of this 'difficult' group. The A. dimidiatus genome contains about 60000 repeats. According to the restriction patterns, repeats are arranged in tandem. The stDNA maps to the centromeric heterochromatin of most autosomes, both acrocentric and metacentric, but appears to be absent in the centromeric region of Y chromosomes. A well-conserved centromere protein B (CENP-B) box is present in the stDNA of A. russatus while it is degenerated in the other species.
Chromosome Research 02/1999; 7(2):131-41. · 2.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The polymorphic Sp100-rs repeat cluster in chromosome band 1D of the house mouse, Mus musculus, makes up as much as 0.1-5% of the haploid genome. 'High-copy' versions of this long-range repeat cluster are cytogenetically apparent as DAPI-negative chromomycin-A3-positive homogeneously staining regions (HSRs). The cluster is a relatively recent acquisition in the genus Mus; the related species M. caroli possesses neither the Sp100-rs cluster nor even the Sp100-rs gene. Except for chromosomes with high-copy clusters, no major rearrangements are visible in chromosomes 1 from M. musculus and M. caroli: they have the same order of G-bands, DAPI-bands and chromomycin A3-bands. Comparative genomic hybridization (CGH) visualizes the cluster in M. musculus and detects a single region of sequence homology to the cluster in M. caroli chromosome band 1D. This indicates that the M. musculus cluster has evolved in situ from sequences originally present in the same chromosome band.
Chromosome Research 02/1999; 7(8):649-53. · 2.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Three male mice with trisomy 19 induced by a Robertsonian translocation system were used for the study of meiotic prophase cells and germ cell differentiation. Present in these males were two Robertsonian chromosomes each with a chromosome 19 arm in common, two acrocentric chromosomes corresponding to the second arms of the two Rbs and one acrocentric chromosome 19. These five chromosomes showed a wide range of meiotic pairing configurations. One particular observation was the formation of a true double synaptonemal complex (SC) with three lateral axes and two central elements, which joined the three chromosomes 19 together. Integration of the acrocentric chromosome 19 in a complex pentavalent configuration was seen in 45% of the pachytene nuclei. The proportion of spermatocytes showing association between a quadrivalent and the acrocentric no. 19 was 26%. In 29% of the nuclei, the acrocentric no. 19 was free, integrated or associated with the XY complex, paired with the X chromosome or associated with a bivalent. Finally, in 57% of pachytene cells, the meiotic multivalents or the free univalent 19 were associated with the proximal part of the X chromosome or integrated in the sex chromatin. Therefore, the question arises with regard to the fate of these spermatocytes. The testicular histology shows an arrest of germ cell development at the spermatocyte stage. Several mechanisms seem to be the cause of germ cell depletion in a sequence of different, impaired developmental processes.
Chromosome Research 07/1998; 6(4):285-94. · 2.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The house mouse, Mus musculus, harbours a variable cluster of long-range repeats in chromosome 1. As shown in previous studies, some high-copy clusters such as the MUT cluster are cytogenetically apparent as a homogeneously staining region (HSR) and are associated with a distortion of the Mendelian recovery ratio when transmitted by heterozygous females. The effect is caused by a decreased viability of +/+ embryos. It is compensated by maternal or paternal MUT. In this study, a deletion derivative of MUT, MUTdel, shows normal transmission ratios and no compensating capability. In this respect, MUTdel behaves like a wild-type cluster. Hence, both properties--transmission ratio distortion and compensating capability--map to the deleted region. The deletion comprises three-quarters of the MUT HSR and does not extend to the nearest markers adjacent to the HSR.
Genetics Research 05/1998; 71(2):119-25. · 2.00 Impact Factor