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25. Neher, E. Vesicle pools and Ca
2þ
microdomains: new tools for understanding their roles in
neurotransmitter release. Neuron 20, 389–399 (1998).
26. Meyer, A. C., Neher, E. & Schneggenburger, R. Estimation of quantal size and number of functional
active zones at the calyx of held synapse by nonstationary EPSC variance analysis. J. Neurosci. 21,
7889–7900 (2001).
27. Von Gersdorff, H. & Borst, J. G. G. Short-term plasticity at the calyx of Held. Nature Rev. Neurosci. 3,
53–64 (2002).
28. Wu, L. G. & Borst, J. G. G. The reduced release probability of releasable vesicles during recovery from
short-term synaptic depression. Neuron 23, 821–832 (1999).
29. Chow, R. H., Klingauf, J., Heinemann, C., Zucker, R. S. & Neher, E. Mechanisms determining the time
course of secretion in neuroendocrine cells. Neuron 16, 369–376 (1996).
30. Helmchen, F., Borst, J. G. G. & Sakmann, B. Calcium dynamics associated with a single action
potential in a CNS presynaptic terminal. Biophys. J. 72, 1458–1471 (1997).
Acknowledgements
We thank S. Mennerick, J. H. Steinbach and R. Wilkinson for comments on the
manuscript. This work was supported by the National Science Foundation and the
National Institutes of Health.
Competing interests statement
The authors declare that they have no competing financial interests.
Correspondence and requests for materials should be addressed to L.G.W.
(e-mail: wul@morpheus.wustl.edu).
..............................................................
DMY is a Y-specific DM-domain
gene required for male development
in the medaka fish
Masaru Matsuda*, Yoshitaka Nagahama*, Ai Shinomiya†, Tadashi Sato†,
Chika Matsuda*, Tohru Kobayashi*, Craig E. Morrey*, Naoki Shibata‡,
Shuichi Asakawa§, Nobuyoshi Shimizu§, Hiroshi Horik,
Satoshi Hamaguchi† & Mitsuru Sakaizumi†
* Laboratory of Reproductive Biology, National Institute for Basic Biology,
Okazaki 444-8585, Japan
† Graduate School of Science and Technology, Niigata University, Ikarashi,
Niigata 950-2181, Japan
‡ Department of Biology, Faculty of Science, Shinshu University, Asahi 3-1-1,
Matsumoto, Nagano 390-8621, Japan
§ Department of Molecular Biology, Keio University School of Medicine,
35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
k Graduate School of Science, Nagoya University, Chikusa-ku, Nagoya 464-8602,
Japan
.............................................................................................................................................................................
Although the sex-determining gene Sry has been identified in
mammals
1
, no comparable genes have been found in non-mam-
malian vertebrates. Here, we used recombinant breakpoint anal-
ysis to restrict the sex-determining region in medaka fish
(Oryzias latipes) to a 530-kilobase (kb) stretch of the Y chromo-
some. Deletion analysis of the Y chromosome of a congenic XY
female further shortened the region to 250 kb. Shotgun sequen-
cing of this region predicted 27 genes. Three of these genes were
expressed during sexual differentiation. However, only the DM-
related
2
PG17 was Y specific; we thus named it DMY.Two
naturally occurring mutations establish DMY’s critical role in
male development. The first heritable mutant
—
a single insertion
in exon 3 and the subsequent truncation of DMY
—
resulted in all
XY female offspring. Similarly, the second XY mutant female
showed reduced DMY expression with a high proportion of XY
female offspring. During normal development, DMY is expressed
only in somatic cells of XY gonads. These findings strongly
suggest that the sex-specific DMY is required for testicular
development and is a prime candidate for the medaka sex-
determining gene.
The medaka has two major advantages for genetic research: a
large genetic diversity within the species
3,4
and the existence of
several inbred strains
5
. As in mammals, sex determination in
medaka is male heterogametic
6
, although the Y chromosome is
not cytogenetically distinct
7
. Alteration of phenotypic sex with no
reproductive consequences, and recombination over the entire sex
chromosome pair
8–10
, suggest that there are no major differences,
other than a sex-determining gene, between the X and Y chromo-
somes. To clone positionally the sex-determining region, we gener-
ated a Y congenic strain to highlight the genetic differences between
the X and Y chromosomes from inbred strains of medaka
11
. The Y
congenic strain has a sex-determining region derived from the HNI-
strain Y chromosome on the genetic background of an Hd-rR
strain. In this congenic strain, the wild-type allele (R) of the r locus
(a sex-linked pigment gene) is located only on the Y chromosome.
Therefore, the female X
r
X
r
results in a white body colour, and the
male X
r
Y
R
results in an orange-red body colour. Using this strain, we
had previously constructed a genetic map of the medaka sex
chromosome
9
.
In this study, we first performed chromosome walking using
several recombinants to map the sex-determining region of the Y
congenic strain (Fig. 1a). Two recombinants (Hd-rR.Y
HNI
(R1) and
(R2)) between the sex-determining (SD) locus and a sex-linked
marker (SL1) (centromere side of SD) were obtained from an
oestrogen-induced XY female of the Y congenic strain
9
. To obtain
recombinants between SD and r (a body-colour gene), we re-
screened progeny from an oestrogen-induced XY female of the
recombinant Hd-rR.Y
HNI
(R1) strain. We subsequently found one
white male (Hd-rR.Y
HNI
rr) and one orange-red female, which were
recombinants between the SD and r loci. After confirming their
genotypes from fin clippings, these recombinants were maintained
as strains.
For chromosome walking from SL1, we constructed a bacterial
artificial chromosome (BAC) genomic library from the Y congenic
strain. By this approach, we obtained 47 sex-linked BAC clones,
sequenced their end fragments, and designed polymerase chain
reaction (PCR) primers for sequence tag site (STS) markers on the Y
chromosome. Analyses of recombinant genotypes with these STS
markers indicated that the sex-determining region was located
between 135D12.F and 51H7.F (Fig. 1a). This stretch of the Y
chromosome was encompassed by four BAC clones (Fig. 1b),
although 19 other BAC clones included some portion of this region.
We then determined the location of the sex-determining region
on the Y chromosome by fluorescence in situ hybridization (FISH)
using one of the BAC clones as a probe. The sex-determining region
is located on the centromere side of the long arms of the sex
chromosomes (Fig. 1c, d). Centromere and DNA marker locations
on the sex chromosomes, determined using triploid hybrid
12
and
gynogenetic diploids
10
, confirmed the findings of the FISH analysis.
We used shotgun sequencing to determine the sequence covered
by the four BAC clones. The entire sequence of the two centromere-
side BAC clones (mCON089P3 and mCON144M14) was deter-
mined; however, the remaining two, telomere-side, BAC clones
(mCON104P2 and mCON137M1) could not be completely
sequenced mainly owing to numerous repetitive sequences. Con-
sequently, we sequenced 422,202 nucleotides and estimated that
the four BAC clones covered about 530 kb (Fig. 1b). The gene-
predicting program Genscan (Version 1.0, http://genes.mit.edu/
GENSCAN.html) predicted 52 genes in this region.
We also found an orange-red female in our congenic progeny
(Fig. 2). Mating this female with a sex-reversed (androgen-induced)
XX Hd-rR male resulted in all female offspring with a 50:50
(white:orange-red) body colour ratio. Assuming this female’s X
chromosome was derived from a recombination event between the
SD and r loci, sex-linked DNA markers flanking the SD locus should
be homozygous (Hd-rR/Hd-rR type). The markers (for example,
SL1 and 51H7.F) flanking the SD were heterozygous (Hd-rR/HNI
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Figure 2 Characteristics of medaka lacking a part of the Y chromosome. a, Phenotypes of
the congenic strain (XX, XY) and medaka lacking a part of the Y chromosome (XY
2
). XX
(top), XY
2
and XY (bottom) with their secondary sex characters. Males (XY) have larger
anal and dorsal fins than females (XX, XY
2
). XX have white bodies (X
r
X
r
), whereas the
others are orange-red (X
r
Y
R
). b, DNA types (SL1PG17 and 51H7.F ) of sex chromosomes.
PCR products of SL1 and PG17 were electrophoresed in a 1% agarose gel with a 1-kb
DNA ladder. AluI-digested PCR products of 51H7.F were electrophoresed in a 3% agarose
gel with a 100-bp DNA ladder. SL1 and 51H7.F are homozygous in XX and YY (Hd-rR or
HNI type), but are heterozygous in XY
2
and XY (Hd-rR/HNI type). PG17 is present in XY and
YY but absent in XX and XY
2
. These results indicate that PG17 is specific to the Y
chromosome but absent from the Y chromosome of XY
2
. Specific primers for PG17 and
51H7.F were as follows: PG17: PG17.19, GAACCACAGCTTGAAGACCCCGCTGA;
PG17.20, GCATCTGCTGGTACTGCTGGTAGTTG; and 51H7.F : 51H7.F2,
CAGGCCTTGAAGATCAACGAGT; 51H7.F3, AGTGCATCTAGTGTACATGGGT.
c, Histological cross-sections of medaka fry sampled 30 d.a.h.. Sex chromosome types
were determined by PCR using DNA extracted from the head. Black arrowheads indicate
gonads. XX and XY
2
individuals have ovaries with several oocytes, whereas XY specimens
have testes with spermatogonia. Scale bars, 50
m
m.
Figure 1 Positional cloning strategy of the sex-determining region and subsequent
identification of PG17/DMY. a, Genetic maps of the sex-determining regions and Y
chromosomes of the recombinant strains. Pink indicates regions derived from an HNI Y
chromosome; yellow represents Hd-rR X-chromosome-derived regions. b, BAC contigs
and a physical map of the sex-determining region. Horizontal bars indicate BAC clones.
Blue blocks show the sequenced regions. c, d, Cytogenetical mapping of the sex-
determining region of medaka. c, FISH of metaphase chromosomes. SL2 (red) localizes on
the short arms of the sex chromosomes, whereas a BAC clone containing SL1
(mCON072N5, yellow) localizes on the long arms. Arrowheads indicate sex
chromosomes. d, FISH of one sex chromosome with three different probes (SL2, SL1, SD).
Signals of a BAC clone containing the sex-determining region (mCON049E13) are light
blue. The arrowhead shows the centromere region. e, The Y chromosome of medaka
lacking a part of the sex-determining region. DNA markers were not detected between
PG31C and A314482, but were detected on the centromere side of PG04 and the
telomere side of PG31T. Respective location of PG17, PG21 and PG30 within the sex-
determining region between PG04 and PG31T is shown. f, RT–PCR analysis for PG17,
PG21 and PG30 mRNA expression in whole Hd-rR.Y
HNI
embryos at hatching. Sex
chromosome types were determined by SL1 PCR. PG17 expression was detected by
nested PCR (see Methods). g, h, Structure and sequences of PG17/DMY. g, Structural
analysis of the PG17/DMY showing exons (open boxes), the DM domain (grey boxes) and
introns (horizontal lines) of PG17. Translation start and stop sites are indicated by ATG and
STOP, respectively. Numbers represent nucleotide sequence length (base pairs, bp).
h, Amino-acid sequence of wild-type PG17/DMT and the PG17
wAwr
mutation. The DM
domain is boxed. A frame shift (italicized) occurs in the region from amino acid 110 to
premature termination (amino acid 139).
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type), indicating that this particular orange-red female had the
congenic sex-determining region on the Y chromosome (Fig. 2b), a
conclusion confirmed by other DNA markers within the sex-
determining region. From these observations, this XY female was
determined to lack 250 kb within the sex-determining region of the
Y chromosome (Fig. 1e). Consequently, the corresponding region of
a normal Y chromosome should contain the sex-determining gene.
Genscan analysis of the deleted 250-kb region predicted 27 genes.
To identify which predicted genes were expressed, we designed
specific primers for each, and examined their expression in medaka
embryos during sexual differentiation (before hatching to 10 days
after hatching, d.a.h.). PCR with reverse transcription (RT–PCR)
detected expression of three of these 27 genes in embryos (Fig. 1f).
Furthermore, only one of these three genes, PG17 (predicted gene
17)/DMY, was expressed exclusively in XYembryos. In contrast, the
remaining two genes (PG21, PG30) were expressed in both XY and
XX embryos. BAC clones derived from the X and Y chromosomes
confirmed that PG17 is specific to the Y chromosome whereas the
other two genes are present on both the X and Y chromosomes.
The full-length complementary DNA sequence (1,320 base pairs)
of DMY was obtained by 5
0
and 3
0
rapid amplification of cloned
ends (RACE). The longest open reading frame spans six exons and
encodes a putative protein of 267 amino acids, including the highly
conserved DM domain (Fig. 1g, h). The DM domain was originally
described as a DNA-binding motif shared between doublesex (dsx)
in Drosophila melanogaster and mab-3 in Caenorhabditis elegans
2
.
Since the initial characterizations of dsx and mab-3, DM-related
genes have been identified from virtually all species examined,
including medaka
13–19
. In vertebrate species, DMRT1 (DM-related
transcription factor 1), the DM-related gene most homologous to
DMY (about 80%; data not shown), correlates with male develop-
ment
13–18,20
. Combined with its Y chromosome specificity, this
finding suggests that DMY is pivotal in testicular differentiation.
To establish a role for DMY during sexual differentiation, we
screened wild medaka populations for naturally occurring DMY
mutants. Two XY females with distinct mutations in DMY were
found in separate populations (Awara and Shirone). The XY
wAwr
mutant from Awara contains a single nucleotide insertion in exon 3
of DMY. Although the DM domain remains intact, this insertion
causes a frame shift from residue 110 and premature termination at
residue 139 (Fig. 1h). Offspring obtained by mating the XY
wAwr
female with an Hd-rR male (XY, DMY on Y chromosome) revealed
typical mendelian combinations (XX, XY, XY
wAwr
,YY
wAwr
); how-
ever, phenotypes were female, male, female and male, respectively
(Table 1). Despite the presence of pseudo-DMY messenger RNA
(which does not encode full-length DMY) in offspring containing
the PG17
wAwr
mutant allele (Fig. 1h), the absence of about two-
thirds of the protein presumably renders DMY nonfunctional, thus
resulting in XY sex reversal (female phenotype). Although the
mechanism apparently differs, the second mutant also results in
XY sex reversal. The entire DMY coding region of the XY
wSrn
mutant
is intact; however, an unknown transcriptional anomaly severely
depresses or eliminates DMY expression in embryos (Fig. 3). In
addition to the original XY
wSrn
female mutant, 60% of XY
wSrn
offspring developed as phenotypic females (Table 1), suggesting that
a threshold level of DMY expression is required for male develop-
ment. Taken together, the loss-of-function mutant (XY
wAwr
) and the
depressed expression mutant (XY
wSrn
) strongly suggest that DMY is
Table 1 Genotype and gonadal phenotype ratios
Cross Genotype
Gonadal phenotype
ratio (ovary:testis)
Fry Adults
.............................................................................................................................................................................
XY
wAwr
(female) £ Hd-rR (male) XX 7: 0 11: 0
XY
wAwr
10: 0 8: 0
XY
Hd-rR
0: 11 0: 5
YY 0: 8 0: 2
XY
wSrn
(female) £ Hd-rR (male) XX NA 15: 0
XY
wSrn
NA 9: 6
XY
Hd-rR
NA 0: 9
YY NA 0: 8
.............................................................................................................................................................................
Ratios are from progeny of mutant female £ Hd-rR male crosses. Sex chromosome type was
determined from SL1 and PG17 genotypes. NA, not applicable (fry were not analysed).
Figure 3 cDNA PCR of progeny from XY
wAwr
and XY
wSrn
female £ Hd-rR male crosses. A
PG17/DMY band was detected in XY
Hd-rR
and XY
wAwr
embryos but not in XY
wSrn
embryos.
Total RNA (150 ng each) was extracted from whole embryos (at hatching) and used for
cDNA synthesis and amplification using the SMART PCR cDNA Synthesis Kit (Clontech)
according to the manufacturer’s protocol. Amplified cDNA and genomic DNA were used
as PCR templates of PG04 and PG17 (PG17.19–20 primer set). Specific primers for PG04
were as follows: PG04.1, CCAGCGGTTTGAGGATAGGTTTG; PG04.2,
GAGCTTTCTGCAGGGCGACTTTC. Products were electrophoresed in a 2% agarose gel
with a 100-bp DNA ladder.
Figure 4 PG17/DMY mRNA expression in fry gonads shown by digoxigenin-labelled in situ
hybridization of larval sections. a, XY gonads on hatching day; antisense probe. Strong
signals for PG17/DMY were seen in cells surrounding the germ cells. G, germ cell; CE,
coelomic epithelium; ND, nephric duct. b, XX gonad on hatching day; antisense probe.
PG17/DMY signal was undetectable in XX individuals. c, XY gonad on hatching day; sense
probe. Control hybridization showed no signal. Scale bar, 20
m
m.
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required for normal testicular differentiation.
To confirm the role of DMY during normal development, in situ
hybridization was used to determine its spatial expression during
gonadal differentiation. Because DMRT1 and DMY are very similar,
the in situ hybridization probe was not able to discriminate between
the two mRNAs. We therefore determined the temporal expression of
both DMY and DMRT1 during sexual differentiation using specific
RT–PCR. At hatching and 5 d.a.h., DMY mRNA was present in XY
embryos, but not in XX embryos. In contrast, there was no DMRT1
expression in either XX or XYembryos at either of these time points
(data not shown). Because expression of DMY and DMRT1 do not
appear to overlap during this period, we assumed that the in situ
hybridization signal represented DMY expression. As predicted from
our PCR studies, DMY signal was detected only in the somatic cells
surrounding germ cells in XYembryos (Fig. 4). Although its function
in the pre-Sertoli cells remains unclear, these data further indicate
that DMY has a critical role in testicular differentiation.
Although evidence of sufficiency is required to definitively
identify DMY as a sex-determining gene, we have shown that it is
necessary for normal male development and falls within the sex-
determining region of the Y chromosome. Given the absence of
other reasonable candidate genes within the region, DMY is cer-
tainly the leading candidate for the medaka sex-determining gene.
Interestingly, phylogenetic analyses indicate that DMY was probably
derived from DMRT1, suggesting an evolutionary pattern similar to
one of the proposed origins of Sry. Sry is thought to have either
arisen from an autosomal Sox gene duplication event and sub-
sequent formation of the Y chromosome or, more probably,
divergence from Sox3 after formation of the sex (X) chromosomes
21
.
Regardless, the linkage of Sry to the Y chromosome renders the
entire male pathway dependent on Sry. Further evidence concerning
the ability of DMY to trigger male development and its evolutionary
relationship to DMRT1 are needed to confirm this hypothesis, but
the linkage of DMY to the Y chromosome and its requirement for
testicular differentiation strongly suggest that DMY represents a
non-mammalian vertebrate equivalent of Sry. A
Methods
Fish
Two recombinant strains between SL1 and SD, Hd-rR.Y
HNI
(R1) and Hd-rR.Y
HNI
(R2),
were established from recombinant offspring of sex-reversed XY females of the described
Hd-rR.Y
HNI
strain
9
. Another recombinant strain, Hd-rR.Y
HNI
rr, was established from a
recombinant between SD and r. This recombinant was obtained from offspring of a sex-
reversed Hd-rR.Y
HNI
(R1) XY female crossed with a sex-reversed Hd-rR XX male. Sex
reversal in medaka was accomplished by oestrogen (XY females) or androgen (XX males)
treatment during early development, according to previously published methods
9
.
Naturally occurring mutants XY
wAwr
and XY
wSrn
were found in wild populations near
Awara (Fukui prefecture) and Shirone (Niigata prefecture), Japan, respectively.
RNA and DNA extraction
Total RNA and genomic DNA were extracted from each hatched embryo after
homogenization in a 1.5-ml tube with 350
m
l RLT buffer supplied with the RNeasy Mini
Kit (Qiagen). The homogenized lysates were centrifuged and supernatants were used for
RNA extraction using the RNeasy Mini Kit with the RNase-Free DNase set protocol
(Qiagen). Precipitated material was used for DNA extraction using the DNeasy tissue Kit
(Qiagen) according to the manufacturer’s protocol.
Chromosome walking
A BAC genomic library was constructed from the Y congenic Hd-rR.Y
HNI
strain as
described
22
. High-molecular-mass genomic DNA was extracted from sperm, partially
digested with HindIII, and selected for a size range of 150–250 kb. The size-selected DNA
fragments were ligated to pBAC-lac
23
and used to transform DH10B. A total of 55,292 BAC
clones was picked and arrayed to 144 microtitre plates each with 384 wells. The library was
gridded at high density on Hybond-N þ nylon membranes (Amersham Pharmacia
Biotech). Chromosome walking started at SL1. Two-thirds of the library was usually
screened. Inserted end fragments of positive BAC clones were amplified by vectorette
PCR
24
and used for assembling the positive clones. An amplified end fragment at the far
end of the SD side was used in subsequent screening of the BAC library.
RT–PCR
First-strand cDNA was synthesized from 0.5
m
g total RNA in 25
m
l using PowerScript
(Clontech) with oligo-dT primers. PCR was carried out in a 25
m
l reaction mixture
containing 0.25
m
l of the first-strand cDNA. PCR conditions were 5 min at 95 8C; 20 s at
96 8C, 30 s at 55 8C, 30 s at 72 8C for 30 cycles; and 5 min at 72 8C. For PG17, 0.01
m
lofthe
initial PCR products were re-amplified under the same conditions. Specific primers for
each gene were as follows; PG17
—
first PG17.11, GAGTCGGAGCCAAGCGGGTACAA
CATTC, PG17.12, GACCATCTCATTTTTTATTCTTGATTTT, second PG17.5,
CCGGGTGCCCAAGTGCTCCCGCTG, PG17.6, GATCGTCCCTCCACAGAGAAGAGA;
PG21
—
PG21.1, TGTGATTCTGAAGGGGGAGTTTGTAA, PG21.3, GACCTCCAGAGTC
ATCTTGCACAC); and PG30
—
PG30.1, GGAGGAAAGTGTCAGGAGTGTTGTGT,
PG30.2, GCCGTCCCTCTGATGTACTCGTTCCT).
FISH mapping
Metaphase cells from Hd-rR embryos were prepared by standard cytogenetic methods
25
.
FISH was performed using an SL2 fragment labelled by PCR
9
with digoxigenin-11-dUTP
(Boehringer) and BAC clones mCON072N5 (containing SL1) and mCON049E13 (SD
region) labelled by nick translation with fluorescein and biotin, respectively. Cells were co-
hybridized with SL2 and SL1 or SL2, SL1 and SD, and counterstained with 4,6-diamidino-
2-phenylindole (DAPI). Probes were detected with rhodamine-labelled anti-digoxigenin
antibodies (Boehringer), Alexa Fluor 488-labelled anti-fluorescein, and Alexa Fluor 660-
labelled streptavidin (Molecular Probes). Metaphase cells were examined using four filters
(A4, L5, N3 and Y5) and images were captured using a CoolSNAP charge-coupled device
camera (Nippon roper) and Openlab software (Improvision). Hybridization was detected
on the identical sex chromosome.
Shotgun sequencing
BAC DNA was hydrodynamically sheared to average sizes of 1.5 and 4.5 kb, and the DNA
was ligated into a pUC18 vector. We sequenced each BAC to 13 coverage using
Dyeterminatore chemistry. Individual BACs were assembled from the shotgun sequences
using phred Version 0.000925.c, crossmatch Version 0.990319 and phrap Version 0.990319
(Codon Code), and PCP Version 2.1.6 and CAP4 Version 2.1.6 (Paracel). The gaps in each
BAC were closed using a combination of BAC walking, directed PCR and re-sequencing of
individual clones.
Analyses of wild mutants
We crossed wild mutant females (XY; 2/PG17
wAwr
or XY; 2/PG17
wSrn
) with Hd-rR males
(XY; 2/PG17
Hd-rR
) to obtain the following sex chromosomes and PG17 genotypes in the
offspring: XX; 2/2,XY;2/PG17
wAwr
,XY;2/PG17
Hd-rR
, and YY; PG17
wAwr
/PG17
Hd-rR
.
Genotypes of these offspring were determined by genomic PCR of PG17 and SL1. PG17
expression was examined by RT–PCR (see above). Sexes were confirmed by histological
examination of gonads (fry and adult fish) and secondary sex characteristics (adult fish).
At hatching, germ cell numbers were counted to determine gonadal phenotype
26
.Exon
sequences of the mutant PG17 genes (PG17
wAwr
and PG17
wSrn
) were determined using
DNA extracted from the mutants and their progeny.
In situ hybridization
Gonads of 0–5 d.a.h. Hd-rR fry were dissected with trunk of the body and fixed in 4%
paraformaldehyde in 0.1 M phosphase buffer (pH 7.4) at 4 8C overnight. After fixation,
gonads were embedded in paraffin and cross-sectioned at 5
m
m. In situ hybridization was
performed using published methods
27
. Genetic sex of fry was confirmed by PCR using the
SL1 genotype
11
.
Received 22 February; accepted 24 April 2002.
Published online 12 May 2002, DOI 10.1038/nature751.
1. Sinclair, A. H. et al. A gene from the human sex-determining region encodes a protein with homology
to a conserved DNA-binding motif. Nature 346, 240–244 (1990).
2. Raymond, C. S. et al. Evidence for evolutionary conservation of sex-determining genes. Nature 391,
691–695 (1998).
3. Sakaizumi, M., Moriwaki, K. & Egami, N. Allozymic variation and regional differentiation in wild
populations of the fish Oryzias latipes. Copeia 1983, 311–318 (1983).
4. Matsuda, M., Yonekawa, H., Hamaguchi, S. & Sakaizumi, M. Geographic variation and diversity in
the mitochondrial DNA of the medaka, Oryzias latipes, as determined by restriction endonuclease
analysis. Zool. Sci. 14, 517–526 (1997).
5. Hyodo-Taguchi, Y. & Sakaizumi, M. List of inbred strains of the medaka, Oryzias latipes, maintained
in the Division of Biology, National Institute of Radiological Sciences. Fish Biol. J. MEDAKA 5, 29–30
(1993).
6. Aida, T. On the inheritance of colour in a freshwater fish, Aplocheilus latipes Temminck and Schlegel,
with special reference to sex-linked inheritance. Genetics 6, 554–573 (1921).
7. Uwa, H. & Ojima, Y. Detailed and banding karyotype analysis of the medaka, Oryzias latipes,in
cultured cells. Proc. Jpn Acad. B 57, 39–43 (1981).
8. Yamamoto, T. Progenies of sex-reversal females mated with sex-reversal males in the medaka, Oryzias
latipes. J. Exp. Zool. 146, 163–179 (1961).
9. Matsuda, M., Sotoyama, S., Hamaguchi, S. & Sakaizumi, M. Male-specific restriction of
recombination frequency in the sex chromosomes of the medaka, Oryzias latipes. Genet. Res. 73,
225–231 (1999).
10. Kondo, M., Nagao, E., Mitani, H. & Shima, A. Differences in recombination frequencies during female
and male meioses of the sex chromosomes of the medaka, Oryzias latipes. Genet. Res. 78, 23–30 (2001).
11. Matsuda, M. et al. Isolation of a sex chromosome-specific DNA sequence in the medaka, Oryzias
latipes. Genes Genet. Syst. 72, 263–268 (1997).
12. Sato, T., Yokomizo, S., Matsuda, M., Hamaguchi, S. & Sakaizumi, M. Gene-centromere mapping of
medaka sex chromosomes using triploid hybrids between Oryzias latipes and O. luzonensis. Genetica
111, 71–75 (2001).
13. Raymond, C. S., Kettlewell, J. R., Hirsch, B., Bardwell, V. J. & Zarkower, D. Expression of Dmrt1 in the
genital ridge of mouse and chicken embryos suggests a role in vertebrate sexual development. Dev.
Biol. 215, 208–220 (1999).
14. Smith, C. A., McClive, P. J., Western, P. S., Reed, K. J. & Sinclair, A. H. Conservation of a sex-
letters to nature
NATURE | VOL 417 | 30 MAY 2002 | www.nature.com562
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Nature
Publishing
Group
determining gene. Nature 402, 601–602 (1999).
15. De Grandi, A. et al. The expression pattern of a mouse doublesex-related gene is consistent with a role
in gonadal differentiation. Mech. Dev. 90, 323–326 (2000).
16. Kettlewell, J. R., Raymond, C. S. & Zarkower, D. Temperature-dependent expression of turtle Dmrt1
prior to sexual differentiation. Genesis 26, 174–178 (2000).
17. Marchand, O. et al. DMRT1 expression during gonadal differentiation and spermatogenesis in the
rainbow trout, Oncorhynchus mykiss. Biochim. Biophys. Acta 1493, 180–187 (2000).
18. Guan, G., Kobayashi, T. & Nagahama, Y. Sexually dimorphic expression of two types of DM
(Doublesex/Mab-3)-domain genes in a teleost fish, the tilapia (Oreochromis niloticus). Biochem.
Biophys. Res. Commun. 272, 662–666 (2000).
19. Brunner, B. et al. Genomic organization and expression of the doublesex-related gene cluster in
vertebrates and detection of putative regulatory regions for dmrt1. Genomics 1, 8–17 (2001).
20. Moniot, B., Berta, P., Scherer, G., Sudbeck, P. & Poulat, F. Male specific expression suggests role of
DMRT1 in human sex determination. Mech. Dev. 91, 323–325 (2000).
21. Schepers, G. & Koopman, P. Phylogeny of the SOX family of developmental transcription factors
based on sequence and structural indicators. Dev. Biol. 227, 239–255 (2000).
22. Matsuda, M. et al. Construction of a BAC library derived from the inbred Hd-rR strain of the teleost
fish, Oryzias latipes. Genes Genet. Syst. 76, 61–63 (2001).
23. Asakawa, S. et al. Human BAC library: construction and rapid screening. Gene 191, 69–79 (1997).
24. Ragoussis, J. & Olavesen, M. G. in Genome Mapping: A Practical Approach (ed. Dear, P. H.) 253–260
(Oxford Univ. Press, New York, 1997).
25. Matsuda, M., Matsuda, C., Hamaguchi, S. & Sakaizumi, M. Identification of the sex chromosomes of
the medaka, Oryzias latipes, by fluorescence in situ hybridization. Cytogenet. Cell Genet. 82, 257–262
(1998).
26. Hamaguchi, S. A light- and electron-microscopic study on the migration of primordial germ cells in
the teleost, Oryzias latipes. Cell Tissue Res. 227, 139–151 (1982).
27. Kobayashi, T., Kajiura-Kobayashi, H. & Naghama, Y. Differential expression of vasa homologue gene
in the germ cells during oogenesis and spermatogenesis in a teleost fish, tilapia, Oreochromis niloticus.
Mech. Dev. 99, 139–142 (2000).
Acknowledgements
We are grateful to P. Koopman for advice; G. Young for critical reading of the manuscript;
and M. Takeda, E. Uno and R. Hayakawa for technical assistance. This work was supported
in part by Grants-in-Aid for Research for the Future from the Japan Society for the
Promotion of Science, Scientific Research of Priority Area, Environmental Endocrine
Disrupter Studies from the Ministry of the Environment, Bio Design from the Ministry of
Agriculture, Forestry and Fisheries, and Japan Society for the Promotion of Science
Research Fellowships for Young Scientists.
Competing interests statement
The authors declare that they have no competing financial interests.
Correspondence and requests for materials should be addressed to Y.N.
(e-mail: nagahama@nibb.ac.jp). The DNA Data Bank of Japan (DDBJ) accession number of the
medaka DMY cDNA sequence is AB071534.
..............................................................
Transcription coactivator TRAP220 is
required for PPAR
g
2-stimulated
adipogenesis
Kai Ge*, Mohamed Guermah*, Chao-Xing Yuan*‡, Mitsuhiro Ito*,
Annika E. Wallberg*, Bruce M. Spiegelman† & Robert G. Roeder*
* Laboratory of Biochemistry and Molecular Biology, The Rockefeller University,
1230 York Avenue, New York, New York 10021, USA
† Dana-Farber Cancer Institute and Department of Cell Biology, Harvard
Medical School, Boston, Massachusetts 02115, USA
.............................................................................................................................................................................
The TRAP (thyroid hormone receptor-associated proteins) tran-
scription coactivator complex (also known as Mediator) was first
isolated as a group of proteins that facilitate the function of the
thyroid hormone receptor
1
. This complex interacts physically
with several nuclear receptors through the TRAP220 subunit,
and with diverse activators through other subunits
2
. TRAP220
has been reported to show ligand-enhanced interaction with
peroxisome proliferator-activated receptor
g
2(PPAR
g
2)
3,4
,a
nuclear receptor essential for adipogenesis
5–8
. Here we show
that Trap220
2/2
fibroblasts are refractory to PPAR
g
2-stimulated
adipogenesis, but not to MyoD-stimulated myogenesis, and do
not express adipogenesis markers or PPAR
g
2 target genes. These
defects can be restored by expression of exogenous TRAP220.
Further indicative of a direct role for TRAP220 in PPAR
g
2
function via the TRAP complex, TRAP functions directly as a
transcriptional coactivator for PPAR
g
2 in a purified in vitro
system and interacts with PPAR
g
2 in a ligand- and TRAP220-
dependent manner. These data indicate that TRAP220 acts, via
the TRAP complex, as a PPAR
g
2-selective coactivator and,
accordingly, that it is specific for one fibroblast differentiation
pathway (adipogenesis) relative to another (myogenesis).
PPAR
g
is a key regulator of transcriptional pathways important
for adipogenesis
8
. Retrovirus vector-mediated ectopic expression of
PPAR
g
2 alone can stimulate mouse embryonic fibroblasts (MEFs)
to undergo adipogenesis
9,10
.PPAR
g
is a member of the nuclear
hormone receptor superfamily of DNA binding transcriptional
activators that, in a ligand-dependent manner, activate specific
target genes important for cell growth, cell differentiation and
homeostasis. Like other transcriptional activators, nuclear receptors
act through a variety of interacting transcriptional coactivators that
act either to modify chromatin structure or at subsequent steps such
as preinitiation complex (PIC) assembly and function
2,11
.The
mammalian TRAP complex, like the distantly related yeast
Mediator, appears to play the main role in direct communication
between diverse activators and the general transcription factors that
form the PIC
2,12–19
. The demonstration of ligand-dependent inter-
actions of the TRAP220 subunit of the TRAP complex with multiple
nuclear receptors suggested a broad role for TRAP in nuclear
receptor function and associated physiological processes
4
. As the
TRAP220 subunit of the TRAP complex has been shown to interact
physically with PPAR
g
2
3,4
, we sought to investigate the physiologi-
cal role of TRAP220, and the possible involvement of the entire
TRAP complex, in PPAR
g
2-stimulated adipogenesis and target
Figure 1 Trap220
2/2
MEFs have defects in PPAR
g
2-stimulated adipogenesis. Cells
infected with either a control retroviral vector (pMSCVpuro) or one expressing PPAR
g
2
(pMSCV-PPAR
g
2) were induced with differentiation medium in the presence or absence
of 0.5
m
M synthetic PPAR
g
ligand rosiglitazone. At day 8 post-induction, cells were either
stained for lipid droplets with Oil Red O or total RNA was extracted and subjected to
northern blot. a, Morphological differentiation shown by Oil Red O staining. b, Northern
blot analysis of gene expression pattern. KO, Trap220
2/2
cells; WT, wild-type cells.‡ Present address: Bristol-Myers Squibb, Wilmington, Delaware 19803, USA.
letters to nature
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