Testicular type Sox9 is not involved in sex determination but might be in the development of testicular structures in the medaka, Oryzias latipes

Isolation and expression of two distinct Sox8 genes in mudloach (Misgurnus anguillicaudatus)

To investigate the function and evolutionary origin of the SOXE subgroup, we amplified the genomic DNA of Misgurnus anguillicaudatus using a pair of degenerate primers. Using RACE, we obtained two versions of Sox8 (MaSox8a and MaSox8b) from M. anguillicaudatus. The overall sequence identity of the deduced amino acids from the two genes was 54.38%, with only one amino acid change in the high-mobility group domain. Southern blotting and evidence from the phylogenetic tree provided further proof for the existence of two Sox8 genes at the genomic level. This is the first evidence of two distinct Sox8 genes in Cypriniformes. Semi-quantitative and real-time quantitative PCR assays showed the expression trend of the genes was opposite in early embryonic development, and both were expressed ubiquitously in several adult tissues. The similar expression patterns indicated that MaSox8a and MaSox8b have possible overlapping functions.

Isolation of sox9 duplicates in catfish: localization, differential expression pattern during gonadal development and recrudescence, and hCG-induced up-regulation of sox9 in testicular slices

In vertebrates, sox9 is a transcription factor that plays a crucial role in testicular development and chondrogenesis. Here, we report cloning of isoforms of sox9 (sox9a and sox9b) from air-breathing catfish Clarias gariepinus, which undergoes an annual reproductive cycle. Tissue distribution pattern showed differential expression of sox9 duplicates, wherein both forms were highly expressed in brain and gonads. Furthermore, we observed a dimorphic expression pattern of sox9a and sox9b in both adult and developing gonads using RT-PCR, indicating that sox9a retained its function in testis while sox9b might have a new role to play in ovary. Changes in sox9 mRNA levels using real-time quantitative PCR (qRT-PCR) during the seasonal reproductive cycle revealed that sox9a transcript in testis was abundant during testicular recrudescence (during spermatogenesis), and its expression significantly decreased during spawning and post-spawning phases. Furthermore, treatments of human chorionic gonadotropin and 11-ketotestosterone in vitro up-regulated sox9a mRNA levels in the testicular slices at 12 and 24 h time points, suggesting that gonadotropins might stimulate sox9 expression. These results suggest that sox9 might have a plausible role in the entrainment of the testicular cycle. In contrast, during the ovarian cycle, sox9b mRNA levels gradually declined from preparatory to post-spawning phases. Immunohistochemical (IHC) data showed that, in testis, sox9 is detectable in Sertoli and spermatogonial cell types except spermatid/spermatozoa. In the ovary, it is localized in the ooplasm of primary and pre-vitellogenic oocytes. These results were further confirmed by whole-mount IHC and qRT-PCR.

Isolation and expression analyses of the Sox9a gene in triploid crucian carp

To investigate the evolutional significance of Sox9 in fish, we isolated and characterized Sox9a cDNA and genomic clones in triploid crucian carp. The cDNA encoded a protein of 457 amino acids with an HMG box and showed more than 60% amino acid sequence identity with known vertebrate Sox9 proteins. Triploid crucian carp and vertebrate Sox9s showed similar gene structure, and two introns in the coding region were located at conserved positions. On the basis of the amino acid sequences, Sox9a can be categorized into the same subgroup of Sox-E proteins as Sox8, 9, and 10. Interestingly, the expression of triploid crucian carp Sox9a was predominantly observed not in the ovary but in the testis by Northern blot and RT-PCR analysis. The expression analysis of Sox9a suggested that it may seldom contribute to the formation of normal functions of spermatozoa, but it may play an important role in the development of testicular tubules. Besides the testicular expression, Sox9a was also shown to be expressed in many other tissues including the brain, kidney, and heart of triploid crucian carp, indicating that Sox9 may have unique functions in some specific tissues during development.

Real-time PCR-based prediction of gonad phenotype in medaka

An important endpoint in aquatic bioassays for potential endocrine disrupting chemicals (EDCs) is the gonadal phenotype of exposed fish, with special interest in intersex and sex-reversed individuals. Traditionally, the assessment of gonad phenotype is done via histology, which involves specialized and time-consuming techniques. The method detailed here increases the efficiency of the analysis by first determining the relative expression of four genes involved in gonad development/maintenance in Japanese medaka (Oryzias latipes), and then by using principal component analysis, assigning a phenotype to each gonad based upon the gene expression data. The gonad phenotype and the sexual genotype, which can be determined in medaka, can then be compared to assess potential adverse effects of exposure to endocrine disrupting chemicals.

In search of determinants: gene expression during gonadal sex differentiation

The diversity of inputs that guide sexual fate during development is both intriguing and daunting. In the field of fish biology, the study of sex determination is of great importance. For example, in aquaculture, sexually dimorphic growth rates and overall size leads to one sex being more marketable than the other. Moreover, for breeding purposes it is important to maintain balanced sex ratios. Furthermore, sex determination is sensitive to environmental factors, such as temperature and contaminants, which can lead to skewed sex ratios, intersexes and sterility in wild or farmed fish. The gonad is typically the first organ to exhibit morphological signs of sexual dimorphism and therefore is likely to be the primary organ system whose fate is controlled by the sex determination cues in many fish species. Additionally, the sexual fate of the gonad has been shown to fully or partially control organismal sex differentiation. Thus, understanding the genetic regulation of gonadal sex differentiation is critical in studies of fish sex determination. This review summarizes recent knowledge of genes expressed during gonadal sex differentiation in gonochoristic teleost fish. Three species are discussed, which serve as excellent model systems for probing teleost sex differentiation: the Oreochromis niloticus, Oryzias latipes and Danio rerio. The similarities and differences between gonadal gene expression in these three species and in comparison to mammals suggest conserved roles during vertebrate gonadal sex differentiation. In the future, it will be essential to develop tools to assay the function of genes expressed during gonadal sex differentiation in fish.

Estrogen represses SOX9 during sex determination in the red-eared slider turtle Trachemys scripta

Production of male offspring in viviparous eutherian mammals requires a sex-determining mechanism resistant to maternal hormones. This constraint is relaxed in egg-laying species, which are sensitive to hormones during sex determination and often use an increase in aromatase, the estrogen-synthesizing enzyme, as a key feminizing signal. In the turtle Trachemys scripta, sex is normally determined by temperature, but estrogen treatment overrides this cue and leads exclusively to female development. We assessed whether the expression of SOX9, a central male sex-determining gene in mammals, or three other conserved transcription factors (WT1, GATA4, and LHX9) was regulated by estrogen signaling in the turtle. As in mice, all somatic cell types in the immature turtle gonad initially expressed WT1 and GATA4, whereas SOX9 was restricted to the Sertoli precursors and LHX9 to the coelomic epithelium and interstitium. After the bipotential period, SOX9 was abruptly down-regulated at the female temperature. Strikingly, embryos treated with beta-estradiol at the male temperature lost SOX9 expression more than two stages earlier than controls, though WT1, GATA4, and LHX9 were unaffected. Conversely, inhibition of estrogen synthesis and signaling prevented or delayed SOX9 down-regulation at the female temperature. These results suggest that endogenous estrogen feminizes the medulla of the bipotential turtle gonad by inhibiting SOX9 expression. This mechanism may be involved in the male-to-female sex reversal in wild populations exposed to environmental estrogens, and is consistent with results showing that the estrogen receptor represses Sox9 to block transdifferentiation of granulosa cells into Sertoli-like cells in the adult mouse ovary.

Molecular characterization of cyp11a1 and cyp11b1 and their gene expression profile in pejerrey (Odontesthes bonariensis) during early gonadal development

Sex steroids are known to be involved in gonadal differentiation in fish, but whether androgens are early mediators of testis differentiation remains unclear. We studied the sex-related developmental variations in the gene expression of two key enzymes involved in steroids and androgen synthesis (cyp11a1 and cyp11b1) in trunks and isolated gonads of pejerrey (Odontesthes bonariensis) larvae during and after the sex determination period. Also, and in order to have a better characterization of this process we studied the expression of Sertoli (dmrt1, amh, sox9) and Leydig (nr5a1 or sf-1) cell markers as well as a gene with higher expression in females (cyp19a1a). No clear differences were observed in the expression of cyp11a1 and cyp11b1 during the temperature-sensitive window in the trunk of pejerrey larvae. Nevertheless, a clear increase of cyp11b1 was observed in isolated gonads taken from fish reared at the male producing temperature. In these gonads we also confirmed the trends of genes with higher expression in males (dmrt1, amh) and females (cyp19a1a) as previously described in larval trunks of pejerrey. Our results showed that the expression of cyp11b1 was positively associated with the morphological differentiation of the testis. Nevertheless the involvement of 11-oxygenated androgens during the temperature-sensitive window could not be clearly established.

Expression profiles of sex differentiation-related genes during ontogenesis in the European sea bass acclimated to two different temperatures

The European sea bass is a teleost fish that lacks sex chromosomes and for which temperature influences sex ratios. However, correlation between temperature, developmental stage at a given age and sex-specific gene expression is hampered by the lack of sex markers. To study this correlation, fish were exposed to feminizing (15 degrees C) or masculinizing temperature (21 degrees C) from 0-120 days post fertilization, throughout the thermosensitive period (TSP). Aromatase (cyp19a1a), 11beta-hydroxylase (cyp11b), androgen receptor (arb) and estrogen receptors (era, erb1 and erb2) were assessed by qPCR prior and during sex differentiation. Canonical discriminant analysis (CDA), with length--as proxy for developmental stage--and cyp19a1a expression as predictors, was validated and used to reliably assign gonadal sex to fish sampled within and outside the TSP. Differences in cyp19a1a and cyp11b expression could be detected 1-month before the first signs of histological sex differentiation. Cyp19a1a and cyp11b were significantly higher in future females and males, respectively, and revealed as robust molecular markers to predict future ovarian and testicular differentiation. In contrast, no association between phenotypic sex and arb, era, erb1 and erb2 expression was found, suggesting that these genes do not contribute to the differentiation of a particular sex. The CDA-based approach implemented here could be used to sex undifferentiated animals in species where genetic sex cannot be known owing to the lack of simple sex determining systems, as it is the case of many fish and reptiles with or without temperature-dependent sex determination, and provide a useful tool to relate gene expression and phenotypic sex.

Cloning and expression of candidate sexual development genes in the cane toad (Bufo marinus)

The development of the reproductive system in bufonids (true toads) is unique in several respects: sexual differentiation occurs later than in other anurans, and toads develop a Bidder's organ, a rudimentary ovary that can be manipulated in males to produce mature oocytes. To illuminate the genesis of this unusual reproductive system, we isolated from the cane toad (Bufo marinus) the orthologues of several known vertebrate sex-determining genes, determined their primary structure, and studied their expression by reverse transcriptase-polymerase chain reaction and in situ hybridization of tissue sections. We report here that cane toad Sox9, Dmrt1, and p450aromatase (Cyp19a1) are highly homologous to their counterparts in other vertebrates. They show profiles of expression that generally follow patterns observed in other taxa, but with some novel features. Our data suggest that these genes likely play key roles in sex determination and early gonad development in bufonids.

Gonadal sex differentiation and expression of Sox9a2, Dmrt1, and Foxl2 in Oryzias luzonensis

Oryzias luzonensis is closely related to the medaka, O. latipes. The sex of both species is determined by an XX-XY system. However, the testis determining gene (DMY/Dmrt1bY) found in O. latipes does not exist in O. luzonensis. Instead, a different gene is thought to act as a testis determining gene. In this study, we focused the gonadal sex differentiation process in O. luzonensis under different testis determining gene. First, we observed the gonadal development of O. luzonensis histologically. We then analyzed the expression of Sox9a2/Sox9b, Dmrt1, and Foxl2 during early development. Our results suggest that the sexual differentiation of germ cells in O. luzonensis is initiated later than in O. latipes. However, the timing of the sexual differentiation of the supporting cell linage is similar between the species.

Different sox17 transcripts during sex differentiation in sea bass, Dicentrarchus labrax

Sox genes participate in several developmental processes, including sex determination and differentiation. In this study, the genomic structure of sox17 was characterized in the sea bass (sb). Two transcripts, one producing a normal protein (sb Sox17) and another producing a truncated protein (sb t-Sox17) were detected. A third, novel transcript, originated by intron retention (sb i-sox17) was also observed. Sb sox17 was widely distributed, whereas sb i-sox17 was predominantly found in skin and brain. In gonads, sb sox17 expression first increased at 150 days of age, coinciding with the onset of sex differentiation. At 250 days and onwards, sb sox17 expression was significantly higher in females, and mRNA levels correlated with those of gonadal aromatase. Thus, this study provides the first evidence for the presence of alternative splicing by intron retention in a Sox17 gene, and for sex-related differences in expression, implicating sox17 in ovarian development and function in fish.

Gonad morphogenesis in vertebrates: divergent means to a convergent end

A critical element of successful sexual reproduction is the generation of sexually dimorphic adult reproductive organs, the testis and ovary, which produce functional gametes. Examination of different vertebrate species shows that the adult gonad is remarkably similar in its morphology across different phylogenetic classes. Surprisingly, however, the cellular and molecular programs employed to create similar organs are not evolutionarily conserved. We highlight the mechanisms used by different vertebrate model systems to generate the somatic architecture necessary to support gametogenesis. In addition, we examine the different vertebrate patterns of germ cell migration from their site of origin to colonize the gonad and highlight their roles in sex-specific morphogenesis. We also discuss the plasticity of the adult gonad and consider how different genetic and environmental conditions can induce transitions between testis and ovary morphology.

Expression profiles for six zebrafish genes during gonadal sex differentiation

BACKGROUND

The mechanism of sex determination in zebrafish is largely unknown and neither sex chromosomes nor a sex-determining gene have been identified. This indicates that sex determination in zebrafish is mediated by genetic signals from autosomal genes. The aim of this study was to determine the precise timing of expression of six genes previously suggested to be associated with sex differentiation in zebrafish. The current study investigates the expression of all six genes in the same individual fish with extensive sampling dates during sex determination and -differentiation.

RESULTS

In the present study, we have used quantitative real-time PCR to investigate the expression of ar, sox9a, dmrt1, fig alpha, cyp19a1a and cyp19a1b during the expected sex determination and gonadal sex differentiation period. The expression of the genes expected to be high in males (ar, sox9a and dmrt1a) and high in females (fig alpha and cyp19a1a) was segregated in two groups with more than 10 times difference in expression levels. All of the investigated genes showed peaks in expression levels during the time of sex determination and gonadal sex differentiation. Expression of all genes was investigated on cDNA from the same fish allowing comparison of the high and low expressers of genes that are expected to be highest expressed in either males or females. There were 78% high or low expressers of all three "male" genes (ar, sox9a and dmrt1) in the investigated period and 81% were high or low expressers of both "female" genes (fig alpha and cyp19a1a). When comparing all five genes with expected sex related expression 56% show expression expected for either male or female. Furthermore, the expression of all genes was investigated in different tissue of adult male and female zebrafish.

CONCLUSION

In zebrafish, the first significant peak in gene expression during the investigated period (2-40 dph) was dmrt1 at 10 dph which indicates involvement of this gene in the early gonadal sex differentiation of males.

Sexual dimorphic expression of DMRT1 and Sox9a during gonadal differentiation and hormone-induced sex reversal in the teleost fish Nile tilapia (Oreochromis niloticus)

We examined the expression profiles of tDMRT1 and Sox9a during gonadal sex differentiation and hormone-induced sex reversal. tDMRT1 was detected in the gonial germ-cell-surrounding cells in XY fry specifically before the appearance of any signs of morphological sex differentiation, that is, sex differences in germ cell number and histogenesis, such as differentiation into intratesticular efferent duct or ovarian cavity. The signals became localized in the Sertoli and epithelial cells comprising the efferent duct during gonadal differentiation. After the induction of XY sex reversal with estrogen, tDMRT1 decreased and then disappeared completely. In contrast, tDMRT1 was expressed in the germ-cell-surrounding cells in XX sex reversal with androgen. On the other hand, Sox9a did not show sexual dimorphism before the appearance of sex differences in histogenesis and was not expressed in the efferent duct in the testis. These results suggest that tDMRT1 is a superior testicular differentiation marker in tilapia.

Global gene expression profiling of androgen disruption in Qurt strain medaka

Androgen disrupting chemicals (ADCs) are endocrine disrupting chemicals (EDCs) that mimic or antagonize the effect of physiological androgens. Microarray-based detection of altered gene expression can be used as a biomarker of EDC exposure. Therefore, the purpose of this study was to identify and compare gene expression profiles of the androgen 11-ketotestosterone (11-KT), the antiandrogen flutamide (FLU), and the antiandrogenic fungicide vinclozolin (VIN), on Qurt medaka (Oryzias latipes). Biologically effective concentrations for 11-KT (100 microg/L), VIN (100 microg/L), and FLU (1000 microg/L) determined in range-finding studies were used for exposures. The oligonucleotide microarray included 9379 probes for EDC-affected genes, medaka cDNAs, sequences from the medaka genome project, and the UniGene database. We found that treatment with FLU, VIN, and 11-KT caused significant (false discovery rate = 0.01) differential expression of at least 87, 82, and 578 genes, respectively. Two sets of responsive genes are associated to vertebrate sex differentiation and growth, and 50 genes were useful in discriminating between ADC classes. The discriminating capacity was confirmed by a remarkable similarity of the antiandrogenic expression profiles of VIN and FLU, which were distinct from the androgenic profile of 11-KT. Gene expression profiles characterized in this study allow for reliable screening of ADC activity.

Characterization of early molecular sex differentiation in rainbow trout, Oncorhynchus mykiss

Early differentiation in rainbow trout gonads was investigated by expression profiling and in situ hybridization (ISH). Expression of cyp19a1 and fst in females and sox9a1 in males were sexually dimorphic between 32 to 35 days post-fertilization (dpf). After 35 dpf, the differentiation proceeded with sexually dimorphic profiles for sox9a2, dmrt1, cyp11b2.1, amh in males and foxl2a, foxl2b, hsd3b1, inha in females. cyp17a1, cyp11a1, star, nr5a1b increased only after 40 dpf in both sexes with a slightly higher expression in females. cyp19a1 expression was localized in a cluster of somatic cells in the ventral side of female gonads, and sox9a2 and amh in somatic cells surrounding the germ cells, at 28 dpf and thereafter, both in male and female gonads. cyp11b2.1, cyp17a1, and cyp11a1 expressions were only detected in scattered somatic cells in males after 46 dpf. This confirms the early implication of cyp19a1 in trout ovarian differentiation and suggests that early testicular differentiation does not need androgen production.

Dax1 suppresses P450arom expression in medaka ovarian follicles

Dax1 is a member of an unusual orphan nuclear receptor family, and is known to regulate P450arom in mammals and is involved in sex differentiation in some vertebrates. To investigate whether Dax1 is involved in the regulation of the steroidogenic pathway for estrogen biosynthesis in medaka ovarian follicles, we isolated Dax1 cDNA from adult medaka ovaries and analyzed its expression pattern in medaka gonads. In adult ovaries, Dax1 mRNA was detected only in postvitellogenic follicles and was not detected in previtellogenic and vitellogenic follicles. In adult testis, Dax1 mRNA was not detected. We compared the expression pattern of Dax1 with that of Foxl2, Ad4BP/Sf-1, P450c17, and P450arom by in situ hybridization using adjacent sections. In contrast to Dax1 expression, these genes were co-expressed in vitellogenic follicles but were not detected in postvitellogenic follicles. Thus, in medaka ovarian follicles, Dax1 did not show any overlapping expression patterns against Foxl2, Ad4BP/Sf-1, P450c17, and P450arom. Moreover, co-transfection experiments demonstrated that Dax1 inhibits Ad4BP/Sf-1- and Foxl2-mediated P450arom expression. On the other hand, during early sex differentiation, Dax1 mRNA was not detected in both males and females. Our results suggest that Dax1 down-regulates Ad4BP/Sf-1- and Foxl2-mediated P450arom expression in medaka ovarian follicles.

Germ cells are essential for sexual dimorphism in the medaka gonad

To further elucidate the roles of germ cells in the sex differentiation of gonads, we have used the medaka, a teleost fish, to generate mutants that lack germ cells from the onset of gonadogenesis by the morpholino-mediated knockdown of cxcr4. The resulting germ-cell-deficient medaka show female-to-male sex reversal of their secondary sex characteristics, accompanied by increased levels of androgen and reduced levels of estrogen. A failure to maintain granulosa cells or estrogen-producing cells also occurs at early stages of sex differentiation in the cxcr4 morphants, before the initiation of gonadal morphogenesis. In contrast, androgen-producing cells are unaffected in germ-cell-deficient medaka of either sex. In addition, a single tube-like gonad that expresses male-specific genes is formed in these mutants irrespective of the genetic sex. Significantly, each of these mutant phenotypes occurs in a somatic cell-autonomous manner, suggesting that gonadal somatic cells are predisposed toward male development in the absence of germ cells. This highlights the importance of germ cells in the sexual dimorphism of the gonads.

A homologue of Sox11 predominantly expressed in the ovary of the orange-spotted grouper Epinephelus coioides

Sox, a family of genes related to the mammalian sex-determining region Y (SRY) gene, are found throughout the animal kingdom and regulate diverse developmental processes including sex determination. The full-length Sox11b cDNA was cloned from the ovary of the orange-spotted grouper Epinephelus coioides. This sequence is highly homologous to SOX11 of other species and contained the signature features of mammalian SOX11 homologues, except for the absence of Pro-Glu rich region and presence of two Ser-rich regions. Southern blot analysis suggested that there is likely a single copy of Sox11b gene in the genome of this fish. The mRNA expression of Sox11b was detected in a wide range of tissues except the blood cells, and its expression is especially abundant in the ovary. During embryogenesis and larval development, the mRNA levels of Sox11b were high except at the eyed stage. During 17alpha-methyltestosterone (MT)-induced precocious sex change, the mRNA levels of Sox11b in the gonads were decreased significantly. Together, these results indicated that Sox11b may be involved in the oogenesis, embryogenesis, larval development, and sex change of the orange-spotted grouper.

Sexual dimorphic expression of genes in gonads during early differentiation of a teleost fish, the Nile tilapia Oreochromis niloticus

The Nile tilapia, a gonochoristic teleost fish with an XX/XY sex-determining system, provides an excellent model for studying gonadal sex differentiation because genetic all-females and all-males are available. In this study, we used quantitative real-time RT-PCR to determine the precise timing of the gonadal expression of 17 genes thought to be associated with gonadal sex differentiation in vertebrates. Gonads were isolated from all-female and all-male tilapia before (5-15 days after hatching [dah]) and after (25-70 dah) morphological sex differentiation. The transcript of aromatase (cyp19a1a), an enzyme responsible for producing estradiol-17beta, was expressed only in XX gonads at 5 dah, with a marked elevation in expression thereafter. In contrast, mRNA expression of steroid 11beta-hydroxylase (cyp11b2), an enzyme responsible for the synthesis of 11-ketotestosterone (11-KT, a potent androgen in fish), was found in XY gonads from 35 dah only. These results, combined with the presence of transcripts for other steroidogenic enzymes and estrogen receptors in XX gonads at 5-7 dah, are consistent with our earlier suggestion that estradiol-17beta plays a critical role in ovarian differentiation in tilapia, whereas a role for 11-KT in testicular differentiation is questionable. A close relationship between the expression of foxl2, but not nr5a1 (Ad4BP/SF-1), and that of cyp19a1a in XX gonads suggests an important role for Foxl2 in the transcriptional regulation of cyp19a1a. Dmrt1 exhibited a male-specific expression in XY gonads from 6 dah onward, suggesting an important role for Dmrt1 in testicular differentiation. Sox9 and amh (anti-Mullerian hormone) showed a testis-specific expression, being evident only in the later stages of testicular differentiation. It is concluded that the sex-specific expression of foxl2 and cyp19a1a in XX gonads and dmrt1 in XY gonads during early gonadal differentiation (5-6 dah) is critical for undifferentiated gonads to differentiate into either the ovary or testis in the Nile tilapia.

Differential expression of anti-Müllerian hormone (amh) and anti-Müllerian hormone receptor type II (amhrII) in the teleost medaka

In mammals, the anti-Müllerian hormone (Amh) is responsible for the regression of the Müllerian ducts; therefore, Amh is an important factor of male sex differentiation. The amh gene has been cloned in various vertebrates, as well as in several teleost species. To date, all described species show a sexually dimorphic expression of amh during sex differentiation or at least in differentiated juvenile gonads. We have identified the medaka amh ortholog and examined its expression pattern. Medaka amh shows no sexually dimorphic expression pattern. It is expressed in both developing XY male and XX female gonads. In adult testes, amh is expressed in the Sertoli cells and in adult ovaries in granulosa cells surrounding the oocytes, like in mammals. To better understand the function of amh, we cloned the anti-Müllerian hormone receptor type II (amhrII) ortholog and compared its expression pattern with amh, aromatase (cyp19a1), and scp3. During gonad development, amhrII is coexpressed with medaka amh in somatic cells of the gonads and shows no sexually dimorphic expression. Only the expression level of the Amh type II receptor gene was decreased noticeably in adult female gonads. These results suggest that medaka Amh and AmhrII are involved in gonad formation and maintenance in both sexes.

Isolation and expression analysis of testicular type Sox9b in allotetraploid fish

We isolated a Sox9 homologue, termed Sox9b, from adult allotetraploids. On the basis of the HMG-box amino acid sequences, Sox9b can be categorized into the same subgroup of Sox-E proteins as SOX8, 9, and 10. Interestingly, Northern and Southern hybridization demonstrated that Sox9b was highly expressed in the testis but at lower levels in the heart and brain, while no expression of Sox9b mRNA was discovered in the ovary of adult allotetraploids. Two transcripts of Sox9 (2.1 kb and 1.7 kb) with overlapping expression were observed for the first time in teleosts. These results indicated that allotetraploid Sox9b might be involved in gonadal development of male allotetraploids. In addition, the diverse tissue-specific expression profiles of Sox9b provided significant molecular evidence for the lineage-specific subfunction partitioning of Sox9 genes.

Locating the barnacle settlement pheromone: spatial and ontogenetic expression of the settlement-inducing protein complex of Balanus amphitrite

Barnacles are prominent members of hard substratum benthic communities and their study has been important to advances in experimental ecology and contemporary ecological theory. Having recently characterized the cue to gregarious settlement of Balanus amphitrite, the settlement-inducing protein complex (SIPC), we use two polyclonal antibodies to examine the tissue distribution and ontogenetic expression of this glycoprotein. These antibodies were raised against two separate peptides located near the N- and C-termini of the SIPC and were used to detect the glycoprotein by western blotting and immunohistochemistry. By in situ hybridization we also show that the SIPC mRNA co-occurs with the expressed glycoprotein in the cuticles of both nauplius and cypris larval stages and the adult. In the larvae, the SIPC is expressed most strongly in the mouthparts and the hindgut of the stage 2 nauplius and in the thoracopods, antennules and bivalved carapace of the cyprid. In adult B. amphitrite, the expressed SIPC is present in protein extracts of the shell and in all organs that are lined by cuticular tissues. We suggest that the SIPC is produced by the epidermal cells that secrete the cuticle and discuss these observations with regard to earlier studies and the role of the SIPC as a contact pheromone.

Sox9b/sox9a2-EGFP transgenic medaka reveals the morphological reorganization of the gonads and a common precursor of both the female and male supporting cells

We have established an enhanced green fluorescent protein (EGFP) transgenic medaka line that mimics the expression of sox9b/sox9a2 to analyze the morphological reorganization of the gonads and characterize the sox9b-expressing cells during gonadal formation in this fish. After the germ cells have migrated into the gonadal areas, a cluster of EGFP-expressing cells in the single gonadal primordium was found to be separated by the somatic cells along the rostrocaudal axis and form the bilateral lobes. We observed in these transgenic fish that EGFP expression persists only in the somatic cells directly surrounding the germ cells. As sex differentiation proceeds, dmrt1 and foxl2 begin to be expressed in the EGFP-expressing cells in the XY and the XX gonads, respectively. This indicates that the sox9b-expressing cells reorganize into two lobes of the gonad and then differentiate into Sertoli or granulosa cells, as common precursors of the supporting cells. Hence, our sox9b-EGFP medaka system will be useful in future studies of gonadal development.

Identification and lineage tracing of two populations of somatic gonadal precursors in medaka embryos

The gonad contains two major cell lineages, germline and somatic cells. Little is known, however, about the somatic gonadal cell lineage in vertebrates. Using fate mapping studies and ablation experiments in medaka fish (Oryzias latipes), we determined that somatic gonadal precursors arise from the most posterior part of the sdf-1a expression domain in the lateral plate mesoderm at the early segmentation stage; this region has the properties of a gonadal field. Somatic gonadal precursors in this field, which continuously express sdf-1a, move anteriorly and medially to the prospective gonadal area by convergent movement. By the stage at which these somatic gonadal precursors have become located adjacent to the embryonic body, the precursors no longer replace the surrounding lateral plate mesoderm, becoming spatially organized into two distinct populations. We further show that, prior to reaching the prospective gonadal area, these populations can be distinguished by expression of either ftz-f1 or sox9b. These results clearly indicate that different populations of gonadal precursors are present before the formation of a single gonadal primordium, shedding new light on the developmental processes of somatic gonadal cell and subsequent sex differentiation.