DM Domain Research Articles

Transcriptional variants of Dmrt1 and expression of four Dmrt genes in the blunt snout bream, Megalobrama amblycephala

Doublesex and Mab3 related transcription factor (DMRT), characterized by a conserved DM domain, function as sex-related transcription factors and also play critical roles in ontogenesis. In this study, 4 Dmrt genes in the blunt snout bream, Megalobrama amblycephala, were identified, characterized and their mRNA expression in different adult organs, during embryogenesis and gonadal development in larvae were determined by quantitative real time PCR. There are 4 Dmrt1 isoforms in the M. amblycephala genome, which were expressed highly in the testis and weakly in the ovary. The complete cDNAs of the M. amblycephala Dmrt2a, Dmrt2b and Dmrt3 were predicted to encode 510, 328 and 449 amino acids, respectively. The M. amblycephala Dmrt2a mRNA peaked at 11hpf (hour post fertilizing) during early embryonic stages, while Dmrt2b was highly expressed during late embryonic stages. Both the M. amblycephala Dmrt2a and Dmrt2b were expressed highly in the gill and exhibited a sexually dimorphic expression pattern. The M. amblycephala Dmrt3 was expressed highly in the gill, muscle and brain, at 40dph (day post hatching) during early development and at stage V in the testis during gonadal development. All fish Dmrts except Dmrt5 were found in the M. amblycephala genome. The observed expression patterns of these Dmrts in developing embryos and larvae, as well as different adult organs indicate conserved sexual or extragonadal functions of the Dmrts through evolution.

A sex-determining interaction

DNA Binding Across much of the animal kingdom, DMRT proteins are involved in regulating sexual development. In humans, DMRT1 both activates a male sex-determining gene and deactivates female sex-determining genes. Murphy et al. report a crystal structure showing three DNA binding DM domains, each comprising a zinc binding module followed by a recognition helix, bound to target DNA. Recognition helices from two domains lie antiparallel in a widened major groove. They find that DMRT1 can bind as a dimer, trimer, or tetramer in vitro and in vivo, with DNA sequence and shape dictating the binding mode. A mutation that causes male-to female sex reversal in humans reduces binding affinity and interferes with the binding stoichiometry of wild-type DMRT1. Nat. Struct. Mol. Biol. 22 , 442 (2015).

The roles of Dmrt (Double sex/Male-abnormal-3 Related Transcription factor) genes in sex determination and differentiation mechanisms: Ubiquity and diversity across the animal kingdom

The Dmrt (Double sex/Male-abnormal-3 Related Transcription factor) genes have been intensively studied because they represent major transcription factors in the pathways governing sex determination and differentiation. These genes have been identified in animal groups ranging from cnidarians to mammals, and some of the genes functionally studied. Here, we propose to analyze (i) the presence/absence of various Dmrt gene groups in the different taxa across the animal kingdom; (ii) the relative expression levels of the Dmrt genes in each sex; (iii) the specific spatial (by organ) and temporal (by developmental stage) variations in gene expression. This review considers non-mammalian animals at all levels of study (i.e. no particular importance is given to animal models), and using all types of sexual strategy (hermaphroditic or gonochoric) and means of sex determination (i.e. genetic or environmental). To conclude this global comparison, we offer an analysis of the DM domains conserved among the different DMRT proteins, and propose a general sex-specific pattern for each member of the Dmrt gene family.

Female-to-male sex reversal in mice caused by transgenic overexpression of Dmrt1.

Genes related to Dmrt1, which encodes a DNA-binding DM domain transcription factor, act as triggers for primary sex determination in a broad range of metazoan species. However, this role is fulfilled in mammals by Sry, a newly evolved gene on the Y chromosome, such that Dmrt1 has become dispensable for primary sex determination and instead maintains Sertoli cell phenotype in postnatal testes. Here, we report that enforced expression of Dmrt1 in XX mouse fetal gonads using a Wt1-BAC transgene system is sufficient to drive testicular differentiation and male secondary sex development. XX transgenic fetal gonads showed typical testicular size and vasculature. Key ovarian markers, including Wnt4 and Foxl2, were repressed. Sertoli cells expressing the hallmark testis-determining gene Sox9 were formed, although they did not assemble into normal testis cords. Other bipotential lineages differentiated into testicular cell types, including steroidogenic fetal Leydig cells and non-meiotic germ cells. As a consequence, male internal and external reproductive organs developed postnatally, with an absence of female reproductive tissues. These results reveal that Dmrt1 has retained its ability to act as the primary testis-determining trigger in mammals, even though this function is no longer normally required. Thus, Dmrt1 provides a common thread in the evolution of sex determination mechanisms in metazoans.

Molecular Cloning and Expression Pattern of <italic>Dmrt1</italic> and Its Expression Change in Sex Reversal in <italic>Pelodiscus sinensis</italic>

In many vertebrate species, <italic>Dmrt1</italic> gene is required for male sexual differentiation. In this study, the mRNA and protein expression of <italic>Dmrt1</italic> gene and its cellular localization in gonads of different developmental stages of both sexes were examined to investigate the involvement of <italic>Dmrt1</italic> in sexual differentiation in <italic>Pelodiscus sinensis</italic>. RACE results showed that the complete cDNA sequence of <italic>P. sinensis</italic> <italic>Dmrt1</italic> was composed of 230 bp of 5′ un-translated region, 1072 bp of 3′ un-translated region and 1107 bp of open reading frame, bearing a highly conserved DM domain, which encodes 368 amino acids. Real-Time PCR and immunofluorescence analysis revealed that <italic>Dmrt1</italic> gene initiated expression in male embryonic gonad of stage 16 before gonadal differentiation, prior to <italic>Sox9</italic> and <italic>Amh</italic> gene. During the gonadal development, Dmrt1 protein localized in the nuclei of pre-sertoli cells, however, no Dmrt1 signal was detected in female gonad. Moreover, <italic>Dmrt1</italic> expression was significantly decreased in estrogen-induced male to female sex reversal. Whereas, <italic>Dmrt1</italic> was trigged to express in aromatase inhibitor-induced female to male sex reversal. In conclusion, this study indicates that <italic>Dmrt1</italic> gene is a male-specific gene and participates in the male gonadal development, which is likely to play a key role during primary male sex determination in <italic>P. sinensis</italic>.

The low expression of Dmrt7 is associated with spermatogenic arrest in cattle-yak.

Dmrt7 is a member of the DM domain family of genes. Dmrt7 deficiency is also a strong candidate as a cause for male cattle-yak infertility, as it is regarded as essential for male spermatogenesis, between the pachynema and diplonema stages. In our study, the coding region sequence of yak and cattle-yak Dmrt7 was cloned by molecular cloning techniques, and the sequence, conserved domains, functional sites, and secondary and tertiary structures of the Dmrt7-encoded protein were predicted and analyzed using bioinformatics methods. The coding region sequences of the Dmrt7 gene, encoding 370 amino acids, were consistent in yak and cattle-yak. The protein encoded by yak and cattle-yak Dmrt7 contains a DM domain. We detected Dmrt7 mRNA expression in testis, but not in any other tissue. Dmrt7 mRNA and protein expression was significantly higher in testis of cattle and yak than that in cattle-yak (p<0.01). Histological analysis indicated that seminiferous tubules in male cattle-yak were highly vacuolated and contained primarily Sertoli cells and spermatogonia, while those of cattle and yak contained abundant primary spermatocytes. Male cattle-yak testis contained a significantly larger number of apoptotic cells than those in cattle and yak assessed by terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) analysis. The accumulation of SCP3-positive spermatocytes indicated the arrest of spermatogenesis at the pachynema stage in the cattle-yak. These results suggest low levels of Dmrt7 expression lead to male sterility in cattle-yak. The molecular function of Dmrt7 and the regulation of its expression warrant need to be examined in future studies.

Identification of three doublesex genes in the monogonont rotifer Brachionus koreanus and their transcriptional responses to environmental stressor-triggered population growth retardation.

Doublesex and Mab-3-related transcription factor (Dmrt) gene family members have rarely been identified or characterized in aquatic invertebrates. In this study, we identified and characterized three DMdomain-containing genes - Dmrt11E, Dmrt93B, and Dmrt99B - in the monogonont rotifer, Brachionus koreanus. DMdomains of the proteins encoded by the B.koreanus Dmrt (Bk-Dmrt) genes had high similarities to DM domains of other invertebrate species. To understand the potential effects of environmental stressors on the transcriptional expression of Dmrt genes in rotifers, we exposed B.koreanus to a wide range of UV-B radiation and different concentrations of benzo[a]pyrene (B[a]P) over different time courses. Transcript levels of all Bk-Dmrt genes decreased significantly in response to relatively high doses of UV-B irradiation, and were also downregulated in response to exposure to UV-B radiation over time. Transcript levels of all Bk-Dmrt genes were downregulated in response to B[a]P exposure for 24h. This decrease in expression of all Bk-Dmrt genes was concomitant with the growth retardation induced by UV-B and B[a]P exposure. We concluded that both environmental stressors have detrimental effects on transcriptional regulation of all Bk-Dmrt genes, especially relatively high doses of these stressors, leading to growth retardation. However, further studies are required to better understand the potential role of Dmrt genes in environmental stressor-triggered growth retardation in the rotifer B.koreanus.

Molecular Cloning and Sexually Dimorphic Expression of Two Dmrt Genes in the Giant Freshwater Prawn, Macrobrachium rosenbergii

The molecular mechanism of sex determination changed rapidly during evolution among phyla. One exception is the Dmrt (doublesex and mab-3 related transcription factor) family gene, which is widely conserved for its involvement in sex development from invertebrates to humans. In this study, we identified two DM-domain genes in the giant freshwater prawn, Macrobrachium rosenbergii, which we named MroDmrt11E and MroDmrt99B according to their high similarities and phylogenetically close relationships with arthropod Dmrt11E and Dmrt99B genes, respectively. Amino acid alignments and structural prediction uncovered conservation and putative active sites of their DM domains. Realtime PCR analysis exhibits a sexually dimorphic and embryonic development-dependent expression pattern of both genes. The transcription of both MroDmrt11E and MroDmrt99B was prominent in testis, and both mRNAs were localized in spermatogonia and spermatozoa during spermatogenesis. RNAi-targeting MroDmrt99B showed no effect on several male-reproduction related genes while the MroDmrt11E RNAi induced a significant decrease of the transcript of Iag, an important regulatory gene in the male determination mechanism of the prawn. The complicated expression profiles of Dmrt family genes and closely related subfamily members may provide clues of their rapid evolution and multi-functionality. Our study will contribute to understanding mechanistic and evolutionary dynamics of Dmrt family genes in metazoan bisexual development and embryogenesis.

The development of sexual dimorphism: studies of the Caenorhabditis elegans male.

Studies of the development of the Caenorhabditis elegans male have been carried out with the aim of understanding the basis of sexual dimorphism. Postembryonic development of the two C. elegans sexes differs extensively. Development along either the hermaphrodite or male pathway is specified initially by the X to autosome ratio. The regulatory events initiated by this ratio include a male-determining paracrine intercellular signal. Expression of this signal leads to different consequences in three regions of the body: the nongonadal soma, the somatic parts of the gonad, and the germ line. In the nongonadal soma, activity of the key Zn-finger transcription factor TRA-1 determines hermaphrodite development; in its absence, the male pathway is followed. Only a few genes directly regulated by TRA-1 are currently known, including members of the evolutionarily conserved, male-determining DM domain Zn-finger transcription factors. In the somatic parts of the gonad and germ line, absence of TRA-1 activity is not sufficient for full expression of the male pathway. Several additional transcription factors involved have been identified. In the germ line, regulatory genes for sperm development that act at the level of RNA in the cytoplasm play a prominent role.

Identification and expression analysis of a doublesex1 gene in Daphnia pulex during different reproductive stages.

The gene doublesex (dsx) has shown deep conservation in the sex determination in many organisms. Environmental stimuli initiate a switch in the reproductive strategy of Daphnia pulex from asexual to sexual reproduction; however, occasionally, changes in environmental conditions will not lead to this transition. So study genetic responses to environmental stimuli and the molecular basis for the switch of reproductive stages are urgently needed. Therefore, we isolated and sequenced a D. pulex doublesex1 gene (Dpdsx1) and analyzed its expression and location by quantitative polymerase chain reaction (qPCR) and whole-mount in situ hybridization in D. pulex during different stages of reproduction. The predicted amino acid sequence has 335 amino acids that contained one DM domain and one dimerization domain, which is characteristic of insect orthologs of Dsx. Real-time PCR showed that Dpdsx1 expression decreased significantly (P < 0.05) in different reproductive stages in the following order: male, parthenogenetic female, ephippial female, resting egg, and juvenile female. Whole-mount in situ hybridization revealed that Dpdsx1 is expressed in the first antennae, first thoracic limb and compound eye in males, whereas expression levels in the corresponding sites of parthenogenetic and ephippial females were relatively weak. Dpdsx1 could not be detected in the gonads of males or ephippial and parthenogenetic females. Taken together, these different reproductive stages' and sex specific expression patterns are regulated temporally and spatially. We speculate that Dpdsx1 may involve in switching different stages of reproduction and in sexual differentiation in D. pulex.

Characterization of the Dmrt1 gene in the black rockfish Sebastes schlegeli revealed a remarkable sex-dimorphic expression

The Dmrt genes encode a large family of transcription factors with a conserved zinc finger-like DNA-binding DM domain. The function of Dmrt1, one of the family members, in sexual development has been well studied in invertebrates and vertebrates. In the present study, the full-length cDNA of Dmrt1 was isolated from the testis of Sebastes schlegeli. The full-length cDNA of S. schlegeli Dmrt1 (SsDmrt1) was 1,587bp and contained a 189-bp 5' UTR, a 489-bp 3' UTR and a 909-bp open reading frame, which encoded 302 amino acids with a conserved DM domain and an male-specific motif domain. Phylogenetic analysis showed the evolutionary relationships of SsDmrt1 with other known Dmrt genes in fish and tetrapods. Several transcriptional factor-binding sites in the 5' promoter were identified that might regulate SsDmrt1 expression. Quantitative real-time PCR analysis indicated that SsDmrt1 was expressed in all of the inspected larval developmental stages from 1 to 35days after birth and that the level of expression gradually decreased. The expression of SsDmrt1 in adult gonads was sexually dimorphic with extremely high expression in the testis, but very low expression in the ovary. No expression was detected in other tissues. Using in situ hybridization, we demonstrated that SsDmrt1 was specifically expressed in the germ cells of both the testis and the ovary. Thus, our results suggest that SsDmrt1 may have an important role in the differentiation of both the testis and the ovary of S. schlegeli.

Molecular identification of dmrt2 and dmrt5 and effect of sex steroids on their expressions in Chlamys nobilis

The dmrt (double-sex and mab-3-related transcription factor) gene family, characterized by a highly conserved zinc finger-like DNA-binding motif known as the DM domain, plays important roles in sex differentiation and sexual development. To better understand the role of dmrt on the sexual development in Chlamys nobilis, 1183 bp encoding cDNAs for dmrt2 and 2362 bp encoding cDNAs for dmrt5 have been cloned and functionally characterized. Dmrt2 and dmrt5 display significant homologies to DMRT2 cluster and DMRT5 cluster, respectively, and exhibit all the typical features of dmrt family. Real-time PCR analyses show that dmrt2 was expressed exclusively in gonads and dmrt5 distributed widely in tissues. Both of them were expressed at all developmental stages examined and peaked at blastula stage. Dmrt2 expression peaked at resting stage in the female gametogenetic cycle, and mature stage in male gonadal development. Dmrt5 expression peaked at resting stage in the female gametogenetic cycle and no significant differences were observed in male gonadal development. Expression of dmrt2 and dmrt5 of C. nobilis at spawning stage was upregulated by different concentration of MT (17 alpha-methyltestosterone) injected into the male and E-2 (17 beta-estradiol) injected into the female, at different time after treatment, and even different duration of function. These results implied that dmrt2 is more likely to be involved in playing a functional role in male gonadal development or maintenance of gonadal function than dmrt5 and dmrt5 may be involved in other biological processes besides gonadal development in C. nobilis. (C) 2014 Elsevier B.V. All rights reserved.

A sex-specific transcription factor controls male identity in a simultaneous hermaphrodite

Evolutionary transitions between hermaphroditic and dioecious reproductive states are found in many groups of animals. To understand such transitions, it is important to characterize diverse modes of sex determination utilized by metazoans. Currently, little is known about how simultaneous hermaphrodites specify and maintain male and female organs in a single individual. Here we show that a sex-specific gene, Smed-dmd-1 encoding a predicted doublesex/male-abnormal-3 (DM) domain transcription factor, is required for specification of male germ cells in a simultaneous hermaphrodite, the planarian Schmidtea mediterranea. dmd-1 has a male-specific role in the maintenance and regeneration of the testes and male accessory reproductive organs. In addition, a homologue of dmd-1 exhibits male-specific expression in Schistosoma mansoni, a derived, dioecious flatworm. These results demonstrate conservation of the role of DM domain genes in sexual development in lophotrochozoans and suggest one means by which modulation of sex-specific pathways can drive the transition from hermaphroditism to dioecy.

Molecular cloning of doublesex genes of four cladocera (water flea) species

BackgroundThe gene doublesex (dsx) is known as a key factor regulating genetic sex determination in many organisms. We previously identified two dsx genes (DapmaDsx1 and DapmaDsx2) from a freshwater branchiopod crustacean, Daphnia magna, which are expressed in males but not in females. D. magna produces males by parthenogenesis in response to environmental cues (environmental sex determination) and we showed that DapmaDsx1 expression during embryonic stages is responsible for the male trait development. The D. magna dsx genes are thought to have arisen by a cladoceran-specific duplication; therefore, to investigate evolutionary conservation of sex specific expression of dsx genes and to further assess their functions in the environmental sex determination, we searched for dsx homologs in four closely related cladoceran species.ResultsWe identified homologs of both dsx genes from, D. pulex, D. galeata, and Ceriodaphnia dubia, yet only a single dsx gene was found from Moina macrocopa. The deduced amino acid sequences of all 9 dsx homologs contained the DM and oligomerization domains, which are characteristic for all arthropod DSX family members. Molecular phylogenetic analysis suggested that the dsx gene duplication likely occurred prior to the divergence of these cladoceran species, because that of the giant tiger prawn Penaeus monodon is rooted ancestrally to both DSX1 and DSX2 of cladocerans. Therefore, this result also suggested that M. macrocopa lost dsx2 gene secondarily. Furthermore, all dsx genes identified in this study showed male-biased expression levels, yet only half of the putative 5’ upstream regulatory elements are preserved in D. magna and D. pulex.ConclusionsThe all dsx genes of five cladoceran species examined had similar amino acid structure containing highly conserved DM and oligomerization domains, and exhibited sexually dimorphic expression patterns, suggesting that these genes may have similar functions for environmental sex determination in cladocerans.

Just how conserved is vertebrate sex determination?

Sex determination in vertebrate embryos has long been equated with gonadal differentiation into testes or ovaries. This view has been challenged over the years by reports of somatic sexual dimorphisms pre-dating gonadal sex differentiation. The recent finding that sex determination in birds is likely to be partly cell autonomous has again called for a broader definition of sex determination. Inherent sexual differentiation in each and every cell may apply widely among vertebrates, and may involve more than one "master sex gene" on a sex chromosome. At the gonadal level, key genes required for proper sexual differentiation are conserved among vertebrates, but their relative positions in the ovarian and testicular cascades differ. We illustrate these differences by comparing key sex genes in fishes versus birds and mammals, with emphasis on DM domain genes and the SOX9-AMH pathway in the testis and the FOXL2-Aromatase pathway in the ovary. Such comparisons facilitate the identification of ancient versus derived genes involved in gonadal sex determination. The data indicate that vertebrate sex-determining cascades are not as conserved as once thought.

Expanding roles for the evolutionarily conserved Dmrt sex transcriptional regulators during embryogenesis.

Dmrt genes encode a large family of transcription factors characterized by the presence of a DM domain, an unusual zinc finger DNA binding domain. While Dmrt genes are well known for their important role in sexual development in arthropodes, nematodes and vertebrates, several new findings indicate emerging functions of this gene family in other developmental processes. Here, we provide an overview of the evolution, structure and mechanisms of action of Dmrt genes. We summarize recent findings on their function in sexual regulation and discuss more extensively the role played by these proteins in somitogenesis and neural development.

The Xenopus doublesex-related gene Dmrt5 is required for olfactory placode neurogenesis

The Dmrt (doublesex and mab-3 related transcription factor) genes encode a large family of evolutionarily conserved transcription factors whose function in sex specific differentiation has been well studied in all animal lineages. In vertebrates, their function is not restricted to the developing gonads. For example, Xenopus Dmrt4 is essential for neurogenesis in the olfactory system. Here we have isolated and characterized Xenopus Dmrt5 and found that it is coexpressed with Dmrt4 in the developing olfactory placodes. As Dmrt4, Dmrt5 is positively regulated in the ectoderm by neural inducers and negatively by proneural factors. Both Dmrt5 and Dmrt4 genes are also activated by the combined action of the transcription factor Otx2, broadly transcribed in the head ectoderm and of Notch signaling, activated in the anterior neural ridge. As for Dmrt4, knockdown of Dmrt5 impairs neurogenesis in the embryonic olfactory system and in neuralized animal caps. Conversely, its overexpression promotes neuronal differentiation in animal caps, a property that requires the conserved C-terminal DMA and DMB domains. We also found that the sea anenome Dmrt4/5 related gene NvDmrtb also induces neurogenesis in Xenopus animal caps and that conversely, its knockdown in Nematostella reduces elav-1 positive neurons. Together, our data identify Dmrt5 as a novel important regulator of neurogenesis whose function overlaps with that of Dmrt4 during Xenopus olfactory system development. They also suggest that Dmrt may have had a role in neurogenesis in the last common ancestor of cnidarians and bilaterians.

The Mammalian DM Domain Transcription Factor Dmrta2 Is Required for Early Embryonic Development of the Cerebral Cortex

Development of the mammalian telencephalon is precisely organized by a combination of extracellular signaling events derived from signaling centers and transcription factor networks. Using gene expression profiling of the developing mouse dorsal telencephalon, we found that the DM domain transcription factor Dmrta2 (doublesex and mab-3-related transcription factor a2) is involved in the development of the dorsal telencephalon. Consistent with its medial-high/lateral-low expression pattern in the dorsal telencephalon, Dmrta2 null mutants demonstrated a dramatic reduction in medial cortical structures such as the cortical hem and the choroid plexus, and a complete loss of the hippocampus. In this mutant, the dorsal telencephalon also showed a remarkable size reduction, in addition to abnormal cell cycle kinetics and defective patterning. In contrast, a conditional Dmrta2 deletion in the telencephalon, which was accomplished after entry into the neurogenic phase, resulted in only a slight reduction in telencephalon size and normal patterning. We also found that Dmrta2 expression was decreased by a dominant-negative Tcf and was increased by a stabilized β-catenin form. These data suggest that Dmrta2 plays pivotal roles in the early development of the telencephalon via the formation of the cortical hem, a source of Wnts, and also in the maintenance of neural progenitors as a downstream of the Wnt pathway.

414 Screening Developmental Domains In Preterm Children: Diagnostic Validity Of “Parents’ Evaluation Of Developmental Status: Developmental Milestones” (PEDS:DM) Assessment Level

Background/aimsVery preterm children (VPT-born < 29 weeks gestation) are at high risk for delay across a range of developmental domains. The diagnostic utility of the Parents’ Evaluation of Developmental Status:...

Sex dimorphic expression of five dmrt genes identified in the Atlantic cod genome. The fish-specific dmrt2b diverged from dmrt2a before the fish whole-genome duplication

The Doublesex and Mab-3 related transcription factors (Dmrt) are characterised by the zinc finger-like DM domain binding similar DNA sequences, but show different spatio-temporal expression patterns and functions throughout ontogenesis. Dmrt1 is the master regulator of sex determination in very distant metazoans, while Dmrt2 and Dmrt4 are of crucial importance in vertebrate somitogenesis and neurogenesis, respectively. To elucidate the evolutionary divergence of the fish dmrt genes, we examined the expression patterns and the chromosomal synteny of the five dmrt genes identified in the Atlantic cod genome. Quantitative PCR analyses of cod dmrt1, dmrt2a, dmrt3, dmrt4 and dmrt5 revealed distinct expression patterns in the embryo and larvae, and indicated conserved extragonadal functions during early development. Several dmrt genes seem to be involved in the sexual differentiation of gonads and brain, but the sex-dimorphic expression patterns differed substantially between teleosts, suggesting functional switch between Dmrt members. The dmrt2a–dmrt3–dmrt1 cluster was found to be located in a conserved syntenic region, and the flanking genes have become duplicated in teleosts and are closely linked in a paralogous region lacking the dmrt cluster. Similarly, the region containing the fish-specific dmrt2b gene was found to have a paralogous region without a dmrt2b duplicate in a separate linkage group in the teleost genomes. We propose that the teleost segments paralogous to the dmrt2a- and dmrt2b regions, respectively, were formed through the fish-specific whole genome duplication (3R), while dmrt2a and dmrt2b originated from the second round (2R) of whole genome duplication of the ancestral dmrt2. The dmrt2b paralog seems to have been lost in Atlantic cod as in tetrapods and may be a pseudogene in pufferfish, while dmrt2a and dmrt2b have acquired different functions in zebrafish. Contrasting with the retained duplicates of dmrt flanking genes, the massive losses of dmrt duplicates in the vertebrate tetraploidizations suggest that their functions are exquisitely sensitive to gene dosage.