Expression pattern of dmrt4 from olive flounder (Paralichthys olivaceus) in adult gonads and during embryogenesis

DMRT Transcription Factors in the Control of Nervous System Sexual Differentiation

Sexual phenotypic differences in the nervous system are one of the most prevalent features across the animal kingdom. The molecular mechanisms responsible for sexual dimorphism throughout metazoan nervous systems are extremely diverse, ranging from intrinsic cell autonomous mechanisms to gonad-dependent endocrine control of sexual traits, or even extrinsic environmental cues. In recent years, the DMRT ancient family of transcription factors has emerged as being central in the development of sex-specific differentiation in all animals in which they have been studied. In this review, we provide an overview of the function of Dmrt genes in nervous system sexual regulation from an evolutionary perspective.

Comparative Genomics Studies on the dmrt Gene Family in Fish

Doublesex and mab-3-related transcription factor (dmrt) genes are widely distributed across various biological groups and play critical roles in sex determination and neural development. Here, we applied bioinformatics methods to exam cross-species changes in the dmrt family members and evolutionary relationships of the dmrt genes based on genomes of 17 fish species. All the examined fish species have dmrt1–5 while only five species contained dmrt6. Most fish harbored two dmrt2 paralogs (dmrt2a and dmrt2b), with dmrt2b being unique to fish. In the phylogenetic tree, 147 DMRT are categorized into eight groups (DMRT1–DMRT8) and then clustered in three main groups. Selective evolutionary pressure analysis indicated purifying selections on dmrt1–3 genes and the dmrt1–3–2(2a) gene cluster. Similar genomic conservation patterns of the dmrt1–dmrt3–dmrt2(2a) gene cluster with 20-kb upstream/downstream regions in fish with various sex-determination systems were observed except for three regions with remarkable diversity. Synteny analysis revealed that dmrt1, dmrt2a, dmrt2b, and dmrt3–5 were relatively conserved in fish during the evolutionary process. While dmrt6 was lost in most species during evolution. The high conservation of the dmrt1–dmrt3–dmrt2(2a) gene cluster in various fish genomes suggests their crucial biological functions while various dmrt family members and sequences across fish species suggest different biological roles during evolution. This study provides a molecular basis for fish dmrt functional analysis and may serve as a reference for in-depth phylogenomics.

Identification of candidate piRNAs in the gonads of Paralichthys olivaceus (Japanese flounder)

Piwi-interacting RNA (piRNA) plays an important role in the gonadal development and maintenance of Teleostei. In this study, piRNA libraries derived from the adult gonads of Japanese flounder (Paralichthys olivaceus) were generated using next-generation sequencing technology. Using zebrafish piRNAs as a reference, 5 865 unique candidate piRNAs were identified; 289 candidate piRNA clusters (PRCs) were generated from the above piRNAs. Among the isolated candidate PRCs, a total of 38 ovary-specific, 45 ovary-bias, 24 testis-specific, and 131 testis-bias PRCs were found. The relative expression levels of seven PRCs were validated through quantitative reverse transcription-polymerase chain reaction. The results of this study will help facilitate exploration of the development and maintenance of the phenotypic sex mechanism in P. olivaceus.

Molecular cloning and sexually dimorphic expression of wnt4 in olive flounder (Paralichthys olivaceus)

WNT4 (wingless-type MMTV integration site family, member 4) is regarded as a key regulator of gonad differentiation in mammalians. However, the potential role of wnt4 in teleosts during gonad differentiation and development is still unclear. The full-length cDNA sequence of wnt4 in olive flounder (Paralichthys olivaceus) was obtained using RACE (rapid amplification of cDNA ends) technique. The wnt4 ORF contains 1059 nucleotides, encoding a protein with a signal peptide domain and a wnt family domain. Expression in tissues of adult flounders was analyzed by real-time RT-PCR. The results showed that wnt4 was widely expressed in multiple tissues of flounders, and the expression level was significantly higher in ovary than in testis. Then wnt4 expression pattern was investigated during gonadal differentiation period and at gonadal development stages (I-V). The results showed the expression levels were significantly higher in testis than in ovary during gonadal differentiation. Notably, wnt4 expression had a very significant increase before testis differentiation. At gonad different developmental stages, there was no expression signal at stage I or stage II, and the expression of wnt4 was much stronger in ovary than in testis at stage III and stage IV, followed by a faint expression in stage V in both sexes. Our results imply that cloned wnt4 could be wnt4a. It is a sex-related gene and its expression pattern in gonadal differentiation period of flounder is different from that in mammalians or other teleosts. Flounder wnt4 might play more important role in testis than in ovary during gonadal differentiation.

A Novel Female-Specific and Sexual Reproduction-Associated Dmrt Gene Discovered in the Stony Coral, Euphyllia ancora

Transcription factors encoded by the Dmrt gene family regulate multiple aspects of animal reproduction. Most studies investigating the Dmrt gene family were conducted in model organisms from bilateral species, with a particular emphasis on gene function in male sex determination. It is still unclear whether the E. ancora Dmrt (EaDmrt) genes found in basal metazoans such as cnidarians share similar characteristics with orthologs in other metazoans. In this study, seven full Dmrt gene transcript sequences for a gonochoric coral, Euphyllia ancora (phylum: Cnidaria; class: Anthozoa), were obtained through transcriptome data mining, RT-PCR analysis, rapid amplification of cDNA ends, and sequencing. These EaDmrts were subjected to quantitative assays measuring temporal and tissue-specific expression. Results demonstrated a unique gene expression pattern for EaDmrtE, which is enriched in female germ cells during the spawning season. Based on the phylogenetic analyses performed across the homologous Dmrt genes in metazoans, we found that the female-specific EaDmrtE gene is not related to the DM1 gene of Acropora spp. coral nor to Dmrt1 of vertebrates, which are involved in sexual reproduction, especially in sex determination (vertebrate Dmrt1). Additionally, high levels of EaDmrtE transcripts detected in unfertilized mature eggs are retained in newly formed zygotes but decrease during embryonic development. We suggest that the newly discovered gene may play a role in oogenesis and early embryogenesis as a maternal factor in corals. Therefore, the sexual reproduction-associated Dmrt gene(s) should have arisen in cnidarians and might have evolved multiple times in metazoans.

Sexually dimorphic gene expression patterns during gonadal differentiation in olive flounder, Paralichthys olivaceus

The present study aims to elucidate the different expression patterns and possible roles of Doublesex and Mab-3-related transcription factor 1 (dmrt1), dmrt4, SRY-related transcription factor 9 (sox9) and cytochrome P450 aromatase 19a (cyp19a) during gonadal differentiation in olive flounder, Paralichthys olivaceus. We first analyzed the gene expression patterns in tissues using RT-PCR, which indicated dmrt1, sox9 and cyp19a were sex-related genes with sexual dimorphic expression. The quantitative expression changes of these three genes together with dmrt4 during gonadal differentiation were further examined using real-time RT-PCR. The results showed that dmrt1 was scarcely expressed in the primitive gonad and during following periods of gonadal differentiation. Its expression increased rapidly in the differentiating testis. Dmrt4 was strongly expressed in primitive gonads and much less expressed during following periods of gonadal differentiation. Its expression became strong in differentiating testes. While sox9 was highly expressed in the primitive gonad, it was expressed with fluctuations during following periods of gonadal differentiation. Cyp19a started expressing in primitive gonads, and its expression quantity fluctuated during latter periods of gonadal differentiation, but was strongly expressed in the early stage of differentiating ovaries. Results of in situ hybridization showed that dmrt4 and sox9 transcripts were both mainly localized in spermatocytes and our results suggested these four sex-related genes might be involved in gonadal differentiation through their synergistic effects in flounder.

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 1,587 bp 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 35 days 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.

Gonadal transcriptome analysis of male and female olive flounder (Paralichthys olivaceus)

Olive flounder (Paralichthys olivaceus) is an important commercially cultured marine flatfish in China, Korea, and Japan, of which female grows faster than male. In order to explore the molecular mechanism of flounder sex determination and development, we used RNA-seq technology to investigate transcriptomes of flounder gonads. This produced 22,253,217 and 19,777,841 qualified reads from ovary and testes, which were jointly assembled into 97,233 contigs. Among them, 23,223 contigs were mapped to known genes, of which 2,193 were predicted to be differentially expressed in ovary and 887 in testes. According to annotation information, several sex-related biological pathways including ovarian steroidogenesis and estrogen signaling pathways were firstly found in flounder. The dimorphic expression of overall sex-related genes provides further insights into sex determination and gonadal development. Our study also provides an archive for further studies of molecular mechanism of fish sex determination.

CpG methylation of dmrt1 and cyp19a promoters in relation to their sexual dimorphic expression in the Japanese flounder Paralichthys olivaceus

To better understand the effects of DNA methylation on the expression patterns of dmrt1 (Doublesex and Mab-3-related transcription factor 1) and cyp19a (Cytochrome P450 19a) in the Japanese flounder Paralichthys olivaceus, quantitative expressions, cellular distributions and cytosine-p-guanine (CpG) methylation patterns of these two genes in the gonads were analysed. The results showed that P. olivaceus dmrt1 expression was 70 times higher in the testis than in the ovary (P < 0·05). Its mRNA was detected clearly in spermatocytes and Sertoli cells of the testis, but weakly in the ovary. Paralichthys olivaceus cyp19a expression was 40 times higher in the ovary than in the testis (P < 0·01). Its mRNA was detected clearly in follicular cells of the ovary, but weakly in spermatocytes of the testis. The dmrt1 promoter CpGs were not methylated in the testis, whereas 57·69% were methylated in the ovary. For the cyp19a promoter CpGs, 97·5% were methylated in the testis and 73·33% were methylated in the ovary. These findings demonstrate that P. olivaceus dmrt1 and cyp19a are sex-related genes with sexual dimorphic expression, CpG methylation levels of the two genes are consistent with their expression quantities, and this epigenetic modification can influence the differential expression of genes in the gonads of P. olivaceus.

FGF signaling establishes the anterior border of the Ciona neural tube

The Ciona tadpole is constructed from simple, well-defined cell lineages governed by provisional gene networks that have been defined via extensive gene disruption assays. Here, we examine the patterning of the anterior neural plate, which produces placodal derivatives such as the adhesive palps and stomodeum, as well as the sensory vesicle (simple brain) of the Ciona tadpole. Evidence is presented that the doublesex-related gene DMRT is expressed throughout the anterior neural plate of neurulating embryos. It leads to the activation of FoxC and ZicL in the palp placode and anterior neural tube, respectively. This differential expression depends on FGF signaling, which inhibits FoxC expression in the anterior neural tube. Inhibition of FGF signaling leads to expanded expression of FoxC, the loss of ZicL, and truncation of the anterior neural tube.

Dmrt1 genes at the crossroads: a widespread and central class of sexual development factors in fish

A plethora of corroborative genetic studies led to the view that, across the animal kingdom, the gene-regulatory cascades triggering sexual development bear little resemblance to each other. As a result, the common emerging picture is that the genes at the top of the cascade are not conserved, whereas the downstream genes have homologues in a much broader spectrum of species. Among these downstream effectors, a gene family involved in sex differentiation in organisms as phylogenetically divergent as corals, Caenorhabditis elegans, Drosophila, frogs, fish, birds and mammals is the dmrt gene family. Despite the attention that Dmrt1 factors have received, to date it has not been elucidated how Dmrt1s mediate their activities and putative downstream targets have yet to be characterized. However, a remarkable amount of descriptive expression data has been gathered in a large variety of fish, particularly with respect to early gonadal differentiation and sex change. This minireview aims at distilling the current knowledge of fish dmrt1s, in terms of expression and regulation. It is shown how gonadal identities correlate with dimorphic dmrt1 expression in gonochoristic and hermaphroditic fish species. It is also described how sex steroid hormones affect gonadal identity and dmrt1 expression. Emphasis is also given to recent findings dealing with transcriptional, post-transcriptional, post-translational and functional regulations of the dmrt1a/dmrt1bY gene pair in medaka.