Maternal inheritance of Nanog ortholog in blunt-snout bream

Medaka (Oryzias latipes) Dmrt3a Is Involved in Male Fertility

Research across various species has demonstrated that the doublesex and mab-3-related transcription factor 3 (dmrt3) plays pivotal roles in testis development. However, the precise molecular mechanisms of dmrt3 remain unclear. In this study, we investigated the role of dmrt3 (dmrt3a) in testis development using the model organism medaka (Oryzias latipes). SqRT-PCR and ISH analyses revealed that dmrt3a is predominantly expressed in the testis, especially in the spermatid and spermatozoon. Using CRISPR/Cas9, we generated two dmrt3a homozygous mutants (-8 bp and -11 bp), which exhibited significantly reduced fertilization rates and embryo production. Additionally, the number of germ cells and sperm motility were markedly decreased in the dmrt3a mutants, manifesting as the symptoms of asthenozoospermia and oligozoospermia. Interestingly, RNA-Seq analysis showed that the deficiency of dmrt3a could lead to a significant downregulation of numerous genes related to gonadal development and severe disruptions in mitochondrial function. These results suggested that dmrt3a is essential for spermatogenesis and spermatozoa energy production. This paper provides new insights and perspectives for further exploring the molecular mechanisms underlying spermatogenesis and addressing male reproductive issues.

Characteristics of the Vasa Gene in Silurus asotus and Its Expression Response to Letrozole Treatment

The identification and expression of germ cells are important for studying sex-related mechanisms in fish. The vasa gene, encoding an ATP-dependent RNA helicase, is recognized as a molecular marker of germ cells and plays a crucial role in germ cell development. Silurus asotus, an important freshwater economic fish species in China, shows significant sex dimorphism with the female growing faster than the male. However, the molecular mechanisms underlying these sex differences especially involving in the vasa gene in this fish remain poorly understood. In this work, the vasa gene sequence of S. asotus (named as Savasa) was obtained through RT-PCR and rapid amplification of cDNA end (RACE), and its expression in embryos and tissues was analyzed using qRT-PCR and an in situ hybridization method. Letrozole (LT) treatment on the larvae fish was also conducted to investigate its influence on the gene. The results revealed that the open reading frame (ORF) of Savasa was 1989 bp, encoding 662 amino acids. The SaVasa protein contains 10 conserved domains unique to the DEAD-box protein family, showing the highest sequence identity of 95.92% with that of Silurus meridionalis. In embryos, Savasa is highly expressed from the two-cell stage to the blastula stage in early embryos, with a gradually decreasing trend from the gastrula stage to the heart-beating stage. Furthermore, Savasa was initially detected at the end of the cleavage furrow during the two-cell stage, later condensing into four symmetrical cell clusters with embryonic development. At the gastrula stage, Savasa-positive cells increased and began to migrate towards the dorsal side of the embryo. In tissues, Savasa is predominantly expressed in the ovaries, with almost no or lower expression in other detected tissues. Moreover, Savasa was expressed in phase I-V oocytes in the ovaries, as well as in spermatogonia and spermatocytes in the testis, implying a specific expression pattern of germ cells. In addition, LT significantly upregulated the expression of Savasa in a concentration-dependent manner during the key gonadal differentiation period of the fish. Notably, at 120 dph after LT treatment, Savasa expression was the lowest in the testis and ovary of the high concentration group. Collectively, findings from gene structure, protein sequence, phylogenetic analysis, RNA expression patterns, and response to LT suggest that Savasa is maternally inherited with conserved features, serving as a potential marker gene for germ cells in S.asotus, and might participate in LT-induced early embryonic development and gonadal development processes of the fish. This would provide a basis for further research on the application of germ cell markers and the molecular mechanisms of sex differences in S. asotus.

The Divergent and Conserved Expression Profile of Turtle Nanog Gene Comparing with Fish and Mammals

Nanog is a homeodomain-containing transcription factor, and it plays a vital role in maintaining the pluripotency of embryonic stem cells. Nanog’s function has been well studied in many species. However, there is lack of reporting on the Nanog gene in reptile. Here, we identified a 1032 bp cDNA sequence of a Nanog gene in Pelidiscus sinensis, known as PsNanog. PsNanog has a highly conserved HD domain and shares a high identity with that of Chelonia mydas and the lowest identity with Oryzias latipes. Similarly, PsNanog presented a tight cluster with C. mydas Nanog, but was far from those of teleosts. Additionally, we cloned a length of 1870 bp PsNanog promoter. Dual luciferase assay showed that the DNA fragment of −1560 to +1 exhibited a high promoter activity. The RT-PCR and RT-qPCR results showed that PsNanog was predominantly expressed in ovary, and then in testis. The in situ hybridization and immunohistochemical analysis showed that PsNanog was expressed in the early primary oocytes and the cytoplasm of the cortical region of stage VIII oocytes in ovary, and distributed in most stages of germ cells in testis. Collectively, the results imply that PsNanog probably has the conserved function in regulating germ cell development across phyla and is also a pluripotent cell gene and expressed in germ cells, which is similar to that in teleosts and mammals.

Characterization of the Nanog gene involved in the gonadal development in pearlscale angelfish (Centropyge vrolikii)

The homeodomain transcription factor Nanog plays a crucial role in the embryonic and gonadal development and the maintenance of embryonic stem cells (ESCs), interacting with transcription factors such as Oct4 and Sox2 in mammals. Nevertheless, its pathways to molecular mechanisms remain unclear as to teleosts. This study investigates the role of the Nanog gene in gonadal development and sex reversal of pearlscale angelfish (Centropyge vrolikii). To understand the expression pattern of gonadal development, we identified the Nanog gene of C. vrolikii, which we named Cv-Nanog. The full-length cDNA sequence of Cv-Nanog was 2,136 bp in length and encoded a homeodomain protein of 436 amino acid residues. The gene structure and western blot prove results that Cv-Nanog was homologous to the Nanog gene of mammalians. The protein sequence comparison demonstrates that the Cv-Nanog shared a high degree of similarity with orthologs from other vertebrates in the conserved homeodomain. The Cv-Nanog gene was substantially expressed in gonads, and the expression was significantly higher in the ovaries than in the testis, according to quantitative real-time PCR (qRT-PCR) and western blot analyses. In situ hybridization reveals that the transcripts were located in the cytoplasm and membrane of the oocytes in the ovaries and testes. The expression of Cv-Nanog mRNA was weak in Sertoli cells but strong in germ cells. After overexpression of Cv-Nanog, the expression levels of pluripotent factors Sox2 and Oct4 increased significantly with 21.5-fold and 12.2-fold, respectively. Simultaneously, the TGF-beta signaling pathway was activated, and the gonadal cell growth was promoted. The expression of ovary-bias genes Cyp19a and Foxl2 was upregulated, and the expression of testis-bias genes Sox9 and Dmrt1 was downregulated to promote ovarian development. These results imply that the Nanog gene might play a crucial role in the process of gonadal development and sexual reversion in C. vrolikii. This study provides new insight to understand the molecular regulatory mechanism of the Nanog gene further and important clues for the future studies in gonadal development.

Characterization of nanog in Nile tilapia (Oreochromis niloticus) and its spatiotemporal expression patterns during embryonic and gonadal development

Nanog is one of the well-characterized core transcription factors in pluripotency maintenance network. So far, studies on fishes indicate that the Nanog expression occurs from embryonic 1-cell stage to blastula stage, and is restricted to the gonadal germline cells in adult tissues, which is strikingly different from that in mammals. However, whether this expression profile is conservative in fishes remains to be investigated. Here Nile tilapia (Oreochromis niloticus) nanog (named as Ong) was identified and its spatiotemporal expression patterns during embryonic and gonadal development were investigated. The Ong cDNA contains an open reading frame of 678 bp, encoding 226 amino acids. The anti-Ong antibody was prepared through prokaryotic protein expression and its specificity was validated. The Ong expression in embryonic 1-cell stage did not appear until the early stage of blastocyst and continued to the late stage of blastocyst. In adult tissues, its expression was limited to gonads. Its expression patterns during gonadal development were further investigated by in situ hybridization and immunohistochemical staining. In testis, Ong was not expressed at 30 dah (days after hatching), but highly expressed in spermatogonia and spermatocytes at 150 dah; in ovaries at 30 and 150 dah, it was not expressed in germline cells but in all somatic cells. This expression profile is strikingly different from reports in fishes to date. Our study firstly indicates that the Nanog expression profile is not conservative in fishes. This study is valuable for further functional and evolutionary study of this gene.

Pou5f1 and Nanog Are Reliable Germ Cell-Specific Genes in Gonad of a Protogynous Hermaphroditic Fish, Orange-Spotted Grouper (Epinephelus coioides)

Pluripotency markers Pou5f1 and Nanog are core transcription factors regulating early embryonic development and maintaining the pluripotency and self-renewal of stem cells. Pou5f1 and Nanog also play important roles in germ cell development and gametogenesis. In this study, Pou5f1 (EcPou5f1) and Nanog (EcNanog) were cloned from orange-spotted grouper, Epinephelus coioides. The full-length cDNAs of EcPou5f1 and EcNanog were 2790 and 1820 bp, and encoded 475 and 432 amino acids, respectively. EcPou5f1 exhibited a specific expression in gonads, whereas EcNanog was expressed highly in gonads and weakly in some somatic tissues. In situ hybridization analyses showed that the mRNA signals of EcNanog and EcPou5f1 were exclusively restricted to germ cells in gonads. Likewise, immunohistofluorescence staining revealed that EcNanog protein was limited to germ cells. Moreover, both EcPou5f1 and EcNanog mRNAs were discovered to be co-localized with Vasa mRNA, a well-known germ cell maker, in male and female germ cells. These results implied that EcPou5f1 and EcNanog could be also regarded as reliable germ cell marker genes. Therefore, the findings of this study would pave the way for elucidating the mechanism whereby EcPou5f1 and EcNanog regulate germ cell development and gametogenesis in grouper fish, and even in other protogynous hermaphroditic species.

Gonadal, Not Maternal, Acquisition of Duplicated pax6 Orthologs in Megalobrama Amblycephala

: The highly conserved transcription factor Pax6 is involved in the development of the eyes, brain, and pancreas in vertebrates and invertebrates, whereas the additional expression pattern in other organs is still elusive. In this study, we cloned and characterized two pax6 homologs in blunt snout bream (Megalobrama amblycephala), named Mapax6a and Mapax6b. The protein alignment and phylogenetic tree showed that Mapax6a and Mapax6b were highly conserved compared with their counterparts in other species. Genomic information analysis revealed that the synteny conservation of Wilms tumor, Aniridia, genitourinary abnormalities, and mental retardation loci was also maintained in this species. By reverse transcription polymerase chain reaction, the expression of Mapax6a was later than that of Mapax6b which was found in the blastula stage, while the expression of Mapax6a started from the somite stage, and both of them persisted in a subsequent stage during the embryonic development. By RNA and protein detection, Mapax6a and Mapax6b were detected in the eye and brain as canonic patterns, and most importantly, they were also enriched in germ cells of the testis and ovary. Therefore, our findings validate the duplication of pax6 in fish, confirm the classical expression patterns in the brain and eye, and, for the first time, present a new acquisition of Mapax6a and Mapax6b in gonadal germ cells in particular. Therefore, our results enrich the expression pattern and evolutionary relationship of pax6 by suggesting that duplicated Mapax6 is involved in gametogenesis in Megalobrama amblycephala.