pSTAT3 activation of Foxl2 initiates the female pathway underlying temperature-dependent sex determination.

Ovarian development was traditionally recognized as a "default" sexual outcome and therefore received much less scientific attention than testis development. In turtles with temperature-dependent sex determination (TSD), how the female pathway is initiated to induce ovary development remains unknown. In this study, we have found that phosphorylation of the signal transducer and activator of transcription 3 (pSTAT3) and Foxl2 exhibit temperature-dependent sexually dimorphic patterns and tempo-spatial coexpression in early embryos of the red-eared slider turtle (Trachemys scripta elegans). Inhibition of pSTAT3 at a female-producing temperature of 31 °C induces 64.7% female-to-male sex reversal, whereas activation of pSTAT3 at a male-producing temperature of 26 °C triggers 75.6% male-to-female sex reversal. In addition, pSTAT3 directly binds to the locus of the female sex-determining gene Foxl2 and promotes Foxl2 transcription. Overexpression or knockdown of Foxl2 can rescue the sex reversal induced by inhibition or activation of pSTAT3. This study has established a direct genetic link between warm temperature-induced STAT3 phosphorylation and female pathway initiation in a TSD system, highlighting the critical role of pSTAT3 in the cross talk between female and male pathways.

Overexpression of Kdm6b induces testicular differentiation in a temperature-dependent sex determination system.

In reptiles, such as the red-eared slider turtle ( Trachemys scripta elegans), gonadal sex determination is highly dependent on the environmental temperature during embryonic stages. This complex process, which leads to differentiation into either testes or ovaries, is governed by the finely tuned expression of upstream genes, notably the testis-promoting gene Dmrt1 and the ovary-promoting gene Foxl2. Recent studies have identified epigenetic regulation as a crucial factor in testis development, with the H3K27me3 demethylase KDM6B being essential for Dmrt1 expression in T. s. elegans. However, whether KDM6B alone can induce testicular differentiation remains unclear. In this study, we found that overexpression of Kdm6b in T. s. elegans embryos induced the male development pathway, accompanied by a rapid increase in the gonadal expression of Dmrt1 at 31°C, a temperature typically resulting in female development. Notably, this sex reversal could be entirely rescued by Dmrt1 knockdown. These findings demonstrate that Kdm6b is sufficient for commitment to the male pathway, underscoring its role as a critical epigenetic regulator in the sex determination of the red-eared slider turtle.

[Estrogen receptor Esr1 induces early ovarian differentiation in Trachemys scripta].

This study aims to explore the roles of three estrogen receptors (Esr1, Esr2, and Gper1) in early differentiation of embryonic gonads of Trachemys scripta. The expression characteristics of the receptor genes were studied first. The Esr1, Esr2, and Gper1 agonists PPT, WAY 200070, and G-1 were respectively injected into the embryos at the male-producing temperature (MPT) before initiation of gonadal differentiation. The sex reversal of the treated embryonic gonads was analyzed in terms of morphological structure of gonads, distribution pattern of germ cells, and expression of key genes and proteins involved in sex differentiation. The expression level of esr1 during the critical stage of sex differentiation was higher than those of esr2 and gper1 (very low expression) and was particularly high in the gonads at the female-producing temperature (FPT). After treatment with PPT, the MPT gonads presented obviously feminized morphology and structure, with the germ cells exhibiting a female distribution pattern. Furthermore, the mRNA expression levels of the key genes (dmrt1, amh, and sox9) for male differentiation were down-regulated significantly, while those of the key genes (foxl2 and cyp19a1) for female differentiation were up-regulated observably. The fluorescent signals of Amh and Sox9 expression almost disappeared, while Foxl2 and Arom were activated to express abundantly, which fully demonstrated the sex reversal of the gonads from male to female (sex reversal rate: 70.27%). However, the MPT gonads treated with WAY 200070 and G-1 still differentiated into testes, and the expression patterns of the key genes and proteins were similar to those in male gonads. The above results demonstrate that activation of Esr1 alone can fully initiate the early female differentiation process of gonads, suggesting that estrogen may induce early ovarian differentiation via Esr1 in Trachemys scripta. The findings provide a basis for further revealing the mechanisms of estrogen regulation in sex determination and differentiation of turtles.

Insights into sequence characteristics and evolutionary history of DGATs in arthropods.

Triacylglycerol (TAG) is crucial in animal energy storage and membrane biogenesis. The conversion of diacylglycerol (DAG) to triacylglycerol (TAG) is catalyzed by diacylglycerol acyltransferase enzymes (DGATs), which are encoded by genes belonging to two distinct gene families. Although arthropods are known to possess DGATs activities and utilize the glycerol-3-phosphate pathway and MAG pathway for TAG biosynthesis, the sequence characterization and evolutionary history of DGATs in arthropods remains unclear. This study aimed to comparatively evaluate genomic analyses of DGATs in 13 arthropod species and 14 outgroup species. We found that arthropods lack SOAT2 genes within the DGAT1 family, while DGAT2, MOGAT3, AWAT1, and AWAT2 were absent from in DGAT2 family. Gene structure and phylogenetic analyses revealed that DGAT1 and DGAT2 genes come from different gene families. The expression patterns of these genes were further analyzed in crustaceans, demonstrating the importance of DGAT1 in TAG biosynthesis. Additionally, we identified the DGAT1 gene in Swimming crab (P. trituberculatus) undergoes a mutually exclusive alternative splicing event in the molt stages. Our newly determined DGAT inventory data provide a more complete scenario and insights into the evolutionary dynamics and functional diversification of DGATs in arthropods.

MicroRNA transcriptome analysis for elucidating the immune mechanism of the redclaw crayfish Cherax quadricarinatus under Decapod iridescent virus 1 infection.

Redclaw crayfish (Cherax quadricarinatus) is a large, tropical freshwater crustacean species with considerable potential of commercial production. In recent years, infection with DIV1 in redclaw crayfish is being reported in aquaculture industries, causing high mortality and huge economic losses. However, many characteristics of this virus, including pathogenesis, transmission mechanism, and host immunity, remain largely unknown.MicroRNAs are known to play important roles in numerous biological processes, and many microRNAs are reported to be involved in the regulation of immune responses. In this study, nine-small RNA libraries were constructed using hemocytes of redclaw crayfish to characterize the differentially expressed miRNAs (DE-miRNAs) at 24 and 48 h postinfection (hpi). A total of 14 and 22 DE-miRNAs were identified in response to DIV1 infection at 24 and 48 hpi, respectively. Further, functional annotation of the predicted host target genes using GO and KEGG pathway enrichment analyses indicated that relevant biological processes and signal pathways underwent miRNA-mediated regulation after DIV1 infection. Our results enhanced the understanding of the mechanisms of miRNA-mediated regulation of immune responses under DIV1 infection in crustaceans.

Evidence for RA-dependent meiosis onset in a turtle embryo.

Meiotic entry is one of the earliest sex determination events of the germ cell in higher vertebrates. Although advances in meiosis onset have been achieved in mammals, birds and fish, how this process functions in reptiles is largely unknown. In this study, we present the molecular analysis of meiosis onset and the role of retinoic acid (RA) in this process in the red-eared slider turtle. Our results using Stra8 as a pre-meiosis indicator show that in the female embryonic gonad, meiosis commitment starts around stage 19. Additionally, signals of the meiosis marker Sycp3 could be detected at stage 19 and become highly expressed by stage 23. No expression of these genes was detected in male embryonic gonads, suggesting the entry into meiosis prophase I was restricted to female embryonic germ cells. Notably, RA activity in fetal gonads is likely to be elevated in females than that in males, as evidenced by the higher expression of RA synthase Aldh1a1 and lower expression of RA-degrading enzyme Cyp26a1 in female gonads prior to meiotic entry. In addition, exogenous RA treatment induced the expression of Stra8 and Sycp3 in both sexes, whether in vivo or in vitro. Together, these results indicate that high levels of RA in the embryonic female gonads can lead to the initiation of meiosis in the turtle.

SOX8 is essential for male sexual differentiation in the Chinese soft-shelled turtle Pelodiscus sinensis‡.

SOX8, which belongs to SOXE transcription factor subfamily together with SOX9, participates in sex differentiation and testicular development by enhancing the function of SOX9 in mammals. However, the functional role of SOX8 in sex differentiation has not yet been identified in any non-mammalian vertebrates. Here, we found in the Chinese soft-shelled turtle Pelodiscus sinensis that SOX8 exhibited male-specific higher expression from stage 14 to 18, the critical period of sex determination, prior to the onset of gonadal differentiation. In addition, SOX8 was rapidly down-regulated during male-to-female sex reversal induced by estradiol. Moreover, knockdown of SOX8 led to complete feminization of ZZ P. sinensis, determined by gonadal morphology and distribution of germ cells, as well as the down-regulation of testicular marker DMRT1 and the up-regulation of ovarian regulator FOXL2. In conclusion, this study provides evidence that SOX8 is a key regulator of early male differentiation in P. sinensis, highlighting the significance of the SOX family in reptile sex determination.

Loss- and gain-of-function analyses reveal the essential role of Cyp19a1 in ovarian determination of the red-eared slider turtle.

Estrogen signaling exerts a decisive role in female sex determination and differentiation in chicken and fish. Aromatase encoded by Cyp19a1 is the key enzyme that catalyzes the conversion of androgen to estrogen. Correlative analyses implicate the potential involvement of aromatase in reptilian sexual development, however, the direct genetic evidence is lacking. Herein, we found that Cyp19a1 exhibited temperature-dependent sexually dimorphic expression, and located in the medullary somatic cells in early female embryos of the red-eared slider turtle (Trachemys scripta elegans), before the gonad is distinct. To determine the functional role of Cyp19a1 in turtle ovarian determination, we established loss- and gain-of-function models through in ovo lentivirus-mediated genetic manipulation. At female-producing temperature, inhibition of aromatase or knockdown of Cyp19a1 in turtle embryos resulted in female-to-male sex reversal, with the formation of a testis-like structure and a male distribution pattern of germ cells, as well as ectopic expression of male-specific markers (SOX9 and AMH) and disappearance of ovarian regulator FOXL2. On the contrary, overexpression of Cyp19a1 at male-producing temperature led to male-to-female sex reversal. In conclusion, our results suggest that Cyp19a1 is both necessary and sufficient for ovarian determination in the red-eared slider turtle, establishing causality and a direct genetic link between aromatase and reptilian sex determination and differentiation.

The forkhead factor Foxl2 participates in the ovarian differentiation of Chinese soft-shelled turtle Pelodiscus sinensis.

The forkhead transcription factor Foxl2 plays a major role in ovarian development and function in mice and fish, and acts as a female sex-determining gene in goat. Its functional role in the sex determination and gonadal differentiation has not yet been investigated in reptiles. Here, we characterized Foxl2 gene in Chinese soft-shelled turtle Pelodiscus sinensis, exhibiting ZZ/ZW sex chromosomes. Foxl2 exhibited a female-specific embryonic expression pattern throughout the critical sex determination periods in P. sinensis. The expression of Foxl2 was induced at early stage in ZZ embryonic gonads that were feminized by estrogen treatment. Most importantly, Foxl2 knockdown in ZW embryos by RNA interference resulted in female-to-male sex reversal, characterized by obvious masculinization of gonads, significant up-regulation of testicular markers Dmrt1 and Sox9, and remarkable down-regulation of ovarian regulator Cyp19a1. Conversely, gain-of-function study showed that overexpression of Foxl2 in ZZ embryos led to largely feminized genetic males, production of Cyp19a1, and a decline in Dmrt1 and Sox9. These findings demonstrate that Foxl2 is both necessary and sufficient to initiate ovarian differentiation in P. sinensis, thereby acting as a key upstream regulator of the female pathway in a reptilian species.

Foxl2 is required for the initiation of the female pathway in a temperature-dependent sex determination system in Trachemys scripta.

KDM6B-mediated epigenetic modification of the testicular regulator Dmrt1 has previously been identified as the primary switch of the male pathway in a temperature-dependent sex-determination (TSD) system; however, the molecular network of the female pathway has not yet been established. Here, we have functionally characterized for the first time an upstream regulator of the female pathway, the forkhead transcription factor FOXL2, in Trachemys scripta, a turtle species with a TSD system. FOXL2 exhibited temperature-dependent female-specific expression patterns before the onset of gonadal differentiation and was preferentially localized in ovarian somatic cells. Foxl2 responded rapidly to temperature shifts and estrogen. Importantly, forced expression of Foxl2 at the male-producing temperature led to male-to-female sex reversal, as evidenced by the formation of an ovary-like structure, and upregulation of the ovarian regulators Cyp19a1 and R-spondin1. Additionally, knockdown of Foxl2 caused masculinization at the female-producing temperature, which was confirmed by loss of the female phenotype, development of seminiferous tubules, and elevated expression of Dmrt1 and Sox9. Collectively, we demonstrate that Foxl2 expression is necessary and sufficient to drive ovarian determination in T. scripta, suggesting a crucial role of Foxl2 in female sex determination in the TSD system.

Sex determination mechanisms and sex control approaches in aquaculture animals.

Aquaculture is one of the most efficient modes of animal protein production and plays an important role in global food security. Aquaculture animals exhibit extraordinarily diverse sexual phenotypes and underlying mechanisms, providing an ideal system to perform sex determination research, one of the important areas in life science. Moreover, sex is also one of the most valuable traits because sexual dimorphism in growth, size, and other economic characteristics commonly exist in aquaculture animals. Here, we synthesize current knowledge of sex determination mechanisms, sex chromosome evolution, reproduction strategies, and sexual dimorphism, and also review several approaches for sex control in aquaculture animals, including artificial gynogenesis, application of sex-specific or sex chromosome-linked markers, artificial sex reversal, as well as gene editing. We anticipate that better understanding of sex determination mechanisms and innovation of sex control approaches will facilitate sustainable development of aquaculture.

ESR1 mediates estrogen-induced feminization of genetic male Chinese soft-shelled turtle†.

Exogenous estrogen have shown their feminization abilities during the specific sex differentiation period in several reptiles. However, the specific regulatory mechanism and downstream regulatory genes of estrogen remain elusive. In the present study, 17ß-estradiol (E2), as well as drugs of specific antagonists and/or agonists of estrogen receptors, were employed to figure out the molecular pathway involved in the E2-induced feminization in Chinese soft-shelled turtles, an important aquaculture species in China. E2 treatment led to typical female characteristics in the gonads of ZZ individuals, including thickened outer cortex containing a number of germ cells and degenerated medullary cords, as well as the disappearance of male marker SOX9, and the ectopic expression of ovarian regulator FOXL2 at the embryonic developmental stage 27 and 1 month after hatching. The specific ESR1 antagonist or a combination of three estrogen receptor antagonists could block the sex reversal of ZZ individuals induced by estrogen. In addition, specific activation of ESR1 by agonist also led to the feminization of ZZ gonads, which was similar to the effect of estrogen treatment. Furthermore, transcriptome data showed that the expression level of FOXL2 was significantly upregulated, whereas mRNA levels of DMRT1, SOX9, and AMH were downregulated after estrogen treatment. Taken together, our results indicated that E2 induced the feminization of ZZ Chinese soft-shelled turtles via ESR1, and decrease of male genes DMRT1, SOX9, and AMH and increase of ovarian development regulator FOXL2 might be responsible for the initiation of E2-induced feminization.

Knockdown of R-spondin1 leads to partial sex reversal in genetic female Chinese soft-shelled turtle Pelodiscus sinensis.

Chinese soft-shelled turtle Pelodiscus sinensis is an important aquaculture species in China, the male individual being more valuable in aquaculture because of its larger body size, higher growth rate and less fat compared with females. Understanding the mechanism of ovarian differentiation and development is crucial for the production of mono-sex male offspring. However, little is known about the molecular mechanism underlying turtle ovarian differentiation. Here, we characterized the Rspo1 gene, an upstream regulator of vertebrate female sexual differentiation, in P. sinensis. The messenger RNA of Rspo1 was initially expressed at stage 14, preceding gonadal sex differentiation, and exhibited a sexually dimorphic expression pattern throughout the sex determination and gonadal differentiation periods. Rspo1 was rapidly downregulated during aromatase inhibitor-induced female-to-male sex reversal, which occurred prior to gonadal differentiation. Rspo1 loss of function by RNA interference led to partial female-to-male sex reversal, with masculinized changes in the phenotype of gonads, the distribution of germ cells and the expression of testicular regulators. Collectively, these findings suggest that Rspo1 is necessary for primary female sexual differentiation in P. sinensis. This study demonstrates for the first time the functional role of Rspo1 in reptilian sex determination, and is of fundamental significance for the production of fertile pseudo-female parents and mono-sex male offspring of P.sinensis.

Temperature-dependent sex determination is mediated by pSTAT3 repression of Kdm6b.

In many reptiles, including the red-eared slider turtle Trachemys scripta elegans (T. scripta), sex is determined by ambient temperature during embryogenesis. We previously showed that the epigenetic regulator Kdm6b is elevated at the male-producing temperature and essential to activate the male pathway. In this work, we established a causal link between temperature and transcriptional regulation of Kdm6b We show that signal transducer and activator of transcription 3 (STAT3) is phosphorylated at the warmer, female-producing temperature, binds the Kdm6b locus, and represses Kdm6b transcription, blocking the male pathway. Influx of Ca2+, a mediator of STAT3 phosphorylation, is elevated at the female temperature and acts as a temperature-sensitive regulator of STAT3 activation.

The Role of Anti-Müllerian Hormone in Testis Differentiation Reveals the Significance of the TGF-ß Pathway in Reptilian Sex Determination.

Anti-Müllerian hormone (Amh, or Müllerian-inhibiting substance, Mis), a member of TGF-ß superfamily, has been well documented in some vertebrates as initiator or key regulator in sexual development, and particularly in fish. However, its functional role has not yet been identified in reptiles. Here, we characterized the Amh gene in the Chinese soft-shelled turtle Pelodiscus sinensis, a typical reptilian species exhibiting ZZ/ZW sex chromosomes. The messenger RNA of Amh was initially expressed in male embryonic gonads by stage 15, preceding gonadal sex differentiation, and exhibited a male-specific expression pattern throughout embryogenesis. Moreover, Amh was rapidly upregulated during female-to-male sex reversal induced by aromatase inhibitor letrozole. Most importantly, Amh loss of function by RNA interference led to complete feminization of genetic male (ZZ) gonads, suppression of the testicular marker Sox9, and upregulation of the ovarian regulator Cyp19a1 Conversely, overexpression of Amh in ZW embryos resulted in female-to-male sex reversal, characterized by the formation of a testis structure, ectopic activation of Sox9, and a remarkable decline in Cyp19a1 Collectively, these findings provide the first solid evidence that Amh is both necessary and sufficient to drive testicular development in a reptilian species, P. sinensis, highlighting the significance of the TGF-ß pathway in reptilian sex determination.

The histone demethylase KDM6B regulates temperature-dependent sex determination in a turtle species.

Temperature-dependent sex determination is a notable model of phenotypic plasticity. In many reptiles, including the red-eared slider turtle Trachemys scripta elegans (T. scripta), the individual's sex is determined by the ambient temperature during egg incubation. In this study, we show that the histone H3 lysine 27 (H3K27) demethylase KDM6B exhibits temperature-dependent sexually dimorphic expression in early T. scripta embryos before the gonad is distinct. Knockdown of Kdm6b at 26°C (a temperature at which all offspring develop into males) triggers male-to-female sex reversal in >80% of surviving embryos. KDM6B directly promotes the transcription of the male sex-determining gene Dmrt1 by eliminating the trimethylation of H3K27 near its promoter. Additionally, overexpression of Dmrt1 is sufficient to rescue the sex reversal induced by disruption of Kdm6b This study establishes causality and a direct genetic link between epigenetic mechanisms and temperature-dependent sex determination in a turtle species.

Author Correction: Dmrt1 is required for primary male sexual differentiation in Chinese soft-shelled turtle Pelodiscus sinensis.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

Dmrt1 is required for primary male sexual differentiation in Chinese soft-shelled turtle Pelodiscus sinensis.

In vertebrates, the primary sex-determining signals that initiate sexual development are remarkably diverse, ranging from complete genetic to environmental cues. However, no sex determination-related genes have been functionally identified in reptiles. Here, we characterized a conserved DM domain gene, Dmrt1, in Chinese soft-shelled turtle Pelodiscus sinensis (P. sinensis), which exhibits ZZ/ZW sex chromosomes. Dmrt1 exhibited early male-specific embryonic expression, preceding the onset of gonadal sex differentiation. The expression of Dmrt1 was induced in ZW embryonic gonads that were masculinized by aromatase inhibitor treatment. Dmrt1 knockdown in ZZ embryos by RNA interference resulted in male to female sex reversal, characterized by obvious feminization of gonads, significant down-regulation of testicular markers Amh and Sox9, and remarkable up-regulation of ovarian regulators, Cyp19a1 and Foxl2. Conversely, ectopic expression of Dmrt1 led to largely masculinized genetic females, production of Amh and Sox9, and a decline in Cyp19a1 and Foxl2. These findings demonstrate that Dmrt1 is both necessary and sufficient to initiate testicular development, thereby acting as an upstream regulator of the male pathway in P. sinensis.

Dmrt1 induces the male pathway in a turtle species with temperature-dependent sex determination.

The molecular mechanism underlying temperature-dependent sex determination (TSD) has been a long-standing mystery; in particular, the thermosensitive genetic triggers for gonadal sex differentiation are largely unknown. Here, we have characterized a conserved DM domain gene, Dmrt1, in the red-eared slider turtle Trachemys scripta (T. scripta), which exhibits TSD. We found that Dmrt1 has a temperature-dependent, sexually dimorphic expression pattern, preceding gonadal sex differentiation, and is capable of responding rapidly to temperature shifts and aromatase inhibitor treatment. Most importantly, loss- and gain-of-function analyses provide solid evidence that Dmrt1 is both necessary and sufficient to initiate male development in T. scripta Furthermore, the DNA methylation dynamics of the Dmrt1 promoter are tightly correlated with temperature and could mediate the impact of temperature on sex determination. Collectively, our findings demonstrate that Dmrt1 is a candidate master male sex-determining gene in this TSD species, consistent with the idea that DM domain genes are conserved during the evolution of sex determination mechanisms.