Sex Lethal Gene Manipulates Gonadal Development of Medaka, , through Estrogenic Interventions.

Germ cells are pivotal for gonadal sexuality maintenance and reproduction. Sex lethal (), the somatic sex determining gene of , is the known regulator and initiator of germ cell femininity in invertebrates. However, the role of the Sxl homologue has rarely been investigated in vertebrates.

Testicular inducing steroidogenic cells trigger sex change in groupers.

Vertebrates usually exhibit gonochorism, whereby their sex is fixed throughout their lifetime. However, approximately 500 species (~ 2%) of extant teleost fishes change sex during their lifetime. Although phylogenetic and evolutionary ecological studies have recently revealed that the extant sequential hermaphroditism in teleost fish is derived from gonochorism, the evolution of this transsexual ability remains unclear.

Estrogen receptor 2b is the major determinant of sex-typical mating behavior and sexual preference in medaka.

Male and female animals typically display innate sex-specific mating behaviors, which, in vertebrates, are highly dependent on sex steroid signaling. While estradiol-17β (E2) signaling through estrogen receptor 2 (ESR2) serves to defeminize male mating behavior in rodents, the available evidence suggests that E2 signaling is not required in teleosts for either male or female mating behavior. Here, we report that female medaka deficient for Esr2b, a teleost ortholog of ESR2, are not receptive to males but rather court females, despite retaining normal ovarian function with an unaltered sex steroid milieu.

Male-predominant galanin mediates androgen-dependent aggressive chases in medaka.

Recent studies in mice demonstrate that a subset of neurons in the medial preoptic area (MPOA) that express galanin play crucial roles in regulating parental behavior in both sexes. However, little information is available on the function of galanin in social behaviors in other species. Here, we report that, in medaka, a subset of MPOA galanin neurons occurred nearly exclusively in males, resulting from testicular androgen stimulation.

Estrogen and estrogen receptors chauffeur the sex-biased autophagic action in liver.

Autophagy, or cellular self-digestion, is an essential cellular process imperative for energy homeostasis, development, differentiation, and survival. However, the intrinsic factors that bring about the sex-biased differences in liver autophagy are still unknown. In this work, we found that autophagic genes variably expresses in the steroidogenic tissues, mostly abundant in liver, and is influenced by the individual's sexuality.

Estrogen Receptor β2 Oversees Germ Cell Maintenance and Gonadal Sex Differentiation in Medaka, Oryzias latipes.

In vertebrates, estrogen receptors are essential for estrogen-associated early gonadal sex development. Our previous studies revealed sexual dimorphic expression of estrogen receptor β2 (ERβ2) during embryogenesis of medaka, and here we investigated the functional importance of ERβ2 in female gonad development and maintenance using a transgenerational ERβ2-knockdown (ERβ2-KD) line and ERβ2-null mutants. We found that ERβ2 reduction favored male-biased gene transcription, suppressed female-responsive gene expression, and affected SDF1a and CXCR4b co-assisted chemotactic primordial germ cell (PGC) migration.

Neuropeptide B mediates female sexual receptivity in medaka fish, acting in a female-specific but reversible manner.

Male and female animals display innate sex-specific mating behaviors. In teleost fish, altering the adult sex steroid milieu can effectively reverse sex-typical mating behaviors, suggesting remarkable sexual lability of their brains as adults. In the teleost medaka, neuropeptide B (NPB) is expressed female-specifically in the brain nuclei implicated in mating behavior.

Ovarian aromatase loss-of-function mutant medaka undergo ovary degeneration and partial female-to-male sex reversal after puberty.

Although estrogens have been generally considered to play a critical role in ovarian differentiation in non-mammalian vertebrates, the specific functions of estrogens during ovarian differentiation remain unclear. We isolated two mutants with premature stops in the ovarian aromatase (cyp19a1) gene from an N-ethyl-N-nitrosourea-based gene-driven mutagenesis library of the medaka, Oryzias latipes. In XX mutants, gonads first differentiated into normal ovaries containing many ovarian follicles that failed to accumulate yolk.

Hatching enzymes disrupt aberrant gonadal degeneration by the autophagy/apoptosis cell fate decision.

Environmental stressors, gonadal degenerative diseases and tumour development can significantly alter the oocyte physiology, and species fertility and fitness. To expand the molecular understanding about oocyte degradation, we isolated several spliced variants of Japanese anchovy hatching enzymes (AcHEs; ovastacin homologue) 1 and 2, and analysed their potential in oocyte sustenance. Particularly, AcHE1b, an ovary-specific, steroid-regulated, methylation-dependent, stress-responsive isoform, was neofunctionalized to regulate autophagic oocyte degeneration.

17β-HSD Type 12-Like Is Responsible for Maturation-Inducing Hormone Synthesis During Oocyte Maturation in Masu Salmon.

The maturation-inducing hormone 17α,20β-dihydroxy-4-pregnen-3-one (DHP) was first identified in the amago salmon. Although carbonyl reductase-like 20β-hydroxysteroid dehydrogenase (CR/20β-HSD) was reported to convert 17α-hydroxyprogesterone (17OHP) to DHP in rainbow trout, we previously found that CR/20β-HSD messenger RNA (mRNA) was not upregulated in stimulated granulosa cells from masu salmon, which suggested that DHP is synthesized by a different enzyme. Accordingly, the current study aimed to identify the specific 20β-hydroxysteroid dehydrogenase (20β-HSD) responsible for DHP production by granulosa cells during final oocyte maturation in masu salmon.

Autosomal gsdf acts as a male sex initiator in the fish medaka.

Sex is pivotal for reproduction, healthcare and evolution. In the fish medaka, the Y-chromosomal dmy (also dmrt1bY) serves the sex determiner, which activates dmrt1 for male sex maintenance. However, how dmy makes the male decision via initiating testicular differentiation has remained unknown.

Rspo1-activated signalling molecules are sufficient to induce ovarian differentiation in XY medaka (Oryzias latipes).

In contrast to our understanding of testicular differentiation, ovarian differentiation is less well understood in vertebrates. In mammals, R-spondin1 (Rspo1), an activator of Wnt/β-catenin signaling pathway, is located upstream of the female sex determination pathway. However, the functions of Rspo1 in ovarian differentiation remain unclear in non-mammalian species.

Expression Patterns of CREBs in Oocyte Growth and Maturation of Fish.

In fish, oocyte meiotic maturation is regulated by 17α, 20β-dihydroxy-progesterone through cAMP. To study the role of cAMP response element binding protein (CREB) in meiotic maturation, we cloned and characterized the expression pattern of CREBs from two fish models, the Nile tilapia and catfish. In the Nile tilapia three different CREBs were identified where in CREB1 was found in many tissues including gonads with abundant expression in testis.

A Tandem Duplicate of Anti-Müllerian Hormone with a Missense SNP on the Y Chromosome Is Essential for Male Sex Determination in Nile Tilapia, Oreochromis niloticus.

Variation in the TGF-β signaling pathway is emerging as an important mechanism by which gonadal sex determination is controlled in teleosts. Here we show that amhy, a Y-specific duplicate of the anti-Müllerian hormone (amh) gene, induces male sex determination in Nile tilapia. amhy is a tandem duplicate located immediately downstream of amhΔ-y on the Y chromosome.

Gonadal soma-derived factor (gsdf), a TGF-beta superfamily gene, induces testis differentiation in the teleost fish Oreochromis niloticus.

The Nile tilapia, Oreochromis niloticus, is a gonochoristic teleost fish with an XX/XY genetic system and is an excellent model for gonadal sex differentiation. In the present study, we screened novel genes that were expressed predominantly in either XY or XX undifferentiated gonads during the critical period for differentiation of gonads into ovaries or testes using microarray screening. We focused on one of the isolated 12 candidate genes, #9475, which was an ortholog of gsdf (gonadal soma-derived factor), a member of the transforming growth factor-beta superfamily.

Starvation beneficially influences the liver physiology and nutrient metabolism in Edwardsiella tarda infected red sea bream (Pagrus major).

Dietary compromises, especially food restrictions, possess species-specific effects on the health status and infection control in several organisms, including fish. To understand the starvation-mediated physiological responses in Edwardsiella tarda infected red sea bream, especially in the liver, we performed a 20-day starvation experiment using 4 treatment (2 fed and 2 starved) groups, namely, fed-placebo, starved-placebo, fed-infected, and starved-infected, wherein bacterial exposure was done on the 11th day. In the present study, the starved groups showed reduced hepatosomatic index and drastic depletion in glycogen storage and vacuole formation.

A new relaxin-like gonad-stimulating peptide identified in the starfish Asterias amurensis.

Relaxin-like gonad-stimulating peptide (RGP) of starfish Asterina pectinifera was the first invertebrate gonadotropin to have its chemical structure identified. However, it is unclear whether gonadotropic hormones in other species starfish are relaxin-like peptides. Thus, this study tried to identify the molecular structure of gonadotropic hormone in Asterias amurensis.

Figla Favors Ovarian Differentiation by Antagonizing Spermatogenesis in a Teleosts, Nile Tilapia (Oreochromis niloticus).

Figla (factor in the germ line, alpha), a female germ cell-specific transcription factor, had been shown to activate genetic hierarchies in oocytes. The ectopic expression of Figla was known to repress spermatogenesis-associated genes in male mice. However, the potential role of Figla in other vertebrates remains elusive.

A syntenic region conserved from fish to Mammalian x chromosome.

Sex chromosomes bearing the sex-determining gene initiate development along the male or female pathway, no matter which sex is determined by XY male or ZW female heterogamety. Sex chromosomes originate from ancient autosomes but evolved rapidly after the acquisition of sex-determining factors which are highly divergent between species. In the heterogametic male system (XY system), the X chromosome is relatively evolutionary silent and maintains most of its ancestral genes, in contrast to its Y counterpart that has evolved rapidly and degenerated.

Steroid responsive regulation of IFNγ2 alternative splicing and its possible role in germ cell proliferation in medaka.

Interferon gamma (IFNγ) is an active player in estrogen dependent immuno-regulation of fish. The present work was aimed to characterize the alternatively spliced isoforms of IFNγ2 in the gonadal sex development in medaka. Phylogenetic analysis demonstrated that IFNγ2a and 2b were clustered with fish specific interferon gamma.

Gene replacement by zinc finger nucleases in medaka embryos.

Gene replacement (GR) via homologous recombination is a powerful tool for genome editing. Recently, direct GR is achieved successfully by coinjection of mRNAs for engineered endonucleases such as zinc finger nucleases (ZFNs) and donor DNA in developing embryos of diverse organisms. Here, we report the procedures and efficiency for direct GR by using ZFNs in the fish medaka.

Sexually dimorphic expression of the sex chromosome-linked genes cntfa and pdlim3a in the medaka brain.

In vertebrates, sex differences in the brain have been attributed to differences in gonadal hormone secretion; however, recent evidence in mammals and birds shows that sex chromosome-linked genes, independent of gonadal hormones, also mediate sex differences in the brain. In this study, we searched for genes that were differentially expressed between the sexes in the brain of a teleost fish, medaka (Oryzias latipes), and identified two sex chromosome genes with male-biased expression, cntfa (encoding ciliary neurotrophic factor a) and pdlim3a (encoding PDZ and LIM domain 3 a). These genes were found to be located 3-4 Mb from and on opposite sides of the Y chromosome-specific region containing the sex-determining gene (the medaka X and Y chromosomes are genetically identical, differing only in this region).

Transdifferentiation of differentiated ovary into functional testis by long-term treatment of aromatase inhibitor in Nile tilapia.

Females with differentiated ovary of a gonochoristic fish, Nile tilapia, were masculinized by long-term treatment with an aromatase inhibitor (Fadrozole) in the present study. The reversed gonads developed into functional testes with fertile sperm. The longer the fish experienced sex differentiation, the longer treatment time was needed for successful sex reversal.

Neuropeptide B is female-specifically expressed in the telencephalic and preoptic nuclei of the medaka brain.

In the brain of medaka (Oryzias latipes), a teleost fish, we recently found that the supracommissural/posterior nuclei of the ventral telencephalic area (Vs/Vp) and the magnocellular/gigantocellular portions of the magnocellular preoptic nucleus (PMm/PMg) express estrogen receptor (ER) and androgen receptor (AR) specifically in females. This finding led us to postulate that sex steroid hormones might induce gene expression unique to females in these nuclei. In the present study, we searched for genes differentially expressed between the sexes in the medaka brain and identified the gene encoding neuropeptide B (npb) as being female-specifically expressed in Vs/Vp and PMm/PMg.