Sakura Tanaka

All Publications

• Role of gonadal soma-derived growth factor (gsdf) on sex-differentiation in Nile tilapia, Oreochromis niloticus. General and comparative endocrinology Arai, T., Tanaka, S., Sakon, M., Gao, H., Ijiri, S. 2026: 114884

  Abstract

  Molecular sex differentiation is regulated by complex transcriptional dynamics. In Nile tilapia, ovarian differentiation requires the synthesis of estradiol-17β (E2), in which forkhead box L2 (foxl2) and ovarian aromatase (cytochrome P450, family 19, subfamily A, polypeptide 1a; cyp19a1a) play critical roles, whereas gonadal soma-derived growth factor (gsdf) and doublesex and mab-3-related transcription factor 1 (dmrt1) are implicated in testicular differentiation. During the early phase of molecular sex differentiation, gsdf mRNA is expressed to a significantly higher degree in the undifferentiated gonads of XY males than in XX females. However, the molecular mechanisms by which gsdf promotes testicular differentiation remain poorly understood. We hypothesized that gsdf acts by suppressing ovarian differentiation or promoting testicular differentiation through the upregulation of dmrt1. To clarify the relationship with dmrt1, we performed fluorescent double in situ hybridization on undifferentiated gonads and testes. Furthermore, recombinant Gsdf (rGsdf) was produced and microinjected into the body cavity of XX larvae to investigate its effects on the expression of sex differentiation-related genes in undifferentiated gonads. We demonstrated that gsdf and dmrt1 were expressed in distinct cell populations in undifferentiated gonads, whereas partial co-localization occurred in certain cells within the testes. Administration of rGsdf led to a significant decrease in the expression of E2 synthesis-related genes, including foxl2, hydroxysteroid 17-beta dehydrogenase 1 (hsd17b1), and cyp19a1a. These findings suggest that gsdf suppresses E2 production and that its expression is regulated not only by dmrt1 but also by other factors during the molecular sex differentiation phase in Nile tilapia.

  View details for DOI 10.1016/j.ygcen.2026.114884

  View details for PubMedID 41534571

• Gonadotropin releasing hormone - gonadotropes interactions revealed by pituitary single-cell transcriptomics in zebrafish. Endocrinology Tanaka, S., Yu, Y., Levavi-Sivan, B., Zmora, N., Zohar, Y. 2024

  Abstract

  Gonadotropin-releasing hormone (GnRH) governs reproduction by regulating pituitary gonadotropins. Unlike most vertebrates, gnrh-/- zebrafish are fertile. To elucidate the role of the hypophysiotropic-Gnrh3 and other mechanisms regulating pituitary gonadotropes, we profiled the gene expression of all individual pituitary cells of wild-type and gnrh3-/- adult female zebrafish. The single-cell RNA-Seq showed that Lh and Fsh gonadotropes express the two gonadotropin beta subunits with a ratio of 140:1 (lhb:fshb) and 4:1 (fshb:lhb), respectively. Lh gonadotropes predominantly express genes encoding receptors for Gnrh (gnrhr2), thyroid hormone, estrogen, and steroidogenic factor 1 (SF1). No Gnrh receptor transcript was enriched in Fsh gonadotropes. Instead, cholecystokinin receptor-b and galanin receptor-1b transcripts were enriched in these cells. The loss of Gnrh3 gene in gnrh3-/- zebrafish resulted in downregulation of fshb in Lh gonadotropes and upregulation of pituitary hormones like thyroid-stimulating hormone, growth hormone, prolactin and proopiomelanocortin-a. Likewise, targeted chemogenetic ablation of Gnrh3 neurons led to a decrease in the number of fshb+, lhb+ and fshb+/lhb+ cells. Our studies suggest that Gnrh3 directly acts on Lh gonadotropes through Gnrhr2, but the outcome of this interaction is still unknown. Gnrh3 also regulates fshb expression in both gonadotropes, most likely via a non-Gnrh receptor route. Altogether, while Lh secretion and synthesis are likely regulated in a Gnrh-independent manner, Gnrh3 seems to play a role in the cellular organization of the pituitary. Moreover, the co-expression of lhb and fshb in both gonadotropes provides a possible explanation as to why gnrh3-/- zebrafish are fertile.

  View details for DOI 10.1210/endocr/bqae151

  View details for PubMedID 39499852

• Loss of function of Vasoactive-intestinal peptide alters sex ratio and reduces male reproductive fitness in zebrafish. Endocrinology Yu, Y., Tanaka, S., Wong, T. T., Zohar, Y., Zmora, N. 2024

  Abstract

  Vasoactive-intestinal peptide (Vip) is a pleiotropic peptide with a wide range of distribution and functions. Zebrafish possess two isoforms of Vip (a and b), in which Vipa is most homologous to the mammalian form. In female zebrafish, Vipa can stimulate LH secretion from the pituitary but is not essential for female reproduction, as vipa-/- females display normal reproduction. In contrast, we have found that vipa-/- males are severely sub-fertile and sex ratio of offspring is female-biased. By analyzing all aspects of male reproduction with WT males, we show that the testes of vipa-/- are underdeveloped and contain ∼70% less spermatids compared to WT counterparts. The sperm of vipa-/- males displayed reduced potency in terms of fertilization (by ∼80%) and motility span and duration (by ∼50%). In addition, vipa-/- male attraction to WT females was largely non-existent, indicating decreased sexual motivation. We show that vipa mRNA and protein is present in Leydig cells and in developing germ cells in the testis of WT, raising the possibility that endogenous Vipa contributes to testicular function. Absence of Vipa in vipa-/- males resulted in downregulation of three key genes in the androgen synthesis chain in the testis, 3β-hsd, 17β-hsd1 and cyp11c1 (11β-hydrogenase), associated with a pronounced decrease in 11-ketotestosterone production and, in turn, compromised reproductive fitness. Altogether, this study establishes a crucial role for Vipa in the regulation of male reproduction in zebrafish, like in mammals, with the exception that Vipa is also expressed in zebrafish testis.

  View details for DOI 10.1210/endocr/bqae082

  View details for PubMedID 38984720

• Chemogenetic Depletion of Hypophysiotropic GnRH Neurons Does Not Affect Fertility in Mature Female Zebrafish INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES Tanaka, S., Zmora, N., Levavi-Sivan, B., Zohar, Y. 2022; 23 (10)

  Abstract

  The hypophysiotropic gonadotropin-releasing hormone (GnRH) and its neurons are crucial for vertebrate reproduction, primarily in regulating luteinizing hormone (LH) secretion and ovulation. However, in zebrafish, which lack GnRH1, and instead possess GnRH3 as the hypophysiotropic form, GnRH3 gene knockout did not affect reproduction. However, early-stage ablation of all GnRH3 neurons causes infertility in females, implicating GnRH3 neurons, rather than GnRH3 peptides in female reproduction. To determine the role of GnRH3 neurons in the reproduction of adult females, a Tg(gnrh3:Gal4ff; UAS:nfsb-mCherry) line was generated to facilitate a chemogenetic conditional ablation of GnRH3 neurons. Following ablation, there was a reduction of preoptic area GnRH3 neurons by an average of 85.3%, which was associated with reduced pituitary projections and gnrh3 mRNA levels. However, plasma LH levels were unaffected, and the ablated females displayed normal reproductive capacity. There was no correlation between the number of remaining GnRH3 neurons and reproductive performance. Though it is possible that the few remaining GnRH3 neurons can still induce an LH surge, our findings are consistent with the idea that GnRH and its neurons are likely dispensable for LH surge in zebrafish. Altogether, our results resurrected questions regarding the functional homology of the hypophysiotropic GnRH1 and GnRH3 in controlling ovulation.

  View details for DOI 10.3390/ijms23105596

  View details for Web of Science ID 000804301500001

  View details for PubMedID 35628411

  View details for PubMedCentralID PMC9143870

• Vasoactive Intestinal Peptide Indirectly Elicits Pituitary LH Secretion Independent of GnRH in Female Zebrafish ENDOCRINOLOGY Tanaka, S., Zmora, N., Levavi-Sivan, B., Zohar, Y. 2022; 163 (2)

  Abstract

  Vasoactive intestinal peptide (Vip) regulates luteinizing hormone (LH) release through the direct regulation of gonadotropin-releasing hormone (GnRH) neurons at the level of the brain in female rodents. However, little is known regarding the roles of Vip in teleost reproduction. Although GnRH is critical for fertility through the regulation of LH secretion in vertebrates, the exact role of the hypophysiotropic GnRH (GnRH3) in zebrafish is unclear since GnRH3 null fish are reproductively fertile. This phenomenon raises the possibility of a redundant regulatory pathway(s) for LH secretion in zebrafish. Here, we demonstrate that VipA (homologues of mammalian Vip) both inhibits and induces LH secretion in zebrafish. Despite the observation that VipA axons may reach the pituitary proximal pars distalis including LH cells, pituitary incubation with VipA in vitro, and intraperitoneal injection of VipA, did not induce LH secretion and lhβ mRNA expression in sexually mature females, respectively. On the other hand, intracerebroventricular administration of VipA augmented plasma LH levels in both wild-type and gnrh3-/- females at 1 hour posttreatment, with no observed changes in pituitary GnRH2 and GnRH3 contents and gnrh3 mRNA levels in the brains. While VipA's manner of inhibition of LH secretion has yet to be explored, the stimulation seems to occur via a different pathway than GnRH3, dopamine, and 17β-estradiol in regulating LH secretion. The results indicate that VipA induces LH release possibly by acting with or through a non-GnRH factor(s), providing proof for the existence of functional redundancy of LH release in sexually mature female zebrafish.

  View details for DOI 10.1210/endocr/bqab264

  View details for Web of Science ID 000753587100018

  View details for PubMedID 34978328

• Effects of Infectious Diseases on Population Dynamics of Marine Organisms in Chesapeake Bay ESTUARIES AND COASTS Jesse, J. A., Agnew, M., Arai, K., Armstrong, C., Hood, S. M., Kachmar, M. L., Long, J. T., McCarty, A. J., Ross, M. O., Rubalcava, K. D., Shaner, J., Tanaka, S., Wood, L., Schott, E. J., Wilberg, M. J. 2021; 44 (8): 2334-2349

  View details for DOI 10.1007/s12237-021-00915-4

  View details for Web of Science ID 000632318100001