Insulin-like growth factor binding proteins inhibit oocyte maturation of zebrafish.

The function of insulin-like growth factor (Igf) system in ovary has attracted much attention, but the role of Igf binding proteins (Igfbps) in ovary is still largely unknown. In this study, the role of Igfbps in oocyte maturation was investigated in zebrafish. The expression of all eight identified Igfbps except Igfbp6b could be detected in the adult ovary and exhibited differential expression profiles during folliculogenesis. The expression of several Igfbps is dynamically changed during oocyte maturation induced by human chorionic gonadotropin (hCG). By treatment of an Igfbps inhibitor NBI-31772 in vitro, the oocyte maturation could be stimulated in a clear dose-, time- and stage-dependent manner. Such effects were also observed by administration of NBI-31772 in vivo. Igfbps are differentially expressed in both follicular cells and oocytes, but the effect of NBI-31772 could only be found in intact follicles and not in the denuded oocytes. Previous studies have demonstrated that Igf3 is the major Igf member in regulating oocyte maturation of zebrafish. Interestingly, NBI-31772 could increase the effect of Igf3 on oocyte maturation. Furthermore, we found the effect of NBI-31772 on oocyte maturation could be blocked by an Igf type 1 receptor inhibitor BMS-536924 in vitro, suggesting the Igfbps can inhibit the oocyte maturation via Igf/Igf1r pathway. Together, we provided the first evidence in fish that Igfbps inhibit oocyte maturation of zebrafish.

Li J ，Wang Y ，Kang T ，Li X ，Niu C ... -  《-》

IGFs mediate the action of LH on oocyte maturation in zebrafish.

Li J ，Chu L ，Sun X ，Liu Y ，Cheng CH ... -  《-》

Expression of two insulin receptor subtypes, insra and insrb, in zebrafish (Danio rerio) ovary and involvement of insulin action in ovarian function.

Present study reports differential expression of the two insulin receptor (IR) subtypes in zebrafish ovary at various stages of follicular growth and potential involvement of IR in insulin-induced oocyte maturation. The results showed that mRNA expression for IR subtypes, insra and insrb, exhibited higher levels in mid-vitellogenic (MV) and full-grown (FG) rather than pre-vitellogenic (PV) oocytes. Interestingly, compared to the levels in denuded oocytes, mRNAs for both insra and insrb were expressed at much higher level in the follicle layer harvested from FG oocytes. Immunoprecipitation using IRβ antibody could detect a protein band of desired size (∼95kDa) in FG oocyte lysates. Further, IRβ immunoreactivity was detected in ovarian tissue sections, especially at the follicle layer and oocyte membrane of MV and FG, but not PV stage oocytes. While hCG (10IU/ml) stimulation was without effect, priming with insulin (5μM) could promote oocyte maturation of MV oocytes in a manner sensitive to de novo protein and steroid biosynthesis. Compared to hCG, in insulin pre-incubated MV oocytes, stimulation with maturation inducing steroid (MIS), 17α,20β-dihydroxy-4-pregnen-3-one (DHP) elicited higher maturational response. Potential involvement of insulin-mediated action on acquisition of maturational competence and regulation of oocyte maturation was further manifested through up regulation of 20β-hydroxysteroid dehydrogenase (20β-hsd), MIS receptor (mPRα), insulin-like growth factor 3 (igf3) and IGF1 receptor (igf1rb), but not cyp19a expression in MV oocytes. Moreover, priming with anti-IRβ attenuated insulin action on meiotic G2-M1 transition indicating the specificity of insulin action and physiological relevance of IR in zebrafish ovary.

Das D ，Nath P ，Pal S ，Hajra S ，Ghosh P ，Maitra S ... -  《-》

Insulin-like growth factor 3 is involved in oocyte maturation in zebrafish.

Li J ，Liu Z ，Wang D ，Cheng CH ... -  《-》

Characterization and regulation of the insulin-like growth factor (IGF) system in the zebrafish (Danio rerio) ovary.

Locally produced peptide hormones play an important role in the paracrine/autocrine regulation of ovarian development. The insulin-like growth factor (IGF) system is one family of local factors that has not been well studied in the ovary of fish. This study characterized the zebrafish (Danio rerio) ovarian IGF system, its spatial and temporal expression and regulation by gonadotropins and steroids. Three ligands (igf2a, igf2b, igf3) and two receptors (igf1ra and igf1rb) were demonstrated in the ovary using RT-qPCR. Though it was examined, igf1 expression was not detected in the zebrafish ovary. Igf3 expression significantly decreased in the hours prior to ovulation and was confined to the follicle cells. Igf2a, igf2b and the two receptors were detected in both the follicle cells and the oocyte and were constitutively expressed in ovarian tissue across the daily ovulatory cycle. In vitro addition of human chorionic gonadotropin (hCG; 20 IU/ml) stimulated a significant increase in igf3 expression in both midvitellogenic (MV; 0.45-0.56 mm) and full grown (FG; 0.57-0.65 mm) follicles while igf2b expression increased only in FG follicles. Treatment of follicles in vitro with 17alpha,20beta-dihydroxy-4-pregnen-3-one (17,20beta-P; 10 ng/ml) significantly decreased igf3 and igf2b expression in both MV and FG follicles. 17beta-Estradiol (E(2); 25 ng/ml) had no effect on the expression of igf3 in MV or FG follicles. Igf1rb expression did not change after treatment with hCG, 17,20beta-P or E(2). Collectively, these results demonstrate the presence of an ovarian IGF system in zebrafish that is differentially regulated by gonadotropin and steroids.

Nelson SN ，Van Der Kraak G 《-》