Exogenous GDF9 but not Activin A, BMP15 or TGFβ alters tight junction protein transcript abundance in zebrafish ovarian follicles

The tight junction (TJ) complex plays an important role in regulating paracellular permeability and provides mechanical stability in vertebrate epithelia and endothelia. In zebrafish ovarian follicles, TJ complexes in the follicular envelope degenerate as the follicles develop towards maturation. In the current study, transcript abundance of claudins (cldn d, g, h, 1, and 12) and occludins (ocln, and ocln b) were assessed in mid-vitellogenic follicles in response to treatment with exogenous growth factors that are reported to be involved in zebrafish follicle development (i.e. Activin A, BMP15, GDF9 and TGFβ). Exogenous GDF9 reduced the transcript abundance of cldn g, ocln and ocln b in mid-vitellogenic follicles, whereas Activin A, BMP15, and TGFβ had no effect. Subsequent studies with GDF9 revealed that this factor did not alter TJ protein transcript abundance in pre-vitellogenic follicles but did increase the abundance of ocln b in fully grown (maturing) follicles. GDF9 was also seen to increase the abundance of StAR mRNA in all but primary stage follicles. These data suggest a role for GDF9 in the regulation of TJ integrity in zebrafish ovarian follicles, perhaps in the facilitation of ovulation, and support a previously postulated role for GDF9 in zebrafish ovarian follicle development. In addition, data also support the idea that endocrine factors play an important role in the regulation of TJ proteins during ovarian follicle development.

Research highlights
► GDF9 regulates claudin g, occludin and occludin b in zebrafish ovarian follicles.
► GDF9 regulates StAR expression in zebrafish ovarian follicles.
► TJ complexes in zebrafish ovarian follicles are regulated by endocrine factors.