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Nodal, a member of the transforming growth factor-β (TGF-β) superfamily, plays critical roles during embryo development. Several studies suggest that Nodal also regulates reproduction. The objective of this study was to investigate if Nodal is expressed in zebrafish ovary and if it is involved in the regulation of ovarian functions. Using real-time PCR, we detected two Nodal homologs, nodal-related (ndr)1, and ndr2 in zebrafish ovarian follicles. We further compared the mRNA levels of ndr1, ndr2, and their receptors between maturational incompetent early vitellogenic follicles (stage IIIa) and mid- to late-vitellogenic follicles (stage IIIb) which are capable of undergoing maturation when they are induced by hormones. We found that mRNAs for ndr1 and ndr2, as well as a type I receptor, acvr1ba, were significantly increased in follicular cells isolated from stage IIIb follicles. In primary cultures of ovarian follicular cells, treatment with recombinant human Nodal inhibited cell proliferation. On the other hand, Nodal increased the mRNA levels of two steroidogenic enzymes hsd3b2 and cyp17a1, as well as paqr8, which encodes the membrane progestin receptor-β (mPR-β). Conversely, knockdown of ndr1 and ndr2 using siRNAs decreased the mRNA levels of hsd3b2, cyp17a1, and paqr8. Finally, treatment of Nodal significantly induced oocyte maturation. Taken together, these findings suggest that Nodal exerts multiple effects on zebrafish ovary to regulate follicle growth, steroidogenesis, and oocyte maturation., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Thyroid development has been intensively studied in the mouse, where it closely recapitulates the human situation. Despite the lack of a compact thyroid gland, the zebrafish thyroid tissue originates from the pharyngeal endoderm and the main genes involved in its patterning and early development are conserved between zebrafish and mammals. In recent years, the zebrafish has become a powerful model not only for the developmental biology studies, but also for large-scale genetic analyses and drug screenings, mostly thanks to the ease with which its embryos can be manipulated and to its translucent body, which allows in vivo imaging. In this review we will provide an overview of the current knowledge of thyroid gland origin and differentiation in the zebrafish. Moreover, we will consider the action of thyroid hormones and some aspects related to endocrine disruptors.