Ovarian expression and function of neuropeptide systems in teleosts and anurans.

Abstract

The hypothalamic-pituitary-gonadal axis regulates reproduction, sexual maturation, and spawning behaviours. Its evolutionary origins trace back to primitive jawless fish and has been well characterized in teleosts. Recent advances in multi-species genome sequencing, annotation, and experimental approaches for identifying and characterizing key regulators have advanced understanding of neuroendocrine regulation in teleost reproduction, reshaping existing models. Early studies in amphibians established that steroids are critical regulators of final oocyte maturation. Subsequent work in anurans revealed complex interactions among theca cells, follicular cells, and oocytes, supporting a three-cell model in which oocytes contribute to their own steroidogenic environment, challenging the traditional two-cell view of ovarian steroidogenesis. In teleosts, however, direct evidence that oocytes support steroid precursor delivery to theca and follicular cells is limited, and whether a comparable three-cell model applies remains an open hypothesis. Across both taxa, the roles of locally produced neuropeptides in coordinating interactions among theca cells, follicular cells, and oocytes remain largely uncharacterized. Here, we provide a short review of the localization and potential autocrine/paracrine functions of neuropeptides in teleost and amphibian ovaries and discuss existing knowledge gaps. We identify opportunities to leverage detailed localization studies that map neuropeptides to specific ovarian cell types and developmental stages, and discuss how integrating traditional and emerging experimental approaches can advance comparative studies in ovarian endocrinology. This work will improve our understanding of reproductive regulation in fishes and frogs, with applications in captive breeding, aquaculture, and endocrine disruption research.