Analyses of mRNA Expression Levels of Pituitary Hormones, Their Hypothalamic Regulating Factors, and Receptors Involved in Metamorphosis with Special Reference to the Summer and Winter Seasons

Zoolog Sci. 2024 Feb;41(1):32-38. doi: 10.2108/zs230080.ABSTRACTBullfrog (Rana catesbeiana) larvae inhabiting the main island of Japan overwinter as preclimax animals, whereas the larvae that reached climax in summer complete metamorphosis. We analyzed the mRNA expression levels of the adenohypophyseal hormones, hypothalamic hormones, and their receptors that are involved in controlling metamorphosis in tadpoles at various developmental stages available in summer and winter in order to understand the hormonal mechanism regulating metamorphosis progression. Corticotropin-releasing factor (CRF) and thyrotropin β-subunit (TSHβ) mRNA expression was enhanced as they reached the climax stage in metamorphosing summer tadpoles, although type 2 CRF receptor (CRFR2) mRNA levels demonstrated a tendency of elevation, indicating the activation of the hypothalamo-hypophyseal axis for stimulating the release of thyroid hormone in summer. Arginine vasotocin (AVT) mRNA levels were elevated as metamorphosis progressed, but mRNA expression levels were not synchronized with those of proopiomelanocortin (POMC) and V1b-type AVT receptor (V1bR). The elevation of mRNA levels of prolactin (PRL) 1A and type 3 thyrotropin-releasing hormone receptor (TRHR3), but not of thyrotropin-releasing hormone (TRH) precursor mRNA levels, was noted in climactic tadpoles, indicating that PRL mRNA levels are not simply dependent on the expression levels of TRH precursor mRNA. In the preclimactic larvae captured in ...
Source: Zoological Science - Category: Zoology Authors: Source Type: research