Elucidation of reproductive endocrine system in hagfish

盲鳗被认为是已知的最原始的脊椎动物，无论是现存的还是灭绝的，研究它们的繁殖对于理解脊椎动物生殖内分泌系统的进化方面都很重要。最近，在盲鳗脑垂体中发现了单一功能的GTH。本研究从盲鳗睾丸中克隆了细胞色素P450侧链切割酶（CYP11A）。在两性中，CYP11A mRNA水平与性腺发育之间存在明显的正相关。此外，盲鳗GTH刺激了培养睾丸中CYP11A mRNA的水平。从盲鳗下丘脑中鉴定出的PQRFamide肽被证明可以刺激盲鳗垂体中GTH mRNA的水平。本研究进一步表明在下丘脑-垂体水平存在类固醇（雌二醇）反馈系统。这表明，脊椎动物在其早期进化过程中，已经建立了下丘脑-垂体-性腺轴。

Since hagfishes are considered the most primitive vertebrate known, living or extinct, studies on their reproduction are important for understanding the evolutionary aspects of the vertebrate reproductive endocrine system. Recently, single functional GTH was identified in the hagfish pituitary gland. In the present study, cytochrome P450 side-chain cleavage enzyme (CYP11A) was cloned from the hagfish testis. A clear positive correlation was noted between CYP11A mRNA levels and gonadal development in both sexes. Moreover, hagfish GTH stimulated CYP11A mRNA levels in the cultured testis. A PQRFamide peptide identified from the hagfish hypothalamus was shown to stimulate GTH mRNA levels in the hagfish pituitary. The present study further showed the presence of a steroid (estradiol) feedback system at the hypothalamic-pituitary levels. It is suggested that vertebrates, during their early evolution, have established the hypothalamic-pituitary-gonadal axis.