Okamura Ayako, Masumoto Ayane, Takenouchi Atsushi, Kudo Toshiyuki, Aizawa Sayaka, Ogoshi Maho, Takahashi Sumio, Tsudzuki Masaoki, Takeuchi Sakae
Department of Biology, Faculty of Science, Okayama University, 3-1-1 Kitaku, Tsushimanaka, Okayama 700-8530, Japan.
Graduate School of Biosphere Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8528, Japan; Japanese Avian Bioresource Project Research Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8528, Japan.
Gen Comp Endocrinol. 2019 Feb 1;272:109-116. doi: 10.1016/j.ygcen.2018.12.011. Epub 2018 Dec 27.
Chicken early (EF) and late feathering (LF) are sex-linked phenotypes conferred by wild-type k and dominant K alleles on chromosome Z, respectively. Besides prolactin (PRL) receptor (PRLR) and sperm flagellar 2 (SPEF2) genes, the K allele contains a fusion gene in which partially duplicated PRLR (dPRLR) and SPEF2 (dSPEF2) genes are linked in a tail-to-tail manner. The causative dPRLR gene encodes a C-terminal truncated receptor. LF chickens have short or no primaries at hatching; however, their feather growth rate is higher than that of EF chickens. This study aimed to elucidate the molecular basis of the K allele's biphasic effect on feather development. By 3'RACE and RT-PCR analyses, we demonstrated that dSPEF2 gene transcription occurred beyond all coding exons of the dPRLR gene on the opposite strand and that dPRLR mRNA was less abundant than PRLR mRNA. In addition, a 5'UTR splice variant (SPV) of PRL receptor mRNAs was increased in LF chickens. In vitro expression analysis of 5'UTR linked to the luciferase reporter gene revealed higher translation efficiency of SPV. RT-qPCR showed that the dPRLR mRNA level was higher in embryos; conversely, SPV was higher in hatched chickens, as was dSPEF2 mRNA. These findings suggest that the K allele inhibits feather development at the fetal stage by expressing dPRLR to attenuate PRLR function and promotes feather growth after hatching by increasing PRLR through dSPEF2 mRNA expression. Increased SPV may cause greater feather growth than that in EF chickens by increasing the availability of PRLR homodimers and enhancing PRL signaling.
鸡的早羽（EF）和晚羽（LF）是分别由Z染色体上的野生型k和显性K等位基因赋予的性连锁表型。除催乳素（PRL）受体（PRLR）和精子鞭毛2（SPEF2）基因外，K等位基因包含一个融合基因，其中部分重复的PRLR（dPRLR）和SPEF2（dSPEF2）基因以尾对尾的方式相连。致病的dPRLR基因编码一种C末端截短的受体。LF鸡在孵化时初级飞羽短或无；然而，它们的羽毛生长速度高于EF鸡。本研究旨在阐明K等位基因对羽毛发育双相作用的分子基础。通过3'RACE和RT-PCR分析，我们证明dSPEF2基因转录发生在相反链上dPRLR基因的所有编码外显子之外，且dPRLR mRNA的丰度低于PRLR mRNA。此外，LF鸡中PRL受体mRNA的5'UTR剪接变体（SPV）增加。与荧光素酶报告基因相连的5'UTR的体外表达分析显示SPV具有更高的翻译效率。RT-qPCR表明胚胎中dPRLR mRNA水平较高；相反，孵化后的鸡中SPV较高，dSPEF2 mRNA也是如此。这些发现表明，K等位基因通过表达dPRLR以减弱PRLR功能在胎儿期抑制羽毛发育，并通过dSPEF2 mRNA表达增加PRLR在孵化后促进羽毛生长。增加的SPV可能通过增加PRLR同二聚体的可用性和增强PRL信号传导，导致比EF鸡更大的羽毛生长。
