Data_Sheet_1_Analysis of the Role of the Mc4r System in Development, Growth, and Puberty of Medaka.pdf

In mammals the melanocortin 4 receptor (Mc4r) signaling system has been mainly associated with the regulation of appetite and energy homeostasis. In fish of the genus Xiphophorus (platyfish and swordtails) puberty onset is genetically determined by a single locus, which encodes the mc4r. Wild populations of Xiphophorus are polymorphic for early and late-maturing individuals. Copy number variation of different mc4r alleles is responsible for the difference in puberty onset. To answer whether this is a special adaptation of the Mc4r signaling system in the lineage of Xiphophorus or a more widely conserved mechanism in teleosts, we studied the role of Mc4r in reproductive biology of medaka (Oryzias latipes), a close relative to Xiphophorus and a well-established model to study gonadal development. To understand the potential role of Mc4r in medaka, we characterized the major features of the Mc4r signaling system (mc4r, mrap2, pomc, agrp1). In medaka, all these genes are expressed before hatching. In adults, they are mainly expressed in the brain. The transcript of the receptor accessory protein mrap2 co-localizes with mc4r in the hypothalamus in adult brains indicating a conserved function of modulating Mc4r signaling. Comparing growth and puberty between wild-type and mc4r knockout medaka revealed that absence of Mc4r does not change puberty timing but significantly delays hatching. Embryonic development of knockout animals is retarded compared to wild-types. In conclusion, the Mc4r system in medaka is involved in regulation of growth rather than puberty.

在哺乳动物中，黑皮质素4受体（melanocortin 4 receptor, Mc4r）信号通路主要与食欲及能量稳态的调控相关。在剑尾鱼属（Xiphophorus，包括月光鱼和剑尾鱼）的鱼类中，青春期启动由单个遗传位点决定，该位点编码mc4r基因。剑尾鱼属的野生种群存在早熟与晚熟个体的多态性，不同mc4r等位基因的拷贝数变异是导致青春期启动时间差异的原因。为探究这一现象究竟是剑尾鱼属内Mc4r信号通路的特异性适应，还是硬骨鱼中更为广泛存在的保守机制，本研究以与剑尾鱼属亲缘关系较近、且作为性腺发育研究经典模型的青鳉（Oryzias latipes）为对象，探讨了Mc4r在其生殖生物学中的作用。为明确Mc4r在青鳉中的潜在功能，本研究对Mc4r信号通路的核心基因（mc4r、mrap2、pomc、agrp1）的主要特征进行了表征。青鳉体内上述所有基因均在孵化前表达，而成体中这些基因主要于脑组织内表达。成体大脑下丘脑区域中，受体辅助蛋白mrap2的转录本与mc4r共定位，这提示二者具有保守的Mc4r信号通路调控功能。通过对比野生型与mc4r基因敲除青鳉的生长与青春期发育情况，本研究发现Mc4r的缺失并不会改变青春期启动时间，但会显著延迟孵化过程。与野生型个体相比，基因敲除青鳉的胚胎发育进程存在迟缓现象。综上，青鳉体内的Mc4r信号通路参与生长调控，而非青春期启动的调控。