Physiological Chemistry I, Biocenter, University of Wuerzburg, Am Hubland, D-97074 Wuerzburg, Germany.
Curr Biol. 2010 Oct 12;20(19):1729-34. doi: 10.1016/j.cub.2010.08.029. Epub 2010 Sep 30.
Polymorphisms in reproductive strategies are among the most extreme and complex in nature. A prominent example is male body size and the correlated reproductive strategies in some species of platyfish and swordtails of the genus Xiphophorus. This polymorphism is controlled by a single Mendelian locus (P) that determines the onset of sexual maturity of males. Because males cease growth after reaching puberty, this results in a marked size polymorphism. The different male size classes show pronounced behavioral differences (e.g., courtship versus sneak mating), and females prefer large over small males. We show that sequence polymorphisms of the melanocortin receptor 4 gene (mc4r) comprise both functional and non-signal-transducing versions and that variation in copy number of mc4r genes on the Y chromosome underlies the P locus polymorphism. Nonfunctional Y-linked mc4r copies in larger males act as dominant-negative mutations and delay the onset of puberty. Copy number variation, as a regulating mechanism, endows this system with extreme genetic flexibility that generates extreme variation in phenotype. Because Mc4r is critically involved in regulation of body weight and appetite, a novel link between the physiological system controlling energy balance and the regulation of reproduction becomes apparent.
生殖策略的多态性是自然界中最极端和最复杂的多态性之一。一个突出的例子是一些盘丽鱼属和剑尾鱼属鱼类的雄性体型和相关生殖策略。这种多态性由一个单一的孟德尔基因座（P）控制，决定了雄性的性成熟开始时间。由于雄性在达到青春期后停止生长，这导致了明显的体型多态性。不同的雄性体型表现出明显的行为差异（例如，求偶与偷偷交配），而雌性更喜欢大的雄性。我们表明，黑素皮质素受体 4 基因（mc4r）的序列多态性包括功能性和非信号转导两种形式，Y 染色体上的 mc4r 基因拷贝数的变化是 P 基因座多态性的基础。较大雄性中的非功能性 Y 连锁 mc4r 拷贝作为显性负突变，延迟了青春期的开始。作为一种调节机制的拷贝数变异赋予了这个系统极大的遗传灵活性，从而产生了表型的极端变异。由于 Mc4r 对体重和食欲的调节至关重要，因此控制能量平衡的生理系统与生殖调节之间出现了一种新的联系。
