Gredler Marissa L, Sanger Thomas J, Cohn Martin J
Department of Biology, University of Florida, Gainsville, Fla, USA.
Sex Dev. 2015;9(1):21-33. doi: 10.1159/000363757. Epub 2014 Jun 20.
In most amniotes, the intromittent organ is a single phallus; however, squamates (lizards, snakes, and amphisbaenians) have paired hemiphalluses. All amniotes studied to date initiate external genital development with the formation of paired genital swellings. In mammals, archosaurs, and turtles, these swellings merge to form a single genital tubercle, the precursor of the penis and clitoris; however, in squamates, the paired genital buds remain separate, giving rise to the hemiphalluses (hemipenes in males and hemiclitores in females). Although the molecular genetics and sexual differentiation of the genital tubercle have been investigated in mammals and birds, little is known about hemiphallus development. Here we describe development of the cloaca and hemiphallus in the green anole, Anolis carolinensis. Each hemiphallus originates as a protuberance that emerges at the ventral base of the hindlimb bud. Development of the hemipenes resembles penis development; however, differences exist in their tissue composition, morphogenesis, and gene expression patterns. These findings reveal aspects of phallus development that appear to be evolutionarily labile, both within squamates and more broadly among reptiles, and identify features that are conserved across amniotes. Our results, together with parallel studies in other reptilian taxa, suggest potential mechanisms for the diversification of external genital form.
在大多数羊膜动物中，交配器官是单个阴茎；然而，有鳞目动物（蜥蜴、蛇和蚓蜥）具有成对的半阴茎。迄今为止，所有已研究的羊膜动物都是通过成对生殖隆起的形成来启动外生殖器发育的。在哺乳动物、主龙类和龟类中，这些隆起融合形成单个生殖结节，即阴茎和阴蒂的前身；然而，在有鳞目动物中，成对的生殖芽保持分离，发育为半阴茎（雄性为半阴茎，雌性为半阴蒂）。尽管已经对哺乳动物和鸟类的生殖结节的分子遗传学和性别分化进行了研究，但对于半阴茎的发育知之甚少。在这里，我们描述了绿安乐蜥（Anolis carolinensis）泄殖腔和半阴茎的发育过程。每个半阴茎起源于后肢芽腹侧基部出现的一个突起。半阴茎的发育类似于阴茎的发育；然而，它们在组织组成、形态发生和基因表达模式上存在差异。这些发现揭示了阴茎发育的一些方面，这些方面在有鳞目动物内部以及更广泛的爬行动物中似乎在进化上不稳定，并确定了在羊膜动物中保守的特征。我们的结果，连同对其他爬行动物类群的平行研究，提示了外生殖器形态多样化的潜在机制。
