Department of Biology, University of Maryland, College Park, MD, 20742, USA.
Cave Fish Development and Evolution Research Group, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, 650201, Yunnan, China.
Sci Rep. 2021 May 13;11(1):10312. doi: 10.1038/s41598-021-89702-6.
The direction of visceral organ asymmetry is highly conserved during vertebrate evolution with heart development biased to the left and pancreas and liver development restricted to opposing sides of the midline. Here we show that reversals in visceral organ asymmetry have evolved in Astyanax mexicanus, a teleost species with interfertile surface-dwelling (surface fish) and cave-dwelling (cavefish) forms. Visceral organ asymmetry is conventional in surface fish but some cavefish have evolved reversals in heart, liver, and pancreas development. Corresponding changes in the normally left-sided expression of the Nodal-Pitx2/Lefty signaling system are also present in the cavefish lateral plate mesoderm (LPM). The Nodal antagonists lefty1 (lft1) and lefty2 (lft2), which confine Nodal signaling to the left LPM, are expressed in most surface fish, however, lft2, but not lft1, expression is absent during somitogenesis of most cavefish. Despite this difference, multiple lines of evidence suggested that evolutionary changes in L-R patterning are controlled upstream of Nodal-Pitx2/Lefty signaling. Accordingly, reciprocal hybridization of cavefish and surface fish showed that modifications of heart asymmetry are present in hybrids derived from cavefish mothers but not from surface fish mothers. The results indicate that changes in visceral asymmetry during cavefish evolution are influenced by maternal genetic effects.
内脏器官不对称的方向在脊椎动物进化过程中高度保守，心脏发育偏向左侧，而胰腺和肝脏的发育则局限于中线的相对侧。在这里，我们展示了在墨西哥脂鲤（Astyanax mexicanus）中，内脏器官不对称的反转已经进化，这是一种具有可杂交的表栖（表栖鱼）和洞穴栖（洞穴鱼）形式的硬骨鱼。内脏器官不对称在表栖鱼中是常规的，但一些洞穴鱼的心脏、肝脏和胰腺发育发生了反转。在洞穴鱼侧线体节（LPM）中，正常左侧表达的 Nodal-Pitx2/Lefty 信号系统也存在相应的变化。Nodal 拮抗剂 lefty1（lft1）和 lefty2（lft2）将 Nodal 信号局限于左侧 LPM，它们在大多数表栖鱼中表达，但在大多数洞穴鱼的体节发生过程中，lft2 而不是 lft1 表达缺失。尽管存在这种差异，但多条证据表明，L-R 模式形成的进化变化受 Nodal-Pitx2/Lefty 信号的上游控制。因此，洞穴鱼和表栖鱼的正反交杂交表明，心脏不对称的修饰存在于来自洞穴鱼母亲的杂种中，但不存在于来自表栖鱼母亲的杂种中。结果表明，在洞穴鱼进化过程中内脏不对称的变化受母系遗传效应的影响。
