Laboratory of Organ Morphogenesis, Department of Ecological Developmental Adaptability Life Sciences, Graduate School of Life Sciences, Tohoku University, Aobayama Aoba-ku, Sendai, 980-8578, Japan.
Laboratory of Molecular and Developmental Biology, National Institute of Genetics, Mishima, Shizuoka, 411-8540, Japan.
Sci Rep. 2022 May 7;12(1):7521. doi: 10.1038/s41598-022-11180-1.
The median fins of modern fish that show discrete forms (dorsal, anal, and caudal fins) are derived from a continuous fold-like structure, both in ontogeny and phylogeny. The median fin fold (MFF) hypothesis assumes that the median fins evolved by reducing some positions in the continuous fin fold of basal chordates, based on the classical morphological observation of developmental reduction in the larval fin folds of living fish. However, the developmental processes of median fins are still unclear at the cellular and molecular levels. Here, we describe the transition from the larval fin fold into the median fins in zebrafish at the cellular and molecular developmental level. We demonstrate that reduction does not play a role in the emergence of the dorsal fin primordium. Instead, the reduction occurs along with body growth after primordium formation, rather than through actively scrapping the non-fin forming region by inducing cell death. We also report that the emergence of specific mesenchymal cells and their proliferation promote dorsal fin primordium formation. Based on these results, we propose a revised hypothesis for median fin evolution in which the acquisition of de novo developmental mechanisms is a crucial evolutionary component of the discrete forms of median fins.
现代鱼类具有离散形式（背鳍、臀鳍和尾鳍）的中轴鳍由连续的褶状结构发育而来，无论是在个体发生还是系统发生中。中轴鳍褶（MFF）假说假设中轴鳍是通过减少基干脊索动物连续鳍褶中的某些位置进化而来的，这是基于对现存鱼类幼虫鳍褶发育性减少的经典形态学观察。然而，中轴鳍的发育过程在细胞和分子水平上仍不清楚。在这里，我们描述了在细胞和分子发育水平上斑马鱼幼虫鳍褶向中轴鳍的转变。我们证明，在背鳍原基出现过程中，减少并不起作用。相反，减少是在原基形成后与身体生长同时发生的，而不是通过诱导细胞死亡主动清除非鳍形成区域来实现的。我们还报告说，特定间充质细胞的出现及其增殖促进了背鳍原基的形成。基于这些结果，我们提出了一个修正的中轴鳍进化假说，其中获得新的发育机制是中轴鳍离散形式的一个关键进化组成部分。
