Evolution of retinoic acid-dependent developmental regulatory system in chordates

我们证明维甲酸激活了海鞘胚胎中Hox1基因的表达。我们还发现维甲酸和Hox1对海鞘幼虫的器官发生有促进作用。尽管是海鞘类的近亲，但其幼虫基因组中不含视黄酸合成酶和视黄酸受体。我们在本研究中发现，幼鱼和海鞘都有不依赖视黄酸的机制来激活Hox1的转录。我们假设，幼虫和海鞘的共同祖先同时具有视黄酸依赖性和独立的Hox1激活途径。幼虫被认为在失去维甲酸相关基因的情况下存活了下来，可能是因为它们有两条多余的通路。

We demonstrated that retinoic acid activates expression of the Hox1 gene in ascidian embryos. We also showed that retinoic acid and Hox1 contributed to organogenesis of ascidian larvae. The larvacean Oikopleura dioica does not have retinoic acid synthase and retinoic acid receptor in their genome, even though it is a close relative of ascidians. We found in the present study that both larvaceans and ascidians have retinoic acid-independent mechanism to activate transcription of Hox1. We hypothesized that the common ancestor of larvaceans and ascidians had both retinoic acid-dependent and independent pathways for the Hox1 activation. Larvaceans are thought to have survived the loss of retinoic acid-related genes, probably because they had two redundant pathways.