Evolution of retinoic acid-dependent developmental regulatory system in chordates

我们证明了维甲酸能激活Hox1基因在腹水胚胎中的表达。我们还发现维甲酸和Hox1参与了海鞘幼虫的器官发生。海鞘幼虫虽然是海鞘动物的近亲，但基因组中没有维甲酸合成酶和维甲酸受体。我们在目前的研究中发现，幼虫和海鞘动物都有维甲酸不依赖的机制来激活Hox1的转录。我们推测，幼虫和海鞘动物的共同祖先都有维甲酸依赖和独立的Hox1激活途径。幼虫被认为是在维甲酸相关基因丢失后幸存下来的，可能是因为它们有两条多余的路径。

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.