Islet基因調節序列的演化與脊椎動物成對的鰭起源有關

Abstract

脊椎動物成對附肢的起源和演化是演化發育生物學中一個長久存在的問題。最近的化石證據發現有頷類祖先具有一個允許成對側鰭發育的「鰭潛能區」，而此區域在演化過程被局限演化出現存有頷類動物單基底的側肢。我試圖通過研究成對後肢發育過程的保守轉錄因子來了解鰭潛能區的分子組成。我針對有頷類演化支動物取樣，在不同物種的腹鰭中皆發現了Islet同源基因的保守表達，並確定了一個名為CR2的保守增強子可調控此基因表達。我同時證明在斑馬魚胚中過度表達isl1可在少數個體誘導出一個類似鰭的結構，此類鰭構造可表達數個鰭的標誌基因，這表明了isl1足以誘導鰭的發育。因此我假設祖先的「鰭潛能區」可能是由Islet同源基因所組成，並受到其增強子CR2的調控，而增強子序列的改變可能成為單基底鰭演化的基礎。

The origin and evolution of vertebrate paired appendages is a long-standing question in evolutionary developmental biology. Recent fossil discoveries indicate the presence of an ancestral “zone of fin competence” where paired lateral fins emerge, and the subsequent restriction of this zone led to a monobasal fin seen in extant gnathostomes. I sought to identify the molecular components of the zone of fin competence by examining the conserved factors in paired pelvic appendage development. I sampled the gnathostome clade, found a conserved expression of Islet orthologs in the pelvic fin, and identified a conserved enhancer CR2 driving such expression. I also show that overexpression of isl1 in zebrafish embryos induces outgrowth of a fin-like structure expressing several fin marker genes, suggesting the sufficiency of isl1 to initiate a fin program. I propose that the ancestral “zone of fin competence” is established by Islet genes, which are regulated by the enhancer CR2. Modification to the enhancer may underlie the evolution of monobasal fins.