Department of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, New York.
Department of Genetics, Albert Einstein College of Medicine, Bronx, New York.
Genome Biol Evol. 2017 Aug 1;9(8):2075-2092. doi: 10.1093/gbe/evx153.
The birth of novel genes, including their cell-specific transcriptional control, is a major source of evolutionary innovation. The lens-preferred proteins, crystallins (vertebrates: α- and β/γ-crystallins), provide a gateway to study eye evolution. Diversity of crystallins was thought to originate from convergent evolution through multiple, independent formation of Pax6/PaxB-binding sites within the promoters of genes able to act as crystallins. Here, we propose that αB-crystallin arose from a duplication of small heat shock protein (Hspb1-like) gene accompanied by Pax6-site and heat shock element (HSE) formation, followed by another duplication to generate the αA-crystallin gene in which HSE was converted into another Pax6-binding site. The founding β/γ-crystallin gene arose from the ancestral Hspb1-like gene promoter inserted into a Ca2+-binding protein coding region, early in the cephalochordate/tunicate lineage. Likewise, an ancestral aldehyde dehydrogenase (Aldh) gene, through multiple gene duplications, expanded into a multigene family, with specific genes expressed in invertebrate lenses (Ω-crystallin/Aldh1a9) and both vertebrate lenses (η-crystallin/Aldh1a7 and Aldh3a1) and corneas (Aldh3a1). Collectively, the present data reconstruct the evolution of diverse crystallin gene families.
新基因的诞生,包括其细胞特异性转录调控,是进化创新的主要来源。晶状体特异蛋白(脊椎动物:α-和β/γ-晶状体蛋白)为研究眼睛进化提供了一个切入点。晶状体蛋白的多样性被认为起源于趋同进化,通过在能够作为晶状体蛋白的基因启动子中多次独立形成 Pax6/PaxB 结合位点,从而产生了多样化的晶状体蛋白。在这里,我们提出αB-晶状体蛋白是由小热休克蛋白(Hspb1 样)基因的复制产生的,伴随着 Pax6 结合位点和热休克元件(HSE)的形成,随后又发生了另一次复制,产生了αA-晶状体蛋白基因,其中 HSE 被转化为另一个 Pax6 结合位点。β/γ-晶状体蛋白的起源基因是从祖先的 Hspb1 样基因启动子插入到钙结合蛋白编码区,在头索动物/被囊动物谱系的早期产生的。同样,一个祖先的醛脱氢酶(Aldh)基因通过多次基因复制,扩展成一个多基因家族,其中特定的基因在无脊椎动物晶状体(Ω-晶状体蛋白/Aldh1a9)和脊椎动物晶状体(η-晶状体蛋白/Aldh1a7 和 Aldh3a1)和角膜(Aldh3a1)中表达。总的来说,目前的数据重建了不同晶状体蛋白基因家族的进化。