Garstang Myles G, Ferrier David E K
The Scottish Oceans Institute, Gatty Marine Laboratory, University of St Andrews, East Sands, St Andrews, Fife, KY16 8LB, UK.
School of Biological Sciences, University of Essex, Wivenhoe, Colchester, Essex, CO4 3SQ, UK.
Dev Genes Evol. 2018 Jan;228(1):13-30. doi: 10.1007/s00427-017-0600-9. Epub 2018 Jan 2.
Retrogenes are formed when an mRNA is reverse-transcribed and reinserted into the genome in a location unrelated to the original locus. If this retrocopy inserts into a transcriptionally favourable locus and is able to carry out its original function, it can, in rare cases, lead to retrogene replacement. This involves the original, often multi-exonic, parental copy being lost whilst the newer single-exon retrogene copy 'replaces' the role of the ancestral parent gene. One example of this is amphioxus SYCP1, a gene that encodes a protein used in synaptonemal complex formation during meiosis and which offers the opportunity to examine how a retrogene evolves after the retrogene replacement event. SYCP1 genes exist as large multi-exonic genes in most animals. AmphiSYCP1, however, contains a single coding exon of ~ 3200 bp and has inserted next to the ParaHox cluster of amphioxus, whilst the multi-exonic ancestral parental copy has been lost. Here, we show that AmphiSYCP1 has not only replaced its parental copy, but also has evolved additional regulatory function by co-opting a bidirectional promoter from the nearby AmphiCHIC gene. AmphiSYCP1 has also evolved a de novo, multi-exonic 5'untranslated region that displays distinct regulatory states, in the form of two different isoforms, and has evolved novel expression patterns during amphioxus embryogenesis in addition to its ancestral role in meiosis. The absence of ParaHox-like expression of AmphiSYCP1, despite its proximity to the ParaHox cluster, also suggests that this gene is not influenced by any potential pan-cluster regulatory mechanisms, which are seemingly restricted to only the ParaHox genes themselves.
反转录基因是在mRNA被反转录并重新插入到基因组中一个与原始基因座无关的位置时形成的。如果这个反转录拷贝插入到一个转录有利的基因座并且能够执行其原始功能，那么在极少数情况下，它会导致反转录基因替代。这涉及到原始的、通常是多外显子的亲本拷贝丢失，而较新的单外显子反转录基因拷贝“取代”了祖先亲本基因的作用。一个例子是文昌鱼的SYCP1，该基因编码一种在减数分裂期间用于联会复合体形成的蛋白质，它为研究反转录基因在反转录基因替代事件后如何进化提供了机会。SYCP1基因在大多数动物中以大型多外显子基因的形式存在。然而，文昌鱼的AmphiSYCP1包含一个约3200bp的单一编码外显子，并插入到文昌鱼的副同源盒基因簇附近，而多外显子的祖先亲本拷贝已经丢失。在这里，我们表明，AmphiSYCP1不仅取代了其亲本拷贝，还通过从附近的AmphiCHIC基因中借用一个双向启动子进化出了额外的调控功能。AmphiSYCP1还进化出了一个全新的、多外显子的5'非翻译区，该区域以两种不同的异构体形式表现出不同的调控状态，并且除了在减数分裂中的祖先作用外，在文昌鱼胚胎发育过程中还进化出了新的表达模式。尽管AmphiSYCP1靠近副同源盒基因簇，但它没有副同源盒样的表达，这也表明该基因不受任何潜在的全簇调控机制的影响，这些机制似乎只限于副同源盒基因本身。
