Abstract
BackgroundHatching is identified as one of the most important events in the reproduction of oviparous vertebrates. The genes for hatching enzymes, which are vital in the hatching process, are conserved among vertebrates. However, especially in teleost, it is difficult to trace their molecular evolution in detail due to the presence of other C6astacins, which are the subfamily to which the genes for hatching enzymes belong and are highly diverged. In particular, the hatching enzyme genes are diversified with frequent genome translocations due to retrocopy.ResultsIn this study, we took advantage of the rapid expansion of whole-genome data in recent years to examine the molecular evolutionary process of these genes in vertebrates. The phylogenetic analysis and the genomic synteny analysis revealed C6astacin genes other than the hatching enzyme genes, which was previously considered to be retained only in teleosts, was also retained in the genomes of basal ray-finned fishes, coelacanths, and cartilaginous fishes. These results suggest that the common ancestor of these genes can be traced back to at least the common ancestor of the Gnathostomata. Moreover, we also found that many of the C6astacin genes underwent multiple gene duplications during vertebrate evolution, and the results of gene expression analysis in frogs implied that genes derived from hatching enzyme genes underwent neo-functionalization.ConclusionsIn this study, we describe in detail the molecular evolution of the C6astacin gene in vertebrates, which has not been summarized previously. The results revealed the presence of the previously unknown C6astacin gene in the basal-lineage of jawed vertebrates and large-scale gene duplication of hatching enzyme genes in amphibians. The comprehensive investigation reported in this study will be an important basis for studying the molecular evolution of the vertebrate C6astacin genes, hatching enzyme, and its paralogous genes and for identifying these genes without the need for gene expression and functional analysis.
Highlights
Hatching is identified as one of the most important events in the reproduction of oviparous vertebrates
Identification of newly cloned C6ast genes in basal lineage fishes We conducted a comprehensive search of the genome databases (Additional file 2: Table S1) and identified each relevant gene
We could not find any traces of C6ast gene pair derived from teleost specific whole-genome duplication (WGD). These results suggested that the multiple copies of C6ast genes in teleostei were derived from a single C6ast gene
Summary
Hatching is identified as one of the most important events in the reproduction of oviparous vertebrates. The genes for hatching enzymes, which are vital in the hatching process, are conserved among vertebrates. Especially in teleost, it is difficult to trace their molecular evolution in detail due to the presence of other C6astacins, which are the subfamily to which the genes for hatching enzymes belong and are highly diverged. During the evolution of teleosts, the C6ast genes have been duplicated, and they are classified into the subfamily, which contains the C6astacin4/5 (C6ast4/5), nephrosin (npsn), patristacin (pastn), pactacin (pac), and HEs [9]. The functions and expression patterns of these subfamily genes have diverged. While the functions of other C6ast are diverse, the functions of teleost HEs are limited, since these genes are only expressed in hatching gland cells in pre-hatched embryos [1, 2]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
