Identification Of The Olfactory Receptor Gene Family In Yellow River Carp （Cyprinus Carpio） And Its Expression Analysis At Embryonic Developmental Stages

The second whole-genome duplication occurred before the divergence of the lamprey fish from the jawed vertebrates,followed by a third whole-genome duplication in the teleosts.This WGD occurred about320 million years ago and is thought to be a WGD event unique to bony fishes.WGD has increased the diversity of gene numbers and provided a rich source of raw material for evolution.Following these wholegenome duplication events,specific genome duplication and polyploidy occurred in some branches of bony fishes,like common carp and goldfish in Cyprinidae.Multiple whole-genome duplications have occurred in Cyprinidae fishes,and the WGD experienced by common carp occurred in its common ancestor with goldfish,making it a good material for studying the mechanism of polyploid formation and the evolution of polyploid species.Also,common carp is a major aquaculture fish in China and worldwide,and is both important in aquaculture and genomic evolution.As a basic sense,the olfactory system is involved in feeding,courtship,socialization and avoidance of harm.The olfactory system mainly relies on nerves to transmit information.In the early stage of embryonic development,the nervous system starts to develop and the olfactory system can already function partially when the development of the olfactory system is not fully completed.Therefore,the early development of the olfactory system can be observed in the embryonic stage.In this study,we identified four types of olfactory genes in allotetraploid common carp（Cyprinus carpio）.A total of 49 OR genes and 6 TAAR genes were identified,which were distributed in clusters on common carp genome.The ORA gene family included 7 genes,ORA1 and ORA2,ORA3 and ORA4,ORA5 and ORA6 formed gene pairs,respectively,and their relationships were closer with each other in the evolutionary tree.the Olf C gene family included 7 genes.In zebrafish,Olf C genes are mainly distributed on chromosome 17 and 18,and in puffer fish,these genes are all distributed on chromosome 16 in cluster.In common carp,Olf C genes were mostly distributed on chromosomes A18 and B18,and were also distributed in clusters.Selection pressure analysis of all olfactory genes revealed that all genes were subjected to a relaxation in selection.Transcriptomic studies were performed on embryos at different developmental stages to initially explore the development of the olfactory system in the embryo.The transcriptomic data were filtered and it was found that the percent of clean reads in most of the sequencing data reached over 97% and the mapping rate reached over 90%,indicating the reliability of the sequencing data.Meanwhile,it was found that as the embryos developed,the expression of olfactory genes has increased after neurula compared to stages before neurula.