Based On The Analysis Of RNASE1 And AMY Gene Families, We Explore The Relevant Mechanisms Of Cetaceans' Eating Habits

Cetaceans are special types of the mammals returned to the ocean from the land about 50 million years ago.Cetaceans still maintain the characteristics of mammals,such as viviparous,breastfeeding,constant temperature and so on.The secondary aquatic adaptation brings a great challenge to the life of the cetaceans.In order to adapt to changes in the living environment,cetaceans motor,auditory sense,holding on body temperature,immune and feeding habits,etc.all made adaptive changes during the long evolutionary process.Paleontology and modern molecular biology evidence show that cetaceans evolved from terrestrial cloven-hoofed animals.The feeding habits of the terrestrial ancestors of the whales and the raw animals are all herbivorous,and the feeding habits of the whales are carnivorous.Cetaceans from terrestrial to aquatic process accompanied by food from the herbivorous to meat changes,but there are few researches on the molecular mechanism of whale dietary switch.In view of this,the pancreatic ribonuclease gene(RNASE1)family of cetaceans,which related to dietary switch,was investigated and compared to orthologous sequences from terrestrial mammals.We sorted out the RNASE1 genes of 43 mammals from 10 species containing seven cetaceans.Then,the phylogenetic relationship of RNASE1 gene family was constructed and the selective test was running,and we analyzed the change of RNasel amino acid sites between the cetaceans and ruminantia ancestral branches.Finally,calculated the isoelectric point(PI)of the RNasels between cetaceans and ruminantia.The results showed that there was only one RNASE1 sequence in the cetacean species,while the herbivorous Bovine and Camelidae had two or three.The results of the phylogenetic tree supported the independent replication of the RNASE1 gene in Cetartiodactyla.A positive selection was found in the Bovine and Camelidae,but not found in the whale end branches.Compared with the ancestral branch of ruminantia RNasel sequence,there were 12 amino acid changes in the ancestral branch of cetaceans' RNase1.The isoelectric point of the cetaceans' RNase1 is significantly higher than that of Bovine and Camelidae,which may relate to the dietary switch of cetaceans.Based on these,the enzymatic properties of RNase1 had been tested and found that the optimum pH range of RNase1 in the cetacean species was more alkaline.These studies revealed that the RNASE1 play an important role in feeding of cetaceans.In addition,we also studied the alpha-amylase gene(AMY)family.We sorted out the AMY genes of 37 mammals from 11 species containing seven cetaceans,The results showed that six mammals have AMY1 genes and AMY2 genes exist in all 37 mammals.There were one AMY2 sequence in the cetaceans,while the Bovine had two.Then,the phylogenetic relationship of AMY2 gene family was constructed and the selective test was running.The result of selective test supported that a positive selection was detected in Bovine but not in cetaceans.The AMY2 gene in cetaceans may also be associated with changes in feeding habits,but need further research.