Molecular Mechanisms Of Maintaining Healthy Reproduction In Abdominal Teste

Studies have found that there are differences in the testicular and scrotal states of mammals.For example,the testes of some animals,such as whales,manatees,and elephants,remain in the abdominal cavity,while the testes of most mammals,including humans,are located in the extracorporeal scrotum.In this research paper,the former group of animals is called intraperitoneal testicular animals,and the latter one is scrotal testicular animals.In response to this phenomenon,many hypotheses have been proposed.Among them,the cooling hypothesis is the most classic and generally accepted one,which suggests that the scrotum provides a low temperature environment(2-4 °C lower than body’s core temperature)for normal spermatogenesis in the testis.Former studies have confirmed that elevated testicular temperature in mammals with extracorporeal scrotum can lead to abnormal spermatogenesis,such as decreased sperm count,decreased sperm motility,and increased proportion of sperm with abnormal morphology.It is noting that if the testes failed to descend in human beings and domestic animals,the cryptorchidism occurs.The testicles of cryptorchid species are exposed to the environment of high temperature for a long time,which seriously interrupts spermatogenesis.For abdominal testicular animals,although their testes remain in the abdominal cavity,they can still maintain normal spermatogenesis.So far,the molecular mechanism of reproductive adaptation in the animals of intra-abdominal testes remains unclear.Therefore,this study selected 16spermatogenesis-related genes(SPATA6,TCTE3,SEPT4,SEPT12,AKAP3,AKAP4,GAPDHS,CRISP2,AURKC,PICK1,DPY19L2,AR,KLHL10,TSSK4,HSPA2,and HSPA1L),and compared with the orthologous gene sequences of representative species to explore the following scientific questions: 1)Whether there are different selection pressures on the evolutionary lineage of mammals with different testicular phenotypes? 2)Is there molecular convergence among animals with abdominal testes?First,the site model,FEL model and REL model were used for selective pressure analysis,then positive selection were detected in seven genes(SPATA6,SEPT4,SEPT12,AKAP3,CRISP2,DPY19L2,and TSSK4),which suggest that these genes have undergone adaptive evolution during mammalian evolution.Next,the results from Branch model and the Branch-site model indicated that compared with scrotal-testis mammals,the spermatogenesis-related genes of the mammals with abdominal testis are subjected to stronger selection pressure.This indicates that spermatogenesis genes were subjected to adaptive evolution in the process of coping with the abdominal environment.Finally,the specific parallel/convergent amino acid substitution sites were found in 8 genes(SPATA6,TCTE3,SEPT4,AKAP3,CRISP2,DPY19L2,KLHL10,and HSPA1L)among animals with abdominal testes,showing that under similar intraperitoneal conditions,these animals have undergone molecular convergence in order to maintain normal spermatogenesis.In summary,through the evolutionary analysis of spermatogenesis-related genes,this study preliminarily revealed the genetic mechanism of normal spermatogenesis in animals with abdominal testicles,providing new information and evidence for the study of reproductive adaptation of male mammals.