Preliminary Exploration Of Hox Gene Family Structure And Expression Pattern In Mytilus Coruscus

Hox gene,as an important regulator of body axis development and other developmental processes,usually provides the necessary spatio-temporal expression patterns for the body.However,current studies of Hox in mollusks have shown that Hox gene expression varies significantly in different species.Collinearity exists during the development process in some mollusks,while some species are partially present or absent in the development process.Therefore,it is controversial whether the collinearity expression of Hox subcluster level is universal,and does not exist in a unified view.Based on this situation,we selected the Mytilus coruscus,mined the Hox gene sequences from genome data,and q PCR was used to obtain the Hox expression profiles of five developmental stages and six adult tissues.Structure analysis,phylogenetic analysis,and selective pressure analysis were performed to speculate on the possible causes and factors of subcluster collinearity.The results of the study are as followsWe identified 11 Hox sequences from genome data,and named as Hox1-5,Antp,Lox2,Lox4,Lox5,Post1,and Post2.Analysis of the basic features of the 11 Hox sequences revealed that the longest was Hox2,encoding 703 amino acids,and the shortest was Post2,encoding 190 amino acids.All 11 Hox sequences were hydrophilic proteins,which provided the primary structural basis for Hox functions.Motif structural analysis and sequence alignment analysis revealed that the homeodomain region was highly conserved,and there were deletion and mutation of YPWM regulatory factors in different species and Hox sequences.Such deletion or mutation was consistent in bivalves.In phylogenetic analysis,106 amino acid sequences identified in M.coruscus were used to construct the phylogenetic tree.The result showed that all sequences had a homeodomain conserved region,and the clustering results tended to four clusters,and the sequences in each cluster had similarities in motif structure,indicating their functional consistency.The Hox sequences of mollusk were used to construct a phylogenetic tree,it was found that the clustering results were more tend to be 10 or 11,indicating that the Hox gene in mollusk had genealogy-specific functions.The result of Hox collinearity analysis in five bivalvia species and two gastropoda species found that M.coruscus and Mizuhopecten yessoensis had a complete Hox gene cluster,and in the other three species,deletion of Antp gene and absence of Hox collinearity was found,so we speculated a complete Hox cluster is an important prerequisite for Hox collinearity.The result of selection pressure analysis showed that Hox1,Hox4,Lox4,Post1,and Post2 have been subjected to a high level of purifying pressure,and Hox1,Hox4,and Post2 were overlapped with the leading gene in subcluster collinearity.Therefore,we speculated that the function of Hox gene subjected to purification selection pressure becomes important and conservative in evolution,thus becoming the leading gene.Hox expression profile data at five developmental stages indicated that M.coruscus had collinearity in the subcluster,and this proves before speculation: that a complete Hox gene cluster is an important prerequisite for the collinearity of Hox expression.Compared to M.yessoensis,the Hox3 gene was significantly expressed in the D-veliger larvae of M.coruscus.It also proved the hypothesis that changes in YPWM regulatory factors may lead to changes in Hox expression efficiency,thus providing a basis for the diversity of mollusks.Post2,Hox1,Hox4,and Post1 were highly expressed during the trochophore larvae and may relate to the formation of primary shells.The high expression of Hox3 in D-veliger larvae may be related to foot formation.The expression of Hox5 in the late stage may be related to benthic life.Lox2,4,and 5 are involved in neurogenesis,while Hox1 and Post1 are involved in shell formation.The Hox expression profile observed in six adult tissues showed that the expression levels of Lox2,Lox4,and Lox5 in gill tissues were much higher than other genes,and keep at the same level.This may be related to the higher metabolic rate of gill tissue.The high expression of Hox4 in gonads may be related to gonad development in M.coruscus.One or more Hox gene subclusters were expressed in different tissues,and the expression of the leading gene in the subclusters was often higher than other genes,indicating that there was a certain reservation in the collinear expression of Hox subclusters in adult tissues.The results of this study support the existence of Hox subcluster collinearity,and speculated on the formation mechanism of subcluster collinearity.It provides a new insight into the colinear expression of Hox and the diversity of mollusca,and it also has important theoretical significance for M.coruscus breeding.