3种典型贝壳形成基因在红条毛肤石鳖早中期担轮幼虫中的表达特征OA北大核心

Polyplacophora mollusks(chitons)possess eight shell plates arranged serially along the anteri-or-posterior axis,distinct from other mollusks.From an evolutionary perspective,chitons,whose ancestors di-verged from Conchifera,such as clams and sea snails,at an early stage of evolution,are a group of Aculifera,rep-resenting a separate branch.Research on chiton shells is of great significance for understanding the origin and evo-lution of molluscan shells.In the present study,we screened four genes previously proven to be involved in con-chiferan shell development from the chiton Acanthochitona rubrolineata—including two tyrosinase genes,the sig-naling molecule bmp2/4 gene,and the transcription factor gata2/3 gene(designated as AR-tyr1,AR-tyr2,AR-bmp2/4,and AR-gata2/3,respectively)—and analyzed the correlation between their expression and shell development.We first predicted the conserved domains encoded by these genes and constructed phylogenetic trees.The four genes were identified as the orthologs of tyrosinase,bmp2/4,and gata2/3,and the encoded peptides were predicted to contain conserved domains typically observed in the encoded proteins.We then performed whole mount in situ hy-bridization to analyze their expression patterns in the key stages of early shell development(24,36,and 48 hpf).Slightly differing expression patterns of AR-tyr1 and AR-tyr2 were detected on the apical and ventral sides,as well as in the prototroch of larvae.AR-bmp2/4 was expressed in the apical and ventral sides,the prototroch,and the dorsal mesoderm of the larvae.These three genes were not conspicuously expressed in the shell field,contrary to their orthologs,a characteristically expressed in the shell fields of other conchiferans.In contrast,AR-gata2/3 was expressed in most shell field cells.Although associated with shell formation,the expression pattern of AR-gata2/3 varied markedly from that of its homologs in other conchiferans,whose expression is confined to the shell field edge.The dramatically different expression patterns of these vital shell-formation-associated genes between chitons and other conchiferans suggest considerable variations in the early shell development mechanisms in Aculifera and Conchifera.These findings enable further understanding of the relationship between molluscan shells and evolution.