ABSTRACT: The Chinese surf clam (Mactra chinensis) is an economically important clam, distributed in Liaoning and Shandong province. In recently years，because of coastal environmental deterioration and overfishing, the natural population of M. chinensis have considerably declined . In this paper, we study the microRNA transcriptome of gills, including control and experimental group was sequenced through Illumina Hi-seq 2500 CE. And the differential expression was used to find the functional microRNA response to the Cd2+ exposure. Through Illumina Hi-seq 2500, a total of 14,415,256 clean reads and 15,570,111 clean reads were yielded in the gill of control and experimental group respectively. A total of 14,584,077 sRNA, in which there are 12,505,055 sRNA shared by S01 & S02, including 187,859 unique sRNA. The distribution of the sRNA length in the two library was similar, most of them were 26-27 nt. 27 nt was the most abundant length in S01, followded by 28 nt, 26 nt, and 23 nt; 26 nt was the most abundant length in S02, and followed by 27 nt, 28 nt and 23 nt. 50 miRNA was found in unique sRNA, including 38 conserved and 12 novel genes. The most abundant length of microRNA in the two library was the same, 23 nt. Through the analyze of differential expression analysis, the expression of 5 miRNA was induced with significantly difference, and 17 miRNA was down regulated and 28 miRNA was up regulated without significantly difference. So the miRNA in gill of M. chinensis might involve the environmental stress. 542 target genes were yielded when the 50 miRNA were hit to mRNA genome. And the target genes of differential expression miRNA were annotated by hitting to the NCBI database, and 4 genes hit to the COG, 1 genes hit to the GO, 5 genes hit to the KEGG and 11 genes hit to the nr database. The genes hit to the NCBI database include E3 ubiquitin-protein ligase, Wnt signaling pathway and Regulator of G-protein signaling 22.
