Abstract
The Chinese razor clam (Sinonovacula constricta), a bivalve species widely distributed in estuaries and mudflats, is often exposed to extreme environmental and microbial stresses. Histones are fundamental components of chromatin and play an important role in innate immunity, as demonstrated by its antimicrobial activities in clams. However, little attention has been paid to histones in bivalves. To fill this gap, we investigated the genomic distribution, structural characteristics, conserved motifs, and phylogenetic relationships of histones in S. constricta. A total of 114 histone genes were detected in the S. constricta genome, which were divided into 25 types in phylogenetic analysis. Among them, partial histones exhibited a tissue-dependent expression pattern, indicating that they may be involved in sustaining the homeostasis of organs/tissues in adult S. constricta. Furthermore, mRNA expression of certain histones changed significantly in S. constricta when infected with Vibrio parahaemolyticus, suggesting that histones play a role in the immune defense of S. constricta. All together, this study on histone genes in S. constricta not only greatly expands our knowledge of histone function in the clam, but also histone evolution in molluscs.
Highlights
Histones in eukaryotes are basically structural proteins of nucleosomes, which are responsible for the packing and compaction of DNA in the cell nucleus, thereby forming chromatin fiber [1,2,3]
Based on their structure and function, the histone gene family has been classified into two major groups: core histones comprised of H2A, H2B, H3, and
Canonical histones have a particular stem-loop structure located at the 30 untranslated region, which is generated by cleavage using a machinery involving U7 snRNP and protein factors such as the stem-loop binding protein (SLBP), as identified in both metazoans and protozoans [12]
Summary
Histones in eukaryotes are basically structural proteins of nucleosomes, which are responsible for the packing and compaction of DNA in the cell nucleus, thereby forming chromatin fiber [1,2,3]. Based on their structure and function, the histone gene family has been classified into two major groups: core histones comprised of H2A, H2B, H3, and. Histone genes with high copy numbers are structured into clusters These genes contain no introns and lack polyadenylation in their corresponding mRNAs, but contain a unique 30 end structure. The histone variant genes contain introns that allow for alternative splicing in some cases at least, and are not clustered in the genome [2,17]
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