Genome-wide characterization of histone gene family in Pacific oyster ( Crassostrea gigas) ) and expression analysis under environmental stresses

Histones, the basic units of chromatin forming complexes with DNA, play crucial roles in the structure and composition of eukaryotic DNA. However, systematic analysis of the Histone gene family in molluscs is rarely studied. In this research, a total of 31 CgHistone genes were identified in Pacific oyster ( Crassostrea gigas). ). Phylogenetic analysis revealed that these CgHistone genes exhibited significant conservation across both vertebrates and invertebrates. Furthermore, motif and gene structure analysis corroborated the high degree of conservation observed in these CgHistone genes. Analysis of cis-acting elements within CgHistone genes has revealed that they play a pivotal role in regulating the expression of a diverse array of genes, thereby exerting a direct influence on growth, development, and immune responses. Meanwhile, expression profile analysis showed that most CgHistone genes were highest expressed in either female or male gonads, and had higher expression levels in the RM (rotary movement) to FS (free-swimming) stages of early development. More importantly, higher expression levels of CgHistone2/10/13/14/18/21 and lower expression levels of CgHistone24/25/26/29 under different environmental stresses suggest they may play crucial roles in abiotic stress. In summary, this study provides a comprehensive identification and analysis of the Histone gene family in Pacific oyster, laying the foundation for facilitating research on their function in response to environmental stresses.