Histone H4: Genomic identification and function analysis in pearl oyster Pinctada fucata martensii

Histone H4 together with histones H2A, H2B and H3 constitutes the nucleosome and is involved in DNA packaging and regulation of immune response. In this study, we identified 123 H4 genes from nine species by compressive genomic analysis, and H4 gene was contracted with only two members (designed as PmH4-1 and PmH4-2) in the genome of pearl oyster Pinctada fucata martensii. Evolution analysis showed that this contraction happened after the divergence of P. f. martensii and Crassostrea gigas. The full-length cDNA of PmH4-1 is 561 bp, including an open reading frame (ORF) of 312 bp, a 5 '-untranslated region (UTR) of 37 bp and a 3 '-UTR of 212 bp. The full-length cDNA of PmH4-2 is 556 bp, containing an ORF of 342 bp, a 5 '-UTR of 84 bp and a 3 '-UTR of 130 bp. Sequence analysis indicated that PmH4-1 was one canonical histone, and PmH4-2 was considered as a variant H4 that showed different structure and have only 55.34% identity with the canonical H4. Tissue expression pattern showed that PmH4-1 was highly expressed in the gonad, and PmH4-2 was mostly expressed in the mantle edge. After lipopolysaccharide stimulation, PmH4-2 was highly induced, and PmH4-1 was slightly upregulated without significance, indicating that PmH4-2 participates in the innate immune responses in pearl oyster P. f. martensii. These results lay the foundation for the study of the H4 family and provide theoretical support for understanding the immune defence mechanism of pearl oyster.

Automated summary

A comprehensive genomic analysis identified 123 H4 genes from nine species, with only two members in the genome of pearl oyster Pinctada fucata martensii. Evolution analysis revealed that this contraction occurred after the divergence of P. f. martensii and Crassostrea gigas. The two H4 genes showed differences in tissue expression patterns and immune responses.