A novel ortholog of serum response factor (SRF) with immune defense function identified in Crassostrea hongkongensis

Serum response factor (SRF) function is essential for transcriptional regulation of numerous growth-factor-inducible genes and triggers proliferation, differentiation and apoptosis of the cells. In this report, the first mollusk serum response factor like homolog gene (designated ChSRF) was identified and characterized from the Hong Kong oyster, Crassostrea hongkongensis. The full-length cDNA of ChSRF was 1716 bp in length and encodes a putative protein of 434 amino acids respectively, and shares the MADS domain at the N-terminal. ChSRF is ubiquitously expressed in various tissues, with the highest expression level observed in muscle. Temporal expression of ChSRF following microbe infection shows that the expression of ChSRF in hemocytes increases from 3 to 24 h post-challenge. As a target gene of SRF, β-actin demonstrates a similar gene expression mode in constitutive tissue and pathogen infection. Furthermore, some protein profiles of ChSRF was revealed, fluorescence microscopy results show that ChSRF located in the nuclei of HeLa cells and over-expression of ChSRF activated the transcriptional activities of MAPK signal pathway in HEK293T cells. These results indicate that ChSRF maybe play an important role in signal transduction in the immunity and development response of oysters. Furthermore, we found that ChSRF could regulate the expression of β-actin gene, which indicate that ChSRF is a muscle differentiation regulator in the oyster and it will help us to improve aquaculture production.