Genomic structure and immunological response of an STAT4 family member from rock bream (Oplegnathus fasciatus)

• Complete genomic structure of STAT4 from rock bream was identified.
• RbSTAT4 mRNA expression was detected in different tissues and was highly expressed in gills.
• Bacterial and viral infections caused significant regulation of RbSTAT4 gene expression.

The Janus tyrosine kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway plays a critical role in host defense against viral and bacterial infections. STAT proteins are a group of transcription factors that translocate into the nucleus and are critical for the induction of many genes crucial for the allergic cascade and immune defense. In the present study, a member of the STAT4 family was identified from rock bream (RbSTAT4) at the genomic level, and its transcriptional regulation in response to different pathological stimuli under in vivo conditions was investigated. The genomic sequence of RbSTAT4 is approximately 15.6 kb in length, including a putative core promoter region and 24 exons interrupted by 23 introns. Bioinformatics analysis of RbSTAT4 identified the presence of typical and conserved features of the STAT4 family, including the STAT_int domain, STAT alpha domain, STAT bind domain, linker domain, SH2 domain, and transcriptional activation domain. According to the phylogenetic analysis, RbSTAT4 exhibited the closest evolutionary proximity with the STAT4 member from mandarin fish (Siniperca chuatsi). The RbSTAT4 transcript in healthy rock breams was detected to have ubiquitous expression in 11 different tissues examined, where liver and spleen tissues showed moderate expressions compared with the highest expression level detected in gill tissue. The time-course in vivo immune stimulation of rock bream with lipopolysaccharide, poly I:C, live Edwardsiella tarda, and rock bream iridovirus caused significant transcriptional regulation of the RbSTAT4 expression in gill, head kidney, and spleen tissues, suggesting that RbSTAT4 is involved in immune regulation mechanisms and/or signaling cascades, orchestrating against both bacterial and viral pathogens.