Characterization of the genomic and transcriptional structure of chicken NRG4 gene.

Neuregulin 4 (NRG4) is an important adipocytokine, which plays crucial roles in maintaining energy balance, regulating glucose and lipid metabolism, and preventing non-alcoholic fatty liver disease in mammals. At present, the genomic organization, transcript and protein isoforms of human NRG4 gene have been fully explored. Previous studies in our laboratory have shown that the NRG4 gene is expressed in chicken adipose tissue, but the chicken NRG4 (cNRG4) genomic structure, transcript and protein isoforms are still unknown. To this end, in this study, the genomic and transcriptional structure of the cNRG4 gene were systematically investigated using rapid amplification of cDNA ends (RACE) and reverse transcription-polymerase chain reaction (RT-PCR). The results showed that the coding region (CDS) of the cNRG4 gene was small, but it had a very complex transcriptional structure characterized by multiple transcription start sites, alternative splicing, intron retention, cryptic exons, and alternative polyadenylation, thus leading to production of four 5?UTR isoforms (cNRG4 A, cNRG4 B, cNRG4 C, and cNRG4 D) and six 3?UTR isoforms (cNRG4 a, cNRG4 b, cNRG4 c, cNRG4 d, cNRG4 e, and cNRG4 f) of the cNRG4 gene. The cNRG4 gene spanned 21,969 bp of genomic DNA (Chr.10:3,490,314~3,512,282) and consisted of 11 exons and 10 introns. Compared with the cNRG4 gene mRNA sequence (NM_001030544.4), two novel exons and one cryptic exon of the cNRG4 gene were identified in this study. Bioinformatics analysis, RT-PCR, cloning and sequencing analysis showed that the cNRG4 gene could encode three protein isoforms (cNRG4-1, cNRG4-2 and cNRG4-3). This study lays a foundation for further research on the function and regulation of the cNRG4 gene.