Characterization of the chicken insulin receptor gene: Genomic organization and alternative promoter regulation

The insulin receptor (INSR) serves as a central mediator in insulin signaling pathway, critically regulating cellular growth, metabolism, and homeostasis. While extensively characterized in mammals, the genomic architecture and transcriptional regulation of the INSR in avian species remain largely unexplored. Here, we delineated the chicken INSR gene using 5'/3' rapid amplification of cDNA ends (RACE) and RT-PCR, identifying three alternative first exons (exon 1A, 1B, and 1C) and their associated promoters. Dual-luciferase reporter assays demonstrated that each promoter exhibits distinct promoter activity and differential responsiveness to insulin and dexamethasone. Quantitative RT-PCR analysis further revealed tissue-specific expression patterns of the resulting transcript isoforms, with significant differences observed between lean and fat broiler lines. MEME motif analysis revealed that INSR promoters exhibited differential motif architecture across the species examined and among the three alternative promoters of the chicken INSR gene. Our findings establish that INSR expression in chickens is regulated by three alternative promoters-a paradigm divergent from the mammalian model. This work provides fundamental insights into the evolutionary divergence of insulin signaling in birds and establishes a transcriptional framework for investigating insulin resistance mechanisms in avian species.