The insulin-like growth factor 2 gene and locus in nonmammalian vertebrates: Organizational simplicity with duplication but limited divergence in fish.

The small, secreted peptide, insulin-like growth factor 2 (IGF2), is essential for fetal and prenatal growth in humans and other mammals. Human and mouse genes are located within a conserved linkage group and are regulated by parental imprinting, with / being expressed from the paternally derived chromosome, and from the maternal chromosome. Here, data retrieved from genomic and gene expression repositories were used to examine the gene and locus in 8 terrestrial vertebrates, 11 ray-finned fish, and 1 lobe-finned fish representing >500 million years of evolutionary diversification. The analysis revealed that vertebrate genes are simpler than their mammalian counterparts, having fewer exons and lacking multiple gene promoters. genes are conserved among these species, especially in protein-coding regions, and IGF2 proteins also are conserved, although less so in fish than in terrestrial vertebrates. The locus in terrestrial vertebrates shares additional genes with its mammalian counterparts, including tyrosine hydroxylase (), insulin (), mitochondrial ribosomal protein L23 (), and troponin T3, fast skeletal type (), and both and are present in the locus in fish. Taken together, these observations support the idea that a recognizable was present in the earliest vertebrate ancestors, but that other features developed and diversified in the gene and locus with speciation, especially in mammals. This study also highlights the need for correcting inaccuracies in genome databases to maximize our ability to accurately assess contributions of individual genes and multigene families toward evolution, physiology, and disease.