Genomic organization of the IGF1, IGF2, MYF5, MYF6 and GRF/PACAP genes across Salmoninae genera.

Whole-genome duplication in the ancient ray-finned fish and subsequent tetraploidization in the ancestor to the salmonids have complicated genomic and candidate gene studies in these organisms as many genes with multiple copies are present throughout their genomes. In an attempt to identify genes with a potential influence on growth and development, we investigated the genomic positions of insulin-like growth factors 1 and 2 (IGF1, IGF2), myogenic factors 5 and 6 (MYF5, MYF6) and growth hormone-releasing factor/pituitary adenylate cyclase-activating polypeptide (GRF/PACAP) in three salmonid species: rainbow trout (Oncorhynchus mykiss), Atlantic salmon (Salmo salar) and Arctic charr (Salvelinus alpinus). Our results suggest a tight association between the IGF1, MYF5 and MYF6 genes in all three species. We further localized the duplicated copies of IGF1 to the homeologous linkage groups RT-7/15 in rainbow trout and AC-3/24 in Arctic charr, and the two copies of MYF6 to homeologous linkage groups AS-22/24 in Atlantic salmon. Localization of GRF/PACAP to RT-7, AS-31 and AC-27 and IGF2 to RT-27, AS-2 and AC-4 in rainbow trout, Atlantic salmon and Arctic charr respectively is consistent with previously reported homologies among these chromosomal segments identified using other genetic markers. However, localization of the second copy of GRF/PACAP to RT-19 and AC-14 and the duplicated copy of IGF2 to AC-19 suggest a possible new homology/homeology between these chromosomes. These results might also be an indication of a more ancient polyploidization event that occurred deep in the ray-finned fish lineage.