Figure 5

Proposed somatostatin receptor evolutionary scheme. Numbers denote chromosome or linkage group assignments of SSTR genes in mapped genomes. Some of the SSTR genes have not been mapped to chromosomes or linkage groups, which is indicated by asterisks. Evolutionary scheme: Two ancestral vertebrate SSTR genes located on two different chromosomes duplicated in 2R, generating the vertebrate SSTR gene repertoire of SSTR1, -4 and -6, and SSTR2, -3 and -5 respectively. SSTR6 was lost from the lobe-finned fish lineage some time after the divergence of the coelacanth, and SSTR4 was lost from the ray-finned fish lineage some time before the divergence of the spotted gar. Following chromosome fusions, the ancestral teleost SSTR2, -3 and -5 genes duplicated in 3R, while only one gene for each of SSTR1 or -6 genes were conserved in some teleost lineages. Subsequent chromosome rearrangements in teleost evolution moved SSTR genes to different chromosomes. Data from neighboring genes families are consistent with these chromosome rearrangements. Not all SSTR subtype genes could be identified in some teleost genomes (Table 1). This could be either due to genuine gene losses, or perhaps due to the incomplete nature of these genome databases.