Gene Conversions in the Siglec and CEA Immunoglobulin Gene Families of Primates

Siglecs and CEA are two families of cell surface proteins belonging to the immunoglobulin superfamily. They are thought to be involved in cell-cell interactions and have various other biological functions. We used the GENECONV program that applies statistical tests to detect gene conversion events in each family of five primate species. For the Siglec family, we found that gene conversions are frequent between CD33rSiglec genes, but are absent between their conserved Siglec genes. For the CEA family, half of gene conversion events detected are located in coding regions. A significant positive correlation was found between the length of the conversions and the similarity of the converted regions only in the Siglec gene family. Moreover, we found an increase in GC-content and similarity in converted regions compared to non-converted regions of the two families. Furthermore, in the two families, gene conversions occur more frequently in the extracellular domains of proteins, and rarely in their transmembrane and cytoplasmic regions. Finally, these two families appear to be evolving neutrally or under negative selection