Evidence for Extensive Duplication and Subfunctionalization of in Armadillo ().

The control of infections by the vertebrate adaptive immune system requires careful modulation to optimize defense and minimize harm to the host. The Fc receptor-like () genes encode immunoregulatory molecules homologous to the receptors for the Fc portion of immunoglobulin (FCR). To date, nine different genes (, , and ) have been identified in mammalian organisms. is located at a separate chromosomal position from the locus, has conserved synteny in mammals and is situated between the and genes. Here, we show that this three gene block underwent repeated duplication in (nine-banded armadillo) resulting in six copies, of which five appear functional. Among 21 mammalian genomes analyzed, this expansion was unique to . Ig-like domains that derive from the five clustered functional gene copies show high structural conservation and sequence identity. However, the presence of multiple non-synonymous amino acid changes that would diversify individual receptor function has led to the hypothesis that endured subfunctionalization during evolution in . Interestingly, is noteworthy for its natural resistance to the pathogen that causes leprosy. Because is chiefly expressed by cytotoxic T and NK cells, which are important in cellular defense responses against , we speculate that subfunctionalization could be relevant for the adaptation of to leprosy. These findings highlight the species-specific diversification of family members and the genetic complexity underlying evolving multigene families critical for modulating adaptive immune protection.