Comparative Mammalian Genomics and Adaptive Evolution: Divergent Homologs and Novel Genes in the Cattle Genome

The convergence of two major currents in biology, comparative genomics and evolutionary biology, provides the pretext for greater understanding of the molecular mechanisms of adaptive evolutionary change. Our hypothesis is that rapidly evolving and novel genes contribute to the broad range of adaptive phenotypes observed among the mammalian orders. We have implemented an efficient scheme for the identification and characterization of divergent homologs and novel mammalian genes in order to obtain the necessary resources to test this hypothesis. The scheme is applicable to any species, particularly those whose genomes have not been completely sequenced. Herein, we discuss Bos taurus (domesticated cattle) as a model organism for studies in evolutionary biology and present a summary of results obtained using our scheme that led to the discovery of the MHCLA genes, a rapidly evolving gene family in cattle that is related to human ULBP/R4ET1. The rapid evolution of these genes appears to be related to their function as ligands for receptors present on natural killer cells of the immune system. In addition to MHCLA, 13 divergent homologs and 257 novel transcripts have been identified and are currently being characterized in detail for their chromosome map location and expression profiles in different tissues. The essential question to be answered is what roles these genes play in generating the adaptive phenotypes that arose among the Ruminantia during the past 85 million years.