The dynamic genome: allelic variations in the genomes of single cells from an invertebrate metazoan (#8)
The diversification of immune receptor genes provides a powerful mechanism for the detection of a large array of non-self determinants. This strategy is best exemplified the immunoglobulin superfamily genes of the vertebrate adaptive immune system. Each circulating lymphocyte genome contains only one functional allele at the Ig/TCR locus, which is ‘constructed’ from a large array of gene segments. Although diversifying immune response gene families have been reported in some invertebrates, little is known about the nature of the molecular mechanisms that underpin such gene diversification. Previous work has demonstrated that sea urchins possess and express a wide repertoire of 185/333 genes in response to immunological challenge. Each individual may possess more than 100 alleles of this gene family in its genome. We report here on the manifestation of somatic gene diversity of the sea urchin 185/333 genes. This study investigated the diversity of 185/333 alleles in the genomes of individual blood cells. Fluorescence Activated Cell Sorting was used to collect individual blood cells into the wells of a multi-well plate. 185/333 sequences were then analysed using allele-specific primers. Our results showed that individual blood cells contained unique haplotypes of 185/333 alleles. This diversification was apparent in specific subpopulations of blood cells. Taken together, our data suggest that sea urchins somatically diversify their 185/333 gene repertoire. It also lends support to the notion that there may be different, but as yet undiscovered, flavours of somatic diversification amongst the metazoans.