Sea urchins are sophisticated invertebrates whose biology holds many clues to the evolution of the vertebrates. These organisms very effectively remove any invading bacterial pathogens and other foreign material from within their coeloms by means of a range of macrophage-like cells. It seems that sea urchins have a simplified version of the complement system that can mediate opsonization of pathogens. Nair et al. have been investigating the immune responses of sea urchins by analysis of expressed sequence tags generated from coelomocytes and discovered that a wide range of genes are up-regulated in response to bacterial lipopolysaccharide. What was particularly interesting was a previously unknown gene family that represented 60% of the ESTs and could undergo alternative splicing to yield around 15 translatable elements. The evidence suggested that these were immune response proteins under positive selection for diversification, and revealed a greater level of complexity of putative responses than anticipated for an invertebrate group. -- CA
Physiol. Genomics 22, 33 (2005)
