The evolutionary origin of adaptive immune receptors is difficult to study below the phylogenetic level of the jawed vertebrates because PCR methods yield a high number of artefacts. In November 4 Nature Immunology, John Cannon and colleagues at the H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida, USA, show that a new strategy for selective cloning of cDNAs identifies diversified genes that contain immunoglobulin-like variable regions in a species lacking an adaptive immune response (Nature Immunology, doi:10.1038/ni849, November 4, 2002).

Cannon et al. developed a plasmid-based selection vector, that they termed Amptrap, and developed a cloning strategy using this vector that requires only minimal information about the gene of interest. They then analyzed DNA from amphioxus (Branchiostoma floridae) — a protochordate species that lacks an adaptive immune system — and identified multiple gene families having immunoglobulin-like variable (V) regions and which also possess...

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