Towards a molecular code for individuality in the absence of MHC: screening for individually variable genes in the urochordate Ciona intestinalis

Urochordates possess several well described allorecognitions systems, the molecular nature of those is not yet understood. A prerequisite for any self-/nonself discimination system is the presence of a group of highly variable molecules, which should vary between individuals. Using suppression subtractive hybridisation (SSH) we surveyed Ciona intestinalis for individually variable genes. Our search so far identified two genes, ciS7 and ciMETA2, which both display an unexpected high degree of intra- and interindividual variability, code for secreted proteins, and contain multiple domains suitable for protein-protein interactions. The possible role of these molecules in allorecognition is discussed.