MULTIPLE IG-LIKE FEATURING GENES DIVERGENT WITHIN AND AMONG INDIVIDUALS OF THE MARINE SPONGE GEODIA-CYDONIUM

The receptor tyrosine kinase of the marine sponge Geodia cydonium feat ures two extracellular Ig-like domains in which we recently documented RT-PCR polymorphism among individuals. Genomic-PCR analysis presented here revealed 14 unique sequences from four sponges, differing predom inantly in the sequence of an intron which splits the Ig-like domains. Nevertheless, analysis of putative coding regions in 19 distinct clon es (156 - 159 aa) from seven sponges revealed 69 positions of nucleoti de substitutions, 67.6 % of them non-synonymous, translating into 43 p ositions of divergent residues. Excluding aa deletions, these 19 seque nces share pairwise aa identities of 89 - 99 %. In three sponges, four or five unique Ig-like coding regions were scored. PCR amplification across this intron revealed multiple bands, polymorphic among five of six sponges. Further substantiated by Southern and Northern blots, it is evident that the genome of G. cydonium harbors multicopies of moder ately divergent Ig-like domains. Presently, this only appears parallel ed by the human KIR multigene family of NK cells MHC class I-specific receptors, which consist of two or three moderately divergent extracel lular Ig-like domains. (C) 1998 Elsevier Science B.V.