| Summary: | <p>Abstract</p> <p>Background</p> <p>The pregnancy-specific glycoprotein (<it>Psg</it>) genes encode proteins of unknown function, and are members of the carcinoembryonic antigen (<it>Cea</it>) gene family, which is a member of the immunoglobulin gene (<it>Ig</it>) superfamily. In rodents and primates, but not in artiodactyls (even-toed ungulates / hoofed mammals), there have been independent expansions of the <it>Psg </it>gene family, with all members expressed exclusively in placental trophoblast cells. For the mouse <it>Psg </it>genes, we sought to determine the genomic organisation of the locus, the expression profiles of the various family members, and the evolution of exon structure, to attempt to reconstruct the evolutionary history of this locus, and to determine whether expansion of the gene family has been driven by selection for increased gene dosage, or diversification of function.</p> <p>Results</p> <p>We collated the mouse <it>Psg </it>gene sequences currently in the public genome and expressed-sequence tag (EST) databases and used systematic BLAST searches to generate complete sequences for all known mouse <it>Psg </it>genes. We identified a novel family member, <it>Psg31</it>, which is similar to <it>Psg30 </it>but, uniquely amongst mouse <it>Psg </it>genes, has a duplicated N1 domain. We also identified a novel splice variant of <it>Psg16 </it>(<it>bCEA</it>). We show that <it>Psg24 </it>and <it>Psg30 </it>/ <it>Psg31 </it>have independently undergone expansion of N-domain number. By mapping BAC, YAC and cosmid clones we described two clusters of <it>Psg </it>genes, which we linked and oriented using fluorescent <it>in situ </it>hybridisation (FISH). Comparison of our <it>Psg </it>locus map with the public mouse genome database indicates good agreement in overall structure and further elucidates gene order. Expression levels of <it>Psg </it>genes in placentas of different developmental stages revealed dramatic differences in the developmental expression profile of individual family members.</p> <p>Conclusion</p> <p>We have combined existing information, and provide new information concerning the evolution of mouse <it>Psg </it>exon organization, the mouse <it>Psg </it>genomic locus structure, and the expression patterns of individual <it>Psg </it>genes. This information will facilitate functional studies of this complex gene family.</p>
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