Transcription of H‐2 and Qa genes in embryonic and adult mice.

We have isolated cDNAs for three class I genes from an 8.5‐day C57Bl/6 mouse embryo cDNA library. Two of these cDNAs encode the classical transplantation antigens, H‐2Kb and H‐2Db. The third is a novelly spliced form of a Qa region gene, Q9, which lacks several exons including that encoding the transmembrane domain. Since this mRNA is detected on membrane‐bound polysomes it may encode a secreted protein. Transcripts for these three genes and the pseudo‐allele of Q9, Q7, were present at very low levels in the 8.5‐day and 14.5‐day embryo and in the 2‐day neonate, compared to most adult tissues. Q10, the liver‐specific secreted class I gene product in adults, is preferentially expressed in yolk sac and in fetal liver. We found no embryo‐specific class I gene expression.