Expression of homologous homeo-box-containing genes in differentiated human teratocarcinoma cells and mouse embryos

Human chromosome 17 contains a cluster of at least three distinct homeo box regions, Hu1, Hu2, and Hu5, within a 20 kb stretch of DNA. A mouse homeo box region, Mu1, which maps to chromosome 11, was isolated and found to contain extensive nucleotide homology with a 4 kb region encompassing the Hu1 homeo box. The conservation of these chromosomal regions between man and mouse was confirmed by nucleotide sequence analysis: approximately 380 bp of DNA are more than 90% homologous and the 61 amino acids of the homeo box domain are perfectly conserved. We found that a human teratocarcinoma cell line expresses high levels of Hu1 homeo-box-containing mRNA only after differentiation of the cells following treatment with retinoic acid. In contrast, mouse teratocarcinoma cells did not express Mu1 homeo-box-containing mRNA at any stage of differentiation, whereas the expression of such transcripts was detected in mouse embryos from 10 to 17 days of gestation.