SEQUENCES 5' OF THE HOMEOBOX OF THE HOX-1.4 GENE DIRECT TISSUE-SPECIFIC EXPRESSION OF LACZ DURING MOUSE DEVELOPMENT

The murine homeobox-containing gene Hox-1.4 is expressed in restricted patterns during embryogenesis and in male germ cells. To begin identi fication of the cis-acting elements regulating this expression, transg enic mice were generated carrying a chimeric construct that contained approx. 4 kb of 5' flanking sequence and approx. 1 kb of structural ge ne, fused in frame to the E. coli lacZ gene. This construct directed e xpression of the resulting Hox-1.4,beta-galactosidase fusion protein i n a pattern that reproduced virtually the complete embryonic and adult sites of expression of the endogenous gene. Embryonic expression of t he fusion protein was first detected in mesoderm at day 8.0 of gestati on (E 8.0). Between gestational ages E 8.5 to E 12.5, beta-gal express ion was observed in the somites, the lateral walls of the posterior my elencephalon, the dorsal region and ventral wall of the spinal cord, s pinal ganglia and pre-vertebrae and their surrounding mesenchyme, betw een presumptive ribs, as well as in mesenchymal layers in the lung, ki dney and portions of the gut. Expression was also noted in the pancrea s and in the supporting cells and sheath around subsets of peripheral nerves, sites that had not been detected previously. Adult expression was observed in testes, specifically in meiotic and post-meiotic male germ cells. In contrast, transgenic mice carrying 5' deletions of the construct which leave approx. 1.2 kb or approx. 2.0 kb of Hox-1.4 sequ ence 5' to the embryonic promoter, did not exhibit beta-gal staining. These deletion experiments defined at least one cis-acting control ele ment necessary for the expression of the Hox-1.4 gene to a 2 kb region located 2 to 4 kb 5' of the embryonic transcription start site.