DIFFERENTIAL EXPRESSION OF 2 DIFFERENT HOMEOBOX GENE FAMILIES DURING MOUSE TEGUMENT MORPHOGENESIS

The expression of six genes belonging to two different homeobox gene f amilies was studied during the embryonic and postnatal morphogenesis o f head and body regions of the mouse integument. The first family incl uded the Otx1 and Otx2 genes, both related to the orthodenticle Drosop hila gene and the second was represented by four members of the Antenn apedia class HOX genes: Hoxc8 and three Hoxd genes, d9, d11 and d13. I n situ hybridizations with S-35 labeled antisense RNA probes were perf ormed on head serial frontonasal sections, as well as entire embryo an d postnatal tail longitudinal sections. The expression of these genes shows a differential spatiotemporal pattern along the cephalo-caudal a xis. In 12.5-day and 15.5-day embryos, the Otx2 gene expression is res tricted to the nasal epithelium and its associated glands, while the O tx1 transcripts are present in both nasal and facial integuments, incl uding nasal glands and hair vibrissa follicles. The Hoxc8 expression f irst appears in skin at 14.5 days of gestation in the sternal region a nd is extended at 16.5 days to the thoracic ventral and lumbar dorsal regions. The Hoxd9 and Hoxd11 genes are only expressed in the caudal s kin from 14.5 days of gestation. The Hoxd13 transcripts are the last t o appear, 2 days after birth, and are limited to the last epidermal ce lls to differentiate, i.e. those of the hair matrix of the caudal pela ge hair follicles. Taken together, these observations strengthen the h ypothesis that different homeobox gene families specify the regional i dentity of the skin in the cephalic and body regions.