THE HUMAN HOMEOBOX GENES MSX-1, MSX-2, AND MOX-1 ARE DIFFERENTIALLY EXPRESSED IN THE DERMIS AND EPIDERMIS IN FETAL AND ADULT SKIN

In order to identify homeobox genes which may regulate skin developmen t and possibly mediate scarless fetal wound healing we have screened a mplified human fetal skin cDNAs by polymerase chain reaction (PCR) usi ng degenerate oligonucleotide primers designed against highly conserve d regions within the homeobox. We identified three non-HOX homeobox ge nes, MSX-1, MSX-2, and MOX-1, which were differentially expressed in f etal and adult human skin. MSX-1 and MSX-2 were detected in the epider mis, hair follicles, and fibroblasts of the developing fetal skin by i n situ hybridization. In contrast, MSX-1 and MSX-2 expression in adult skin was confined to epithelially derived structures. Immunohistochem ical analysis of these two genes suggested that their respective homeo proteins may be differentially regulated. While Msx-1 was detected in the cell nucleus of both fetal and adult skin; Msx-2 was detected as a diffuse cytoplasmic signal in fetal epidermis and portions of the hai r follicle and dermis, but was localized to the nucleus in adult epide rmis. MOX-1 was expressed in a pattern similar to MSX early in gestati on but then was restricted exclusively to follicular cells in the inne rmost layer of the outer root sheath by 21 weeks of development. Furth ermore, MOX-1 expression was completely absent in adult cutaneous tiss ue. These data imply that each of these homeobox genes plays a specifi c role in skin development.