CHANGING PATTERNS OF GAP JUNCTIONAL INTERCELLULAR COMMUNICATION AND CONNEXIN DISTRIBUTION IN MOUSE EPIDERMIS AND HAIR-FOLLICLES DURING EMBRYONIC-DEVELOPMENT

In the mouse embryo between embryonic days 12 (E12) and 16, regular ar rays of epidermal placodes on the mystacial pad develop into whisker f ollicles. This system was chosen for analysis of gap junctional interc ellular communication during differentiation. The patterns of communic ation were studied by microinjection of the tracers Lucifer yellow-CH (LY-CH) and neurobiotin (NB),while immunofluorescent staining was used to study distribution of connexins 26 and 43. Extensive communication was seen between keratinocytes in developing hair pegs or, in later-s tage hair follicles, in the germinative matrix. Coupling between adjac ent hair pegs via interfollicular epidermis was not observed. Coupling also became restricted as follicular cells differentiated to form out er root sheath, inner root sheath, and hair shaft. Extensive gap junct ional coupling is characteristic of keratinocytes that are rapidly pro liferating (as in hair pegs and germinative matrix). Follicular kerati nocytes commence differentiation shortly before restriction of gap jun ctional coupling becomes evident. Dermal mesenchymal cells undergoing different modes of differentiation also exhibit differences in gap jun ctional coupling, as evidenced by poor transfer of LY-CH between cells in dermal condensations of hair follicles compared with extensive tra nsfer elsewhere in the dermis. LY-CH and NB were not transferred betwe en epidermal or follicular epithelium and mesenchyme, arguing against a direct role for gap junctions permeable to known second messenger mo lecules or nucleotides in epithelial-mesenchymal interactions in this system. The distribution of connexins 26 and 43 in epidermis and hair follicles changed during differentiation but there was no correlation with changing patterns of dye transfer, indicating an unexpected degre e of complexity in the relationship between gap junctional intercellul ar communication and connexin protein distribution during development. (C) 1997 Wiley-Liss, Inc.