Multiple gap junction genes are utilized during rat skin and hair development

Abstract

The expression of four different gap junction gene products (α1, β1, β2, and β3) has been analysed during rat skin development and the hair growth cycle. Both α1 (Cx43) and β2 (Cx26) connexins were coexpressed in the undifferentiated epidermis. A specific, developmentally regulated elimination of β2 expression was observed in the periderm at E16. Coinciding with the differentiation of the epidermis, differential expression of α1 and β2 connexins was observed in the newly formed epidermal layers, α1 connexin was expressed in the basal and spinous layers, while β2 was confined to the differentiated spinous and granular layers. Large gap junctions were present in the basal layer, while small gap junctions, associated with many desmosomes, were typical for the differentiated layers. Although the distribution pattern for α1 and β2 expression remained the same in the neonatal and postnatal epidermis, the RNA and protein levels decreased markedly following birth. Hair follicle development was marked by expression of α1 connexin in hair germs at E16. Following β2 detection at E20, the expression increased for both α1 and β2 in developing follicles. A cell-type-specific expression was detected in the outer root sheath, in the matrix, in the matrix-derived cells (inner root sheath, cortex and medulla) and in the dermal papilla. In addition, α1 was specifically expressed in the arrector pili muscle, while sebocytes expressed both α1 and β3 (Cx31) connexin. β1 connexin (Cx32) was not detected at any stage analysed. The results indicate that multiple gap junction genes contribute to epidermal and follicular morphogenesis. Moreover, based on the utilization of gap junctions in all living cells of the surface epidermis, it appears that the epidermis may behave as a large communication compartment that may be coupled functionally to epidermal appendages (hair follicles and sebaceous glands) via gap junctional pathways.