Hair follicle germinative epidermal cells : a molecular study
At the base of the hair follicle epidermal matrix is a population of germinative epidermal (GE) cells that is in close communication with the dermal papilla. These GE cells are at the core of activities that comprise the fundamental processes of cell signalling and differentiation in the hair follicle. Since it is in the germinative region that the signals that produce hair are being received and transcribed, identification of genes expressed in the GE cells will be important for our understanding of hair growth control and the molecular mechanisms operating at the site of epidermal proliferation and differentiation. This study describes the production of a series of cDNA libraries, both by conventional means from rat vibrissa follicles and follicle end bulbs, and by PGR from the GE cells and the tissues of the upper end bulb. These libraries were then used for a variety of screening approaches to isolate cDNA clones, firstly for molecules which are known to be involved in the control of hair growth, and secondly for molecules which are differentially expressed in the follicular germinative epidermis. In order to identify such preferentially expressed genes, a dual labelling differential screen of the vibrissa follicle end bulb cDNA library was performed, using probes derived from the germinative epidermal and upper end bulb PGR generated libraries. Nine putative differentially expressed clones were isolated and sequenced. RNase protection analysis and non radioactive in situ hybridisation was then performed to confirm that these clones were expressed in the germinative epidermis of rat vibrissa follicles. Further characterisation by northern blotting revealed that several of the clones were expressed in multiple tissues. Nucleotide sequence analysis revealed that six of the clones had a concensus BG1 repeat sequence at the end of their 3'UTR. This has been implicated in post-transcriptional control of intracellular mRNA localisation. Three of these clones were related to genes implicated in induction and vesicle trafficking. These clones may therefore be involved in the signal transduction pathways operating in the germinative epidermis in response to primary signalling molecules received from the dermal papilla.