Molecular expression associated with vibrissa follicle development and differentiation

Abstract

The hair follicle is a complex mini-organ formed as a result of epithelial mesenchymal interactions, provided by three different stem cell sources: epithelial, neural crest and mesenchymal. Hair follicle morphogenesis is directed by a distinct set of molecular signals which are unique to each stage of development. These interactions continue into the adult cycle, represented by periods of rapid growth (anagen), apoptosis driven regression (catagen), a period of relative quiescence (telogen) and shedding of the club hair (exogen). Many of the molecules involved have been elucidated such as Wnts, Bmps, Fgfs, TGF-ßs and Shh amongst others. However, the nature of their regulation and effect on gene expression is still unclear. Id proteins are emerging as powerful players in the transcriptional control of many fundamental biological processes, such as the cell cycle, proliferation and differentiation, apoptosis and lineage commitment. As a result, the expression patterns of Id2 and Ids were investigated by immunocytochemistry in developing and adult vibrissae. Wistar rats aged E14toP4 were used to cover all stages of vibrissae development (stages 0-6+) and 3-6 month old rats for the adult stages. This thesis reports that high Id2 expression was seen in specialised neuroendocrine cells (Merkel cells) of the hair follicle and basal epidermis, confirmed by co-expression of the Merkel cell marker, cytokeratin-20. This post-mitotic Id2 expression continued through postnatal ages and into the adult follicle. Staining with Id3 was characterised by cytoplasmic, basally polarised expression in the epithelia of stage 1-4 follicles. After this stage, expression switched to being nuclear with high levels in many different cell types including the dermal papilla, dermal sheath and outer root sheath, ш and Id3 expression was also investigated in retinole acid induced differentiation of E13.5 and E14 mystacial pads, studying the glandular morphogenesis of vibrissae and the effect on Id protein expression. Ш and Id3 immunoreactivity was cytoplasmic and polarised but no evidence of nuclear staining was seen.Id2 and ИЗ expression in developing vibrissae is reported here for the first time, describing the profiles of these proteins during hair follicle development and differentiation. These findings highlight an important cytoplasmic role for Id proteins in development and may have implications for reciprocal epithelial- mesenchymal interactions, pattern formation and stem cells in the hair follicle.