C/EBPalpha identifies differentiating preadipocytes around hair follicles in foetal and neonatal rat and mouse skin.

Previous studies have described a close anatomical association between hair follicles and subcutaneous adipocytes, yet little is known about the developmental origin of this preadipocyte population. Many transcription factors controlling adipogenesis in cell culture have been described; however, the molecular events governing the process of adipogenesis in rodent skin in vivo are largely unknown. In this study, we investigated the onset and progression of adipocyte differentiation in the skin of foetal and newborn rats and mice. We first analysed the temporo-spatial expression pattern of the transcription factor C/EBPalpha, a key player in adipocyte differentiation. Oil red O staining was then used to identify the presence of lipid within mature adipocytes in the same skin samples. In both species, nuclear staining of C/EBPalpha was first seen in cells around and below the bases of fully formed hair follicles in foetal dermis between 2 and 3 days before birth. Over time, increasing numbers of cells became labelled with C/EBPalpha, predominantly located between, rather than below, the hair follicles. Oil red O staining followed exactly the same pattern seen with the C/EBPalpha antibody, but with a delay of 12-24 h, and histomorphometry showed that the C/EBPalpha labelled cells matured into lipid filled adipocytes. These data show that C/EBPalpha is a useful developmental marker of preadipocytes in vivo. The close developmental association and physical proximity between the lower follicle and surrounding preadipocytes leads us to postulate that follicles control local adipogenic events, via signalling or by contributing to the preadipocyte pool.