019 Cyclin D-Interacting Myb-Like Protein: A New Regulator of Cortical Cell Proliferation and Differentiation in Hair Follicles

Z.D. Yu1,2, A.J. Nixon1, R.J. Wilkins2, and A.J. Pearson1 1AgResearch Ruakura, Hamilton, New Zealand. 2Dept. Biological Sciences, University of Waikato, Hamilton, New Zealand

Hair arises from the proliferation of epithelial cells in the follicle bulb which subsequently undergo a highly regulated differentiation programme. This study reports the discovery of a transcription factor expressed in the keratogenous zone of hair follicles which potentially influences this process. Flank skin samples were collected from prepubertal ferrets between 0 and 14 days after treatment with melatonin to synchronise the winter moult. Differential display was used to analyse RNA extracts. Differential expression was confirmed by Northern blot and in situ hybridisation. Additional sequence was generated using rapid amplification of cDNA ends (RACE). A cDNA band of approximately 170 bp, which was present only in skin samples with anagen follicles, was identified and cloned. The cDNA sequence showed high homology to a region within the coding sequence of human and mouse cyclin D-interacting myb-like protein 1 (DMP1). Northern blot analysis confirmed that a mRNA of 0.9 kb existed only in skin samples containing follicles in which keratinisation had commenced. In situ hybridisation demonstrated that this gene was expressed uniformly across the cortex only in the keratinisation zone of late proanagen and anagen hair follicles, but not in liver, footpad skin or muscle. A 760 bp sequence was extended to the 5’ end by RACE. The first 176 encoded amino acids of ferret DMP1 were 98% identical to the human homologue. DMP1 is known to be expressed in a variety of human and mouse tissues and to inhibit cell division by arresting the cell cycle in the G1 phase in a pRb-independent manner. It is phosphorylated by cyclin Ddependent kinase and cyclin D represses DMP1 transactivation activity by preventing DNA binding and transcription of the targeted genes. Disruption of DMP1 thus facilitates cell transformation and tumorigenesis. Based on its restricted expression in anagen follicles and its smaller size, the ferret homologue is possibly an alternatively spliced form of DMP1 with hair follicle specific functions. As keratinocyte replication ceases in the area of the follicle where fDMP1 is expressed, this gene product may be associated with arrest of cortical cell growth and promotion of differentiation.