Early stages of hair follicle development: a step by step microarray identity.

Hair follicle morphogenesis requires an epithelial-mesenchymal cross-talk during development, from hair placode to hair peg, and finally hair follicle formation. During this step, factors known as activators and inhibitors allow the patterning distribution of hair follicle within the skin. Our goal was to investigate the modulation of expression of various factors already known to be part of the hair placode formation, and to identify novel factors involved during the initiation of this process. In mice, primary hair follicles arise in utero from E12.5 mouse embryos. Back skin RNA were extracted from E12.5 to E14.5 embryos to perform microarray analysis (Affymetrix). We identified four new Wnt related genes which could be involved in hair follicle initiation because of their maximum expression at E12.5, namely two activators: Wnt-2 and Zic-1 and two inhibitors: Dkk-2 and Dact-1. Real-time quantitative polymerase chain reactions confirmed their expression. Our data provide a more precise view of transcript expressions involved during induction of HF morphogenesis, particularly the hair primordium formation.

What is the biological basis of pattern formation of skin lesions?

Pattern recognition is at the heart of clinical dermatology and dermatopathology. Yet, while every practitioner of the art of dermatological diagnosis recognizes the supreme value of diagnostic cues provided by defined patterns of 'efflorescences', few contemplate on the biological basis of pattern formation in and of skin lesions. Vice versa, developmental and theoretical biologists, who would be best prepared to study skin lesion patterns, are lamentably slow to discover this field as a uniquely instructive testing ground for probing theoretical concepts on pattern generation in the human system. As a result, we have at best scraped the surface of understanding the biological basis of pattern formation of skin lesions, and widely open questions dominate over definitive answer. As a symmetry-breaking force, pattern formation represents one of the most fundamental principles that nature enlists for system organization. Thus, the peculiar and often characteristic arrangements that skin lesions display provide a unique opportunity to reflect upon--and to experimentally dissect--the powerful organizing principles at the crossroads of developmental, skin and theoretical biology, genetics, and clinical dermatology that underlie these--increasingly less enigmatic--phenomena. The current 'Controversies' feature offers a range of different perspectives on how pattern formation of skin lesions can be approached. With this, we hope to encourage more systematic interdisciplinary research efforts geared at unraveling the many unsolved, yet utterly fascinating mysteries of dermatological pattern formation. In short: never a dull pattern!