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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! [ABSTRACT FROM AUTHOR]

The patterning of colors on birds is one of the most fascinating phenomena. Bird colors come from physical and chemical colors. Among the chemical colors are the melanin, carotenoids and porphyrins. Here we focus on the contribution of melanin to patterns on the feather vane of the Barred Plymouth Rocks and the Silver Laced Cochins. Tyrosinase plays an essential role in the process of melanogenesis. Understanding how tyrosinase activity is regulated during the formation of various feather color patterns may be the key to revealing the underlying patterning mechanisms. Using a modified tyramide-based tyrosinase assay, we examined the tyrosinase activity in regenerating feathers with barred or laced patterns. We showed that the tyrosinase activity is turned on prior to any visible melanin formation during the melanoblasts differentiation and persisted through the peak of melanin synthesis. The tyrosinase activity gradually disappeared along with the completion of feather development. Our results indicate that the tyrosinase activity is dynamically regulated with a pulse-like on/off pattern that obviously accounts for the ‘black’ and ‘white’ feather pigment pattern. Further study of the polymorphism of the tyrosinase gene and the difference in the regulation of tyrosinase activity in different pigment patterns is needed. [ABSTRACT FROM AUTHOR]