林頌然醫師介紹 Study Highlights What Is Current Knowledge l Birds exhibit tremendously diverse feather pigment patterns that are important for their speciation. l Hair and feathers are organs of convergent evolution, but hair displays limited pigment pattern variation. l Avian feathers evolved from the skin of Jurassic feathered dinosaurs. Compared with the reptile ancestors endowed with multiple types of chromatophores, birds have only one pigment cell type, melanocyte. However, the variation in feather pigment patterns is no less than the pigment pattern variation of reptile skin. l Developmentally, melanocytes are derived from precursors originating from neural crest. However, the identity and location of feather melanocyte stem cells have long been uncertain. Questions addressed l Where are feather melanocyte stem cells? l What is the cellular and molecular mechanism for feather pigment pattern formation? l What is the evolutional basis for feather pigment pattern diversification? What Is New Here l Feather melanocyte stem cells are Mitf+ MART-1+ TRP-1- Tyrosinase apigmented cells located in the proximal feather epithelium and they send out differentiating progeny vertically up to paint the feather in the growing phase. In the resting phase, they become quiescent. l Three basic cellular mechanisms are employed by birds to create apigmentation: deletion of melanocyte stem cells, quiescence of melanocyte stem cells and inhibition of melanocyte stem cell differentiation. l Topologically, feather melanocyte stem cells are distributed as a ring in the bulge epithelium surrounding the proximal feather follicle. This niche topology confers greater temporospatial regulatory freedom. l A layer of feather peripheral pulp mesenchyme regulates pigmentation via patterned agouti expression to inhibit melanocyte differentiation. l The evolution of the multi-dimensional niche topology increases patterning possibilities, allowing various regulations to be choreographed with greater temporospatial freedom in the new morphogenetic space. l The complexity of avian pigment patterns is achieved by multiple-dimensional co-option of basic melanocyte behavior mechanisms during evolution. Extended Readings 1. Science 2013; Apr 25 [Epub ahead of print] . Topology of feather melanocyte progenitor niche allows complex pigment patterns to emerge. 2. Development, Growth & Differentiation 2013; 55:139-48.Feather regeneration as a model for organogenesis.
Posted on: Tue, 02 Jul 2013 13:36:23 +0000
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