Mapping stem cell activities in the feather follicle

Abstract

It is important to know how different organs 'manage' their stem cells. Both hair and feather follicles show robust regenerative powers that episodically renew the epithelial organ. However, the evolution of feathers (from reptiles to birds) and hairs (from reptiles to mammals) are independent events and their follicular structures result from convergent evolution. Because feathers do not have the anatomical equivalent of a hair follicle bulge, we are interested in determining where their stem cells are localized. By applying long-term label retention, transplantation and DiI tracing to map stem cell activities, here we show that feather follicles contain slow-cycling long-term label-retaining cells (LRCs), transient amplifying cells and differentiating keratinocytes. Each population, located in anatomically distinct regions, undergoes dynamic homeostasis during the feather cycle. In the growing follicle, LRCs are enriched in a 'collar bulge' niche. In the moulting follicle, LRCs shift to populate a papillar ectoderm niche near the dermal papilla. On transplantation, LRCs show multipotentiality. In a three-dimensional view, LRCs are configured as a ring that is horizontally placed in radially symmetric feathers but tilted in bilaterally symmetric feathers. The changing topology of stem cell activities may contribute to the construction of complex feather forms.

Morphoregulation of avian beaks: Comparative mapping of growth zone activities and morphological evolution

“…Our recent work on the mapping of feather stem cells shows that the different relative positioning of stem cells and transient amplifying cells (TA cells in ectodermal organogenesis terminology; they are also defined by a short BrdU labeling and are equivalent to the LoGZ here) can lead to different feather morphologies. Specifically, stem cells are configured as a ring, positioned horizontally in the radially symmetric downy feathers but tilted anteriorly in bilaterally symmetric feathers (Yue et al, 2005). An anterior-posterior Wnt 3a gradient is critical for forming the bilateral but not radial symmetry of feathers (Yue et al, 2006).…”

Follicular patterns during feather morphogenesis in relation to the formation of asymmetric feathers, filoplumes and bristles

“…Recent studies have suggested that the ramogenic plane becomes tilted in pennaceous feathers, so that the growth of barb ridges determines their fusion into a rachis (Yue et al 2005(Yue et al , 2006. The change in orientation of the ramogenic plane may be derived from unknown messages probably coming from the dermal papilla.…”

“…It has been proposed (Yue et al 2005(Yue et al , 2006) that in downfeathers the ramogenic plane is horizontal so that growing barb ridges remain separated and implanted in a basal calamus (Figures 8 AA1, A2, A3; different colours indicate successive addition of Figure 6. Cross-section of upper follicle of asymmetric chicken wing feathers.…”

“…The latter continues distally into a loose connective indicated as pulp. Recent studies have identified in the upper part of the collar, a pimple-like region indicated as bulge, where stem cells for the cyclical regeneration of feathers are localized (Yue et al 2005).…”

“…The colour version of this figure is available online. Yu et al 2002;Chuong et al 2003;Yue et al 2005Yue et al , 2006Lin et al 2006). …”