Dermal condensation formation in the chick embryo: Requirement for integrin engagement and subsequent stabilization by a possible Notch/integrin interaction

Abstract

During embryonic development, feathers appear first as primordia consisting of an epidermal placode associated with a dermal condensation. When 7-day chick embryo dorsal skin fragments showing three rows of feather primordia are cultured, they undergo a complete reorganization, which involves the downregulation of morphogenetic genes and dispersal of dermal fibroblasts, leading to the disappearance of primordia. This loss of organisation is followed by de novo differentiation events. We have used this model to study potential factors involved in the formation of dermal condensations. Activation of Integrins by extracellular Manganese or intracellular Calcium prevents the initial disappearance of the dermal condensations. New primordia formation occurs even after inhibition of the Notch pathway albeit with some fusion between primordia. In conclusion, dermal fibroblast migration requires ␤1-Integrin whereas the stability of dermal condensations could depend on Notch/Integrin interaction. Developmental Dynamics 236:755-768, 2007.

BMP2 and BMP7 play antagonistic roles in feather induction

“…By contrast, in semi-apteria the cell density remains under this threshold, reaching only up to 2.0 nuclei/1000 μm 3 (Olivera-Martinez et al, 2001). We have shown previously (Michon et al, 2007) that when cell density exceeds the threshold, proliferation stops and there is a redistribution of cells to form dermal condensations, where the cell density reaches 5.52 nuclei/1000 μm 3 (Wessels, 1965). These dermal condensations arise under the epidermal placodes.…”

“…Second, we studied in vitro dermal fibroblast behavior in response to different BMPs. Both fibroblast migration (Mauger et al, 1982) and Fibronectin (Chuong, 1993;Michon et al, 2007) have been implicated in the transition from a dense dermis to individual dermal condensations. Alternative splicing of the fibronectin gene has been identified as a key regulator of Fibronectin/Integrin affinity in CHO cells (Manabe et al, 1997).…”

Evidence that Notch and Delta expressions have a role in dermal condensate aggregation during wool follicle initiation

“…Notch signalling appears to be critical for condensate formation, see also (13). DAPT treatment of cultures abolished papilla cell aggregation and inhibited or delayed follicle initiation, implicating receptor activation as a prerequisite for clustering.…”

“…Although Fehon et al (24) reported that cells lacking Notch or Delta did not aggregate with Notch+ and Delta+ cells, it seems likely that other adhesion mechanisms would be exploited (13,27).…”

“…Prior to follicle initiation, vertebrate skin appears to be composed of relatively homogeneous populations of cells (13,14). However, the focal migrations evident during initiation suggested that the fates of some cells may have already been established.…”