Modulation of Bmp4 signalling in the epithelial-mesenchymal interactions that take place in early thymus and parathyroid development in avian embryos

► We used the quail-chick system to study gland formation by the pharyngeal endoderm. ► Foxn1 and Gcm2 identify avian thymic and parathyroid epithelia, respectively. ► Early thymus and parathyroid development requires mesenchymal-derived Bmp4. ► Later on, Bmp4 in the mesenchyme becomes dispensable and is replaced by Fgf10. ► PP3/4 endoderm associated with permissive mesenchyme gives rise to a thymus.