A pair of transmembrane receptors essential for the retention and pigmentation of hair.

ABSTRACT

Hair follicles are simple, accessible models for many developmental processes. Here, using mutant mice, we show that Bmpr2, a known receptor for bone morphogenetic proteins (Bmps), and Acvr2a, a known receptor for Bmps and activins, are individually redundant but together essential for multiple follicular traits. When Bmpr2/Acvr2a function is reduced in cutaneous epithelium, hair follicles undergo rapid cycles of hair generation and loss. Alopecia results from a failure to terminate hair development properly, as hair clubs never form, and follicular retraction is slowed. Hair regeneration is rapid due to premature activation of new hair-production programs. Hair shafts differentiate aberrantly due to impaired arrest of medullary-cell proliferation. When Bmpr2/Acvr2a function is reduced in melanocytes, gray hair develops, as melanosomes differentiate but fail to grow, resulting in organelle miniaturization. We conclude that Bmpr2 and Acvr2a normally play cell-type-specific, necessary roles in organelle biogenesis and the shutdown of developmental programs and cell division.