NF-κB transmits Eda A1/EdaR signalling to activate Shh and cyclin D1 expression, and controls post-initiation hair placode down growth

Abstract

A novel function of NF-B in the development of most ectodermal appendages, including two types of murine pelage hair follicles, was detected in a mouse model with suppressed NF-B activity (c IB␣⌬N ). However, the developmental processes regulated by NF-B in hair follicles has remained unknown. Furthermore, the similarity between the phenotypes of c IBA⌬N mice and mice deficient in Eda A1 (tabby) or its receptor EdaR (downless) raised the issue of whether in vivo NF-B regulates or is regulated by these novel TNF family members. We now demonstrate that epidermal NF-B activity is first observed in placodes of primary guard hair follicles at day E14.5, and that in vivo NF-B signalling is activated downstream of Eda A1 and EdaR. Importantly, ectopic signals which activate NF-B can also stimulate guard hair placode formation, suggesting a crucial role for NF-B in placode development. In downless and c IB␣⌬N mice, placodes start to develop, but rapidly abort in the absence of EdaR/NF-B signalling. We show that NF-B activation is essential for induction of Shh and cyclin D1 expression and subsequent placode down growth. However, cyclin D1 induction appears to be indirectly regulated by NF-B, probably via Shh and Wnt. The strongly decreased number of hair follicles observed in c IB␣⌬N mice compared with tabby mice, indicates that additional signals, such as TROY, must regulate NF-B activity in specific hair follicle subtypes.

Generation and Characterization of Function-blocking Anti-ectodysplasin A (EDA) Monoclonal Antibodies That Induce Ectodermal Dysplasia

“…Antibodies were purified from conditioned supernatants of hybridoma grown in DMEM containing 10% low Ig fetal calf serum (Invitrogen) or Opti-MEM by affinity chromatography on protein G-Sepharose (GE Healthcare). Anti-EDA monoclonal antibody Renzo-2 and anti-APRIL monoclonal 4 Cl, and buffer was exchanged for PBS (10 mM sodium-potassium phosphate, 140 mM NaCl, pH 7.2) by diafiltration.…”

“…For example, in tooth buds after the placode stage, EDAR is expressed in the enamel knots, which are nonproliferating signaling centers that guide the shaping of the tooth crown (6,7). The observation of morphological abnormalities in hair from Eda-deficient mice further suggests a role for EDA in the regulation of hair morphogenesis at a postplacodal stage (4). In particular, localization of Shh expression by Wnt and EDA affects axial polarity and shape of hairs (8).…”

“…The action of the TNF family ligand EDA 2 on its receptor EDAR, a target gene of Wnt signaling, is required shortly thereafter at least for sweat glands and some hair types, to stimulate the transcription factor NF-B, itself necessary for the formation of morphologically distinct cellular condensates called placodes (3,4). Some placodes, such as those of guard hair developing at embryonic day (E) 14.5, are fully dependent on EDA-EDAR interactions and NF-B for their formation, whereas others, such as those of undercoat hair developing at around birth, can form in the absence of EDA but produce morphologically abnormal hair (4). In the skin, a pattern of regularly spaced placodes forms as a result of sustained EDAR activation within placodes that induces strong inhibitory signals at the placode periphery.…”

Biology of Human Hair: Know Your Hair to Control It

“…On the other hand, forced activation of b-catenin signaling promotes HF fate in both embryonic and postnatal skin [67,[73][74][75]. Recent studies also suggest that another pathway, the ectodysplasin signaling pathway, is critical for the induction and maintenance of placode [76,77].…”

EDA Signaling and Skin Appendage Development

“…34,43 We also found two new isoforms, A5 and A5', which bind to EDAR and XEDAR, respectively, and activate NFkBs in vitro. 42 Especially 15,45,46 Another EDAR family member, Troy, is also highly expressed in skin appendages. 46,47 To understand Troy function, we generated a mutant mouse strain by ENU mutagenesis (unpublished results).…”