Identification of dkk4 as a target of Eda-A1/Edar pathway reveals an unexpected role of ectodysplasin as inhibitor of Wnt signalling in ectodermal placodes.
The development of epithelial appendages, including hairs, glands and teeth starts from ectodermal placodes, and is regulated by interplay of stimulatory and inhibitory signals. Ectodysplasin-A1 (Eda-A1) and Wnts are high in hierarchy of placode activators. To identify direct targets of ectodysplasin pathway, we performed microarray profiling of genes differentially regulated by short exposure to recombinant Eda-A1 in embryonic eda(-/-) skin explants. Surprisingly, there were only two genes with obvious involvement in Wnt pathway: dkk4 (most highly induced gene in the screen), and lrp4. Both genes colocalized with Eda-A1 receptor Edar in placodes of ectodermal organs. They were upregulated upon Edar activation while several other Wnt associated genes previously suggested as Edar targets were unaffected. However, low dkk4 and lrp4 expression was retained in the absence of NF-kappaB signalling in eda(-/-) hair placodes. We provide evidence that this expression was dependent on Wnt activity present prior to Eda-A1/Edar signalling. Dkk4 was recently suggested as a key Wnt antagonist regulating lateral inhibition essential for correct patterning of hair follicles. Several pieces of evidence suggest Lrp4 as a Wnt inhibitor, as well. The finding that Eda-A1 induces placode inhibitors was unexpected, and underlines the importance of delicate fine-tuning of signalling during placode formation.
Institute of Biotechnology, Developmental Biology Program, University of Helsinki, 00014, Helsinki, Finland.
Ingrid
I
Fliniaux
Marja L
ML
Mikkola
Sylvie
S
Lefebvre
Irma
I
Thesleff
D000818:Animals; D001665:Binding Sites; D004475:Ectoderm / Q000166:cytology / Q000196:embryology*; D053331:Ectodysplasins / Q000378:metabolism*; D053339:Edar Receptor / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000166:cytology; D005260:Female; D018507:Gene Expression Regulation, Developmental; D018859:Hair Follicle / Q000166:cytology / Q000196:embryology; D066298:In Vitro Techniques; D036341:Intercellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008954:Models, Biological; D009024:Morphogenesis; D016328:NF-kappa B / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic / Q000235:genetics; D015398:Signal Transduction; D012867:Skin / Q000166:cytology / Q000196:embryology; D015854:Up-Regulation; D051153:Wnt Proteins / Q000378:metabolism*
C513131:Dkk4 protein, mouse; D053331:Ectodysplasins; D053339:Edar Receptor; D036341:Intercellular Signaling Peptides and Proteins; D016328:NF-kappa B; D051153:Wnt Proteins