Primary cilia regulate Shh activity in the control of molar tooth number.
Primary cilia mediate Hh signalling and mutations in their protein components affect Hh activity. We show that in mice mutant for a cilia intraflagellar transport (IFT) protein, IFT88/polaris, Shh activity is increased in the toothless diastema mesenchyme of the embryonic jaw primordia. This results in the formation of ectopic teeth in the diastema, mesial to the first molars. This phenotype is specific to loss of polaris activity in the mesenchyme since loss of Polaris in the epithelium has no detrimental affect on tooth development. To further confirm that upregulation of Shh activity is responsible for the ectopic tooth formation, we analysed mice mutant for Gas1, a Shh protein antagonist in diastema mesenchyme. Gas1 mutants also had ectopic diastema teeth and accompanying increased Shh activity. In this context, therefore, primary cilia exert a specific negative regulatory effect on Shh activity that functions to repress tooth formation and thus determine tooth number. Strikingly, the ectopic teeth adopt a size and shape characteristic of premolars, a tooth type that was lost in mice around 50-100 million years ago.
Ohazama
Atsushi
A
Department of Craniofacial Development, Dental Institute, King's College London, London SE1 9RT, UK.
Haycraft
Courtney J
CJ
Seppala
Maisa
M
Blackburn
James
J
Ghafoor
Sarah
S
Cobourne
Martyn
M
Martinelli
David C
DC
Fan
Chen-Ming
CM
Peterkova
Renata
R
Lesot
Herve
H
Yoder
Bradley K
BK
Sharpe
Paul T
PT
D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002923:Cilia / Q000378:metabolism; D003970:Diastema; D058851:GPI-Linked Proteins; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D014070:Tooth / Q000254:growth & development / Q000378:metabolism*
D018797:Cell Cycle Proteins; D058851:GPI-Linked Proteins; C501180:Gas1 protein, mouse; D053823:Hedgehog Proteins; D008565:Membrane Proteins; C465570:Shh protein, mouse