Modulation of activin/bone morphogenetic protein signaling by follistatin is required for the morphogenesis of mouse molar teeth

Abstract

Teeth form as ectodermal appendages, and their morphogenesis is regulated by conserved signaling pathways. The shape of the tooth crown results from growth and folding of inner dental epithelium, and the cusp patterning is regulated by transient signaling centers, the enamel knots. Several signal proteins in the transforming growth factor-␤ (TGF␤) superfamily are required for tooth development. Follistatin is an extracellular inhibitor of TGF␤ signaling. To investigate the roles of follistatin during tooth development, we analyzed in detail the expression patterns of follistatin, activin ␤A, as well as Bmp2, Bmp4, and Bmp7 during tooth morphogenesis. We also examined the tooth phenotypes of follistatin knockout mice and of transgenic mice overexpressing follistatin in the epithelium under the keratin 14 (K14) promoter. The folding of the dental epithelium was aberrant in the molars of follistatin knockout mice, and the cusps were shallow with reduced cell proliferation and lack of anteroposterior polarization. The functions of both primary and secondary enamel knots were apparently disturbed. In K14 -follistatin transgenic mice, the molar cusp pattern was also seriously affected (although different from the follistatin knockouts) and the occlusal surfaces of the molars were whorled. Their enamel was prematurely worn. In addition, all of the third molars were missing. Our results indicate that follistatin regulates morphogenesis and shaping of the tooth crown. We propose that finely tuned antagonistic effects between follistatin and TGF␤ superfamily signals are critical for enamel knot formation and function, as well as for patterning of tooth cusps. Developmental Dynamics 231:98 -108, 2004.

Ectodysplasin has a dual role in ectodermal organogenesis: inhibition of Bmp activity and induction of Shh expression

“…The aberrant development of Eda -/-molars is evident from bud stage onwards and results in few shallow cusps associated with an overall smaller size of teeth Kangas et al, 2004). Intriguingly, ablation of Shh (Dassule et al, 2000) and follistatin (Wang et al, 2004b) leads to small teeth with fewer cusps.…”

“…The digoxigenin-labeled probes were detected with BM Purple AP Substrate Precipitating Solution (Boehringer Mannheim Gmbh, Germany). The following plasmids were used as templates: ameloblastin (Wang et al, 2004a); ␤-catenin, Edar and Shh (Laurikkala et al, 2002); follistatin (Wang et al, 2004b); and a 0.8 kb probe specific to the 3Ј end of Ccn2 (Friedrichsen et al, 2003). Noggin , gremlin (Khokha et al, 2001), Dan (Dionne et al, 2001) and bambi (Grotewold et al, 2001) probes were labelled with 35 S-UTP, and radioactive in situ hybridization on paraffin sections was performed according to standard procedures as described previously (Laurikkala et al, 2002).…”

“…Expression of gremlin is confined to the interplacodal mesenchyme during feather development (Ohyama et al, 2001). Interestingly, follistatin is expressed in the tooth, hair and feather placodes (Ferguson et al, 1998;Patel et al, 1999;Nakamura et al, 2003), and is localized to the enamel knot of E14 molar teeth (Wang et al, 2004b). Also Ccn2, a modular multifunctional protein with known ability to inhibit Bmp signalling (Abreu et al, 2002), is expressed in the epithelium of developing teeth, and is localized to the enamel knot of the cap stage tooth and is found later in preameloblasts (Shimo et al, 2002;Friedrichsen et al, 2003;Yamaai et al, 2005).…”

CCAAT/Enhancer-binding Protein δ (C/EBPδ) Maintains Amelogenin Expression in the Absence of C/EBPα in Vivo

“…The search for a promoter useful for driving Cre recombinase in ectoderm-derived ameloblasts identified the keratin 14 (K14) promoter (12)(13)(14)(15). Therefore, we used the K14 promoter to drive Cre-mediated recombination of floxed C/EBP␣ loci predicted to result in the loss of amelogenin expression.…”

Ectodysplasin regulates activator-inhibitor balance in murine tooth development through Fgf20 signaling

“…Experimentally manipulating the level of gene expression in the enamel knots results in variation of molar morphologies. For example, modulation of Shh, follistatin and Wnt signaling have been shown to result in altered molar shapes and cusp patterns (Dassule et al, 2000;Harjunmaa et al, 2012;Järvinen et al, 2006;Liu et al, 2008;Wang et al, 2004).…”