Core Binding Factor Beta Functions in the Maintenance of Stem Cells and Orchestrates Continuous Proliferation and Differentiation in Mouse Incisors

Abstract

Rodent incisors grow continuously throughout life, and epithelial progenitor cells are supplied from stem cells in the cervical loop. We report that epithelial Runx genes are involved in the maintenance of epithelial stem cells and their subsequent continuous differentiation and therefore growth of the incisors. Core binding factor b (Cbfb) acts as a binding partner for all Runx proteins, and targeted inactivation of this molecule abrogates the activity of all Runx complexes. Mice deficient in epithelial Cbfb produce short incisors and display marked underdevelopment of the cervical loop and suppressed epithelial Fgf9 expression and mesenchymal Fgf3 and Fgf10 expression in the cervical loop. In culture, FGF9 protein rescues these phenotypes. These findings indicate that epithelial Runx functions to maintain epithelial stem cells and that Fgf9 may be a target gene of Runx signaling. Cbfb mutants also lack enamel formation and display downregulated Shh mRNA expression in cells differentiating into ameloblasts. Furthermore, Fgf9 deficiency results in a proximal shift of the Shh expressing cell population and ectopic FGF9 protein suppresses Shh expression. These findings indicate that Shh as well as Fgf9 expression is maintained by Runx/Cbfb but that Fgf9 antagonizes Shh expression. The present results provide the first genetic evidence that Runx/Cbfb genes function in the maintenance of stem cells in developing incisors by activating Fgf signaling loops between the epithelium and mesenchyme. In addition, Runx genes also orchestrate continuous proliferation and differentiation by maintaining the expression of Fgf9 and Shh mRNA.

Runx/Cbfb signaling regulates postnatal development of granular convoluted tubule in the mouse submandibular gland

“…To generate the Cbfb mutant mice, we first mated heterozygous K14‐Cre mice (Dassule et al, ) and homozygous Cbfb fl/fl mice (Naoe et al, ) to obtain F1 K14‐Cre/Cbfb fl/+ mice. The progeny were subsequently bred with Cbfb fl/fl mice (Kurosaka et al, ). The control group consisted of their littermates or knockout embryos that did not carry the K14‐Cre/Cbfb fl/fl genotype.…”

“…In situ hybridization was performed using 10 µm frozen sections or paraffin sections. In situ hybridization using digoxigenin‐labeled RNA probes was performed as previously described (Kurosaka et al, ). Murine Cbfb probes were generated from a 461 bp Cbfb fragment, as previously demonstrated (Kurosaka et al, ).…”

On the cutting edge of organ renewal: Identification, regulation, and evolution of incisor stem cells

“…Additional Fdfs , such as Fgf9 , are expressed in the incisor epithelium during development (Kettunen and Thesleff, ; Porntaveetus et al ., ) and may play key roles in initially activating the mesenchymal expression of FGFs (Bei and Maas, ; Wang et al ., ). Supporting this view, genetic ablation of the core binding factor β, which binds to Runx transcription factors and is required for the epithelial expression of Fgf9 , abrogated the expression of Fgf3 and Fgf10 in the developing dental mesenchyme (Kurosaka et al ., ).…”

“…The expression of Shh itself appears to be partially regulated by epithelial Fgf9 , at least during development. In this context, ectopic FGF9 suppressed Shh expression, while Fgf9 deficiency resulted in a proximal shift of the Shh expressing domain (Kurosaka et al ., ). Interestingly, this parallels some aspects of the developing limb, where FGF dependent Etv4/5 is required to limit the expression of Shh in the posterior limb bud mesenchyme and suppress Shh activity anteriorly (Mao et al ., ; Zhang et al ., ).…”

Distinct Role of Transforming Growth Factor-Beta 1 and Fibroblast Growth Factors in Human Amelobastoma Epithelial Cell Proliferation

“…The fibroblast cell growth factor (FGF) family has 22 members, 11 of which are expressed during tooth development [2]. Among these FGFs, the gene expression of FGF-9 and FGF-10 in dental epithelium is strongly involved in tooth development [3][4][5], and FGF-9 expression in the dental epithelium of mouse incisors regulates ameloblast differentiation [6]. Furthermore, FGF-9 or FGF-10 promotes in Human Amelobastoma Epithelial Cell Proliferation the cell proliferation of the dental epithelial progenitor cells established from rat incisors [7] and the dissociated epithelial cells detected in mouse molars [8].…”