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

Abstract

C/EBP␣ is implicated to regulate mouse amelogenin gene expression during tooth enamel formation in vitro. Because enamel formation occurs during postnatal development and C/EBP␣-deficient mice die at birth, we used the Cre/loxP recombination system to characterize amelogenin expression in C/EBP␣ conditional knock-out mice. Mice carrying the Cre transgene under the control of the human keratin-14 promoter show robust Cre expression in the ameloblast cell lineage. Mating between mice bearing the floxed C/EBP␣ allele with keratin-14-Cre mice generate C/EBP␣ conditional knock-out mice.Real-time PCR analysis shows that removal of one C/⌭〉P␣ allele from the molar enamel epithelial organ of 3-day postnatal mice results in dramatic decrease in endogenous C/⌭〉P␣ mRNA levels and coordinately altered amelogenin mRNA abundance. Conditional deletion of both C/EBP␣ alleles further diminishes C/EBP␣ mRNA levels; however, rather than ablating amelogenin expression, we observe wild-type amelogenin mRNA abundance levels. We examined C/EBP␤ and nuclear factor YA expression, two transcription factors that had previously been shown to modestly participate in amelogenin expression, in vitro but found no significant changes in either of their mRNA abundance levels comparing conditional knock-out mice with wild-type counterparts. Although the abundance of C/EBP␦ is also unchanged in C/EBP␣ conditional knock-out mice, in vitro we find that C/EBP␦ activates the mouse amelogenin promoter and synergistically cooperates with nuclear factor Y, suggesting that C/EBP␦ can functionally substitute for C/EBP␣ to produce an enamel matrix competent to direct biomineralization.

The Circadian Clock Modulates Enamel Development

“…Gene outputs can be either directly induced by the transcription factors of the circadian oscillator (CLOCK-BMAL1) or activated via specific effectors, which are responsive to the circadian transcription factors (Schibler et al, 2003). As shown in this study, the expression of Nfya , a recognized positive transcriptional activator of Amelx (Xu et al, 2006, 2007), oscillates in cultured ameloblasts with a daily rhythm (Fig. 2B).…”

Transcription Factor FoxO1 Is Essential for Enamel Biomineralization

“…One member, C/EBPα, was shown to be a transcriptional activator of the mouse Amelogenin gene in vitro . Interestingly, ameloblast specific ablation of C/EBPα did not result in an enamel phenotype or loss of Amelogenin expression and this was shown to be due to redundancy with C/EBPδ [58], [59]. By employing future bioinformatic experiments to map FoxO/Smad binding elements, we should be able to uncover more putative target genes.…”

Regulation of Dental Enamel Shape and Hardness

“…The second (transition to maturation) initiates kallikrein 4, amelotin, and odam (apin) expression (Hu et al, 2000; Moffatt et al, 2006b; Moffatt et al, 2008), reformation of a glycoprotein-rich basal lamina on the surface of the enamel (Al Kawas and Warshawsky, 2008; Sawada and Inoue, 2001), and some ameloblast apoptosis (Bronckers et al, 2000; Joseph et al, 1994; Kondo et al, 2001). Perhaps continued characterization of the transcription factors that regulate amelogenin gene expression will provide insights into the developmental mechanisms that mediate the initial differentiation and later transition of ameloblasts (Adeleke-Stainback et al, 1995; Gibson, 1999; Xu et al, 2009; Xu et al, 2006; Xu et al, 2007a; Xu et al, 2007b; Zhou and Snead, 2000). A rat wct (whitish chalk-like teeth) mutant exhibits an arrest of enamel formation at the ameloblast transition (Masuyama et al, 2005; Osawa et al, 2007).…”