SATB1 Modulates the Transcriptional Programming of Secretory Ameloblasts

Objectives: Ameloblasts progress through multiple stages of differentiation to craft enamel tissues. This intricate developmental process starts with secretory ameloblasts (SABs), which are responsible for secreting enamel matrix proteins (EMPs) into the extracellular space for enamel formation. The chromatin organizer-specific AT-rich sequence binding protein 1 (SATB1) is significantly upregulated in the presecretory ameloblasts. In this study, we aim to investigate the role of SATB1 in the progression from presecretory ameloblasts to secretory ameloblasts (SABs).
Methods: Histological examinations were conducted on the incisors and molars of mice with dysfunctional SATB1. RNA-seq analyses were employed to compare the whole transcriptome of SABs from Satb1^+/+ and Satb1^-/- mouse molars. The expression levels of potential SATB1 target genes were subsequently validated through RT-qPCR and immunostaining. Mouse molar organs were cultured in the presence of trichostatin A (TSA), a histone deacetylase inhibitor, to investigate the correlation between histone acetylation and EMP expression within SABs.
Results: Deletion of functional SATB1 led to disorganized SABs and enamel dysplasia on both incisors and molars. RNA-seq analyses revealed that SATB1 was critical for the upregulation of ameloblastin and enamelin, and genes associated with ameloblast polarization. RNAscope indicated that the absence of SATB1 delayed the onset of enamelin and ameloblastin expression. In response to increased histone acetylation, secretory stage of enamel organ cells in the organ culture exhibited greater than a four-fold increase in both ameloblastin and enamelin levels. This finding aligns with a prediction in which a super-enhancer, marked by H3K27ac, was established in the transcriptional regulatory region of the enamelin and ameloblastin gene cluster. Immunofluorescence imaging unveiled a substantial reduction in H3K27ac levels in the Satb1^-/- SABs when compared to their wild-type counterparts.
Conclusions: The findings demonstrate that SATB1 is critical for secretory ameloblast differentiation by establishing a super-enhancer to govern the transcription of ameloblast stage-specific biomarkers, ameloblastin and enamelin.