RSK2 is a modulator of craniofacial development

The RSK2 gene is responsible for Coffin-Lowry syndrome, an X-linked monogenic disease associating severe learning deficit andassociated to typical facial and digital abnormalities and skeletal changes. Craniofacial and dental anomalies encountered in this rare disease have been poorly characterized. In this study we explore, through X-Ray microtomographic analysis, the variable craniofacial dysmorphism and dental anomalies present in Rsk2 knockout mice, an animal model of Coffin-Lowry syndrome, as well as in triple Rsk1,2,3 knockout mutants. We report in these mutants the occurrence of a surpernumerary tooth mesial to the first molar. This highly penetrant phenotype is considered as a remnant of evolutionary lost teeth. This possibly leads to the significant reduction of the maxillary diastema. Abnormalities of molar shape were almost restricted to the mesial part of both upper and lower first molars (M1). We also report an expression analysis of the four Rsk genes (Rsk1, 2, 3 and 4) at various stages of odontogenesis in wild-type (WT) mice. Rsk2 was mainly expressed in the mesenchymal, neural crest derived compartment, correlating with proliferative areas of the developing teeth and consistent with a biological function of RSK2 in cell cycle control and cell growth, which when invalidated could be responsible for the dental phenotype. In an attempt to unravel the molecular pathways involved in the genesis of these dental defects, we performed a comparative transcriptomic (DNA microarray) analysis of mandibular wild-type versus Rsk2-/Y molars, and further demonstrated a misregulation of selected genes, using a Rsk2 shRNA knock-down strategy in molar tooth germs cultured in vitro.