Progressive Tooth Pattern Changes in Cilk1-Deficient mice Depending on Hedgehog Signaling
Primary cilia function as critical sensory organelles that mediate multiple signaling pathways, including the Hedgehog (Hh) pathway, which is essential for organ patterning and morphogenesis. Disruptions in Hh signaling have been implicated in supernumerary tooth formation and molar fusion in mutant mice. Cilk1, a highly conserved serine/threonine-protein kinase localized within primary cilia, plays a critical role in ciliary transport. Loss of Cilk1 results in severe ciliopathy phenotypes, including polydactyly, edema, and cleft palate. However, the role of Cilk1 in tooth development remains unexplored. In this study, we investigated the role of Cilk1 in tooth development. Cilk1 deficiency resulted in downregulation of Hh target genes, leading to the formation of supernumerary teeth. This study reveals a previously unrecognized role of Cilk1 in controlling tooth morphology via Hh signaling. Overall design: Cilk1 (Ciliogenesis associated kinase1) knockout  (Cilk1-/-) mice were generated by crossing Cilk1fl/fl mice with EIIa-Cre transgenic mice for Cre-mediated deletion of Cilk1 exon 6. Cilk1fl/fl mice were previously described  (https://doi.org/10.7554/eLife.56551).   Cilk1-/-;PCS1-MRCS1?/? mice were generated by crossing Cilk1-/- and PCS1-MRCS1?/? mice. PCS1-MRCS1?/? mice with a deletion of a 70 kb region from PCS1 to MRCS1 were previously described  (https://doi.org/10.1177/0022034518758642). All animal procedures were conducted in accordance with institutional guidelines and approved by the Institutional Animal Care and Use Committee  (IACUC) of Yonsei University. RNA was extracted from the maxillary molar tooth germs of Cilk1-/-, Cilk1-/-;PCS1-MRCS1?/? and Cilk1+/+ mice at embryonic day 14.5, followed by bulk RNA sequencing. Comparative gene expression profiling was then performed on the RNA-seq data.