The Dynamic Spatiotemporal Distribution Of Ctsk+ Suscs During Skull Development

To delineate the spatiotemporal distribution patterns of Ctsk+ suture mesenchymal stem cells (SuSCs) in different cranial suture regions. Murine specimens from CtskLacZ and Ctskcre, Rosa26LSL-tdtomato genetic lines were collected at postnatal days 7, 14, 28, and 8 months. Whole-mount β-galactosidase staining coupled with stereomicroscopy and histomorphometric analysis were performed on calvarial preparations. Fluorescence stereomicroscopy and immunofluorescence co-localization studies were systematically conducted, with specific emphasis on spatial relationships between Ctsk+ cells and Gli1+ SuSCs. Overall, Ctsk-expressing cells were mainly distributed at the osteogenic front of cranial sutures and the center of cranial bone plates, widely present in all cranial sutures, and a small number of Ctsk+ cells were also found in the cranial base cartilage area. During development, they gradually concentrated towards the cranial sutures and osteogenic fronts, with a decrease in the bone plate center. Microscopically, Ctsk+ cells were distributed in the suture mesenchyme, osteogenic fronts, periosteum and dura mater, and partially co - localized with Gli1, a classic suture stem cell marker. Ctsk+ cells are widely distributed in mouse cranial sutures at different stages. During development, they tend to concentrate in cranial suture regions, and their distribution partially overlaps with Gli1, suggesting that Ctsk+ SuSCs may play a key role in suture development.This work establishes the dynamic redistribution of Ctsk+ SuSCs toward suture-resident niches during murine calvarial maturation, providing critical insights for developing suture-biomimetic strategies in cranial regenerative medicine.