Department of Biology, Research Institute, The Hospital for Sick Children, Toronto, ON M5G 0A4, Canada.
Program in Developmental and Stem Cell Biology, Research Institute, The Hospital for Sick Children, Toronto, ON M5G 0A4, Canada.
Development. 2024 Jun 15;151(12). doi: 10.1242/dev.202596. Epub 2024 Jun 17.
Apical expansion of calvarial osteoblast progenitors from the cranial mesenchyme (CM) above the eye is integral to calvarial growth and enclosure of the brain. The cellular behaviors and signals underlying the morphogenetic process of calvarial expansion are unknown. Time-lapse light-sheet imaging of mouse embryos revealed calvarial progenitors intercalate in 3D in the CM above the eye, and exhibit protrusive and crawling activity more apically. CM cells express non-canonical Wnt/planar cell polarity (PCP) core components and calvarial osteoblasts are bidirectionally polarized. We found non-canonical ligand Wnt5a-/- mutants have less dynamic cell rearrangements and protrusive activity. Loss of CM-restricted Wntless (CM-Wls), a gene required for secretion of all Wnt ligands, led to diminished apical expansion of Osx+ calvarial osteoblasts in the frontal bone primordia in a non-cell autonomous manner without perturbing proliferation or survival. Calvarial osteoblast polarization, progressive cell elongation and enrichment for actin along the baso-apical axis were dependent on CM-Wnts. Thus, CM-Wnts regulate cellular behaviors during calvarial morphogenesis for efficient apical expansion of calvarial osteoblasts. These findings also offer potential insights into the etiologies of calvarial dysplasias.
颅顶骨间充质（CM）上方颅骨祖细胞的顶端扩张对于颅骨生长和脑包绕是必不可少的。颅顶骨扩张的形态发生过程中细胞行为和信号尚不清楚。对小鼠胚胎的延时光片成像显示，颅顶骨祖细胞在眼上方的 CM 中进行 3D 穿插，并表现出更顶端的突起和爬行活性。CM 细胞表达非经典 Wnt/平面细胞极性（PCP）核心成分，颅顶成骨细胞呈双向极化。我们发现非经典配体 Wnt5a-/-突变体的细胞重排和突起活性较少。CM 特异性 Wntless（CM-Wls）缺失，一种所有 Wnt 配体分泌所必需的基因，导致额骨原基中 Osx+颅顶成骨细胞的顶侧扩张减少，这是一种非细胞自主的方式，而不会干扰增殖或存活。颅顶成骨细胞的极化、细胞的渐进伸长以及沿基底-顶端轴的肌动蛋白富集都依赖于 CM-Wnts。因此，CM-Wnts 调节颅顶骨形态发生过程中的细胞行为，以实现颅顶骨祖细胞的高效顶侧扩张。这些发现还为颅顶骨发育不良的病因提供了潜在的见解。
