Integration of FGF and TWIST in calvarial bone and suture development

Abstract

Mutations in the FGFR1-FGFR3 and TWIST genes are known to cause craniosynostosis, the former by constitutive activation and the latter by haploinsufficiency. Although clinically achieving the same end result, the premature fusion of the calvarial bones, it is not known whether these genes lie in the same or independent pathways during calvarial bone development and later in suture closure. We have previously shown that Fgfr2c is expressed at the osteogenic fronts of the developing calvarial bones and that, when FGF is applied via beads to the osteogenic fronts, suture closure is accelerated (Kim, H.-J., Rice, D. P. C., Kettunen, P. J. and Thesleff, I. (1998) Development 125, 1241–1251). In order to investigate further the role of FGF signalling during mouse calvarial bone and suture development, we have performed detailed expression analysis of the splicing variants of Fgfr1-Fgfr3 and Fgfr4, as well as their potential ligand Fgf2. The IIIc splice variants of Fgfr1-Fgfr3 as well as the IIIb variant of Fgfr2 being expressed by differentiating osteoblasts at the osteogenic fronts (E15). In comparison to Fgf9, Fgf2 showed a more restricted expression pattern being primarily expressed in the sutural mesenchyme between the osteogenic fronts. We also carried out a detailed expression analysis of the helix-loop-helix factors (HLH) Twist and Id1 during calvaria and suture development (E10-P6). Twist and Id1 were expressed by early preosteoblasts, in patterns that overlapped those of the FGF ligands, but as these cells differentiated their expression dramatically decreased. Signalling pathways were further studied in vitro, in E15 mouse calvarial explants. Beads soaked in FGF2 induced Twist and inhibited Bsp, a marker of functioning osteoblasts. Meanwhile, BMP2 upregulated Id1. Id1 is a dominant negative HLH thought to inhibit basic HLH such as Twist. In Drosophila, the FGF receptor FR1 is known to be downstream of Twist. We demonstrated that in Twist(+/)(−) mice, FGFR2 protein expression was altered. We propose a model of osteoblast differentiation integrating Twist and FGF in the same pathway, in which FGF acts both at early and late stages. Disruption of this pathway may lead to craniosynostosis.

C-reactive protein promotes bone destruction in human myeloma through the CD32–p38 MAPK–Twist axis

“…Initially identified in Drosophila where it is involved in mesodermal patterning and morphogenetic movement (23), Twist is a highly conserved protein and a master regulator of morphogenesis. Previous studies have also shown that Twist is important in bone development and is expressed in primary osteoblastic cells (24) and preosteoblasts (25). In situ analysis of murine embryonic development provided evidence that Twist abundance is reduced during endochondral and intramembranous fetal bone development (26).…”

Revealing the Critical Regulators of Modulated Smooth Muscle Cells in Atherosclerosis in Mice

“…Intriguingly, consistent with the continuous transition mode as revealed by transcriptional and functional repertoires of mSMCs, a similar mode was observed in the regulatory network ( Figure 3B ). In addition, mSMC-associated modules (namely, M1, M4, and M5) included several reported ossification- or calcification-related TFs, including Dlx5 ( Shirakabe et al, 2001 ), Sox9 ( Augstein et al, 2018 ), Runx2 ( Byon et al, 2011 ), Rarg ( Pan et al, 2020 ), and Twist1 ( Rice et al, 2000 ; Bialek et al, 2004 ) Finally, we explored the distribution model of the top 20 cell-type-specific regulons for each cell type in eight modules and represented in a Sankey plot ( Figure 3C ). The results were showed for a specific cell type, and the top 20 regulons concentrated primarily in a module (e.g., top 20 regulons of SMCs in M3).…”

The molecular complex of ciliary and golgin protein is critical for skull development

“…Between adjacent skull bones, OFs are present within the developing suture consisting of fibrous joints (Morriss-Kay and Wilkie, 2005;Rice et al, 2000;Wilkie and Morriss-Kay, 2001). Growth at the OFs occurs through intramembranous ossification, by which osteoprogenitors proliferate and differentiate directly into osteoblasts (Iseki et al, 1997(Iseki et al, , 1999.…”

“…During skull development, growth at the osteogenic fronts (OFs) occurs via intramembranous ossification, in which mesenchymal osteoprogenitors proliferate and differentiate directly into osteoblasts (Iseki et al, 1997(Iseki et al, , 1999Rice et al, 2000). A recent elegant study using single cell RNA-seq analysis demonstrated that one of the most significant OF-associated genes is Col22a1, which encodes cross-linking extracellular matrix (ECM) collagen (Holmes et al, 2020).…”

“…frontal bone) is initiated at embryonic day (E) 12.5 when osteogenic precursors derived from cranial neural crest (CNC) cells spread upward to the top of the skull (Ishii et al, 2005;Noden and Trainor, 2005). Experimental evidence shows that growth factor signaling, such as fibroblast growth factor (FGF) and bone morphogenetic protein (BMP) signaling, controls osteogenic proliferation and differentiation (Iseki et al, 1997(Iseki et al, , 1999Kim et al, 1998;Komatsu and Mishina, 2016;Komatsu et al, 2013;Rice et al, 2000). These developmental processes occur at the unique niche between the cranial sutures and the edge of skull bones.…”