Phosphorylation of Msx1 promotes cell proliferation through the Fgf9/18-MAPK signaling pathway during embryonic limb development

Abstract

Msh homeobox (Msx) is a subclass of homeobox transcriptional regulators that control cell lineage development, including the early stage of vertebrate limb development, although the underlying mechanisms are not clear. Here, we demonstrate that Msx1 promotes the proliferation of myoblasts and mesenchymal stem cells (MSCs) by enhancing mitogen-activated protein kinase (MAPK) signaling. Msx1 directly binds to and upregulates the expression of fibroblast growth factor 9 (Fgf9) and Fgf18. Accordingly, knockdown or antibody neutralization of Fgf9/18 inhibits Msx1-activated extracellular signal-regulated kinase 1/2 (Erk1/2) phosphorylation. Mechanistically, we determined that the phosphorylation of Msx1 at Ser136 is critical for enhancing Fgf9 and Fgf18 expression and cell proliferation, and cyclin-dependent kinase 1 (CDK1) is apparently responsible for Ser136 phosphorylation. Furthermore, mesenchymal deletion of Msx1/2 results in decreased Fgf9 and Fgf18 expression and Erk1/2 phosphorylation, which leads to serious defects in limb development in mice. Collectively, our findings established an important function of the Msx1-Fgf-MAPK signaling axis in promoting cell proliferation, thus providing a new mechanistic insight into limb development.

Genome-Wide CRISPR/Cas9-Based Screening for Deubiquitinase Subfamily Identifies Ubiquitin-Specific Protease 11 as a Novel Regulator of Osteogenic Differentiation

“…The MSX family gene is essential during embryogenesis and early development of limbs and craniofacial tissues, including teeth and bone [7,33]. MSX1 is transiently expressed in undifferentiated precursor cells, undergoes downregulation upon terminal differentiation, and exhibits a vital role in skeletal muscle development and bone remodeling [38,39].…”

“…For instance, the cyclin-dependent kinase 1 (CDK1)-mediated phosphorylation of Msx1 at Ser136 is critical for enhancing Fgf9 and Fgf18 expression responsible for normal cell proliferation during early limb development. Depletion of Msx1/2 results in the downregulation of Fgf9 and Fgf18 expression and Erk1/2 phosphorylation, which leads to serious defects in limb development in mice [7].…”

“…Transgenic mice with alpha (I) collagen promoter-regulated Msx1 expression also showed an increased proportion of osteoblasts, including enhanced proliferation and apoptosis, suggesting the critical role of Msx1 in craniofacial bone modeling [5]. The controlled and timely expression of the MSX1 gene is necessary for normal osteogenesis, craniofacial development, and limb-pattern formation [5][6][7]. Mutations in Msx1 have been linked to craniofacial defects and tooth agenesis in mice [8,9], while genetic alterations in human MSX1 are associated with cleft lip/palate and tooth agenesis [5,6,[10][11][12].…”

“…PTMs such as SUMOylation, phosphorylation, and ubiquitination play critical roles in vital cellular processes, such as proliferation and differentiation in bone homeostasis [14][15][16][17]. A recent study reported that during embryonic limb development, the phosphorylation of Msx1 promotes cell proliferation through the Fibroblast growth factor 9/18-Mitogen-activated protein kinase (Fgf9/18-MAPK) signaling pathway [7]. In the past few years, extensive research has focused on elucidating the importance of the ubiquitin-proteasome system (UPS) in the regulation of osteogenesis and bone development [18,19].…”

Multi-Omics Analysis in β-Thalassemia Using an HBB Gene-Knockout Human Erythroid Progenitor Cell Model

“…Cell viability was measured by trypan blue staining following the manufacturer’s instructions (Abcam, Cambridge, UK). The cell cycle assay was performed as previously described [ 44 ]. Briefly, HUDEP2 HBB-KO and HUDEP2 WT cells were washed with PBS, resuspended in PBS containing Triton X-100 (3‰) (Sigma, Kawasaki, Japan), propidium iodide (10 mg/mL) Sigma, Kawasaki, Japan, and Rnase A (50 μg/mL) (Novoprotein, Shanghai, China), then incubated in the dark for 15 min.…”