Characterizing the role of Pdgfra in calvarial development.

BACKGROUND: Mammalian calvarium is composed of flat bones developed from two origins, neural crest, and mesoderm. Cells from both origins exhibit similar behavior but express distinct transcriptomes. It is intriguing to ask whether genes shared by both origins play similar or distinct roles in development. In the present study, we have examined the role of Pdgfra, which is expressed in both neural crest and mesoderm, in specific lineages during calvarial development. RESULTS: We found that in calvarial progenitor cells, Pdgfra is needed to maintain normal proliferation and migration of neural crest cells but only proliferation of mesoderm cells. Later in calvarial osteoblasts, we found that Pdgfra is necessary for both proliferation and differentiation of neural crest-derived cells, but not for differentiation of mesoderm-derived cells. We also examined the potential interaction between Pdgfra and other signaling pathway involved in calvarial osteoblasts but did not identify significant alteration of Wnt or Hh signaling activity in Pdgfra genetic models. CONCLUSIONS: Pdgfra is required for normal calvarial development in both neural crest cells and mesoderm cells, but these lineages exhibit distinct responses to alteration of Pdgfra activity.

Deregulated Rac1 Activity in Neural Crest Controls Cell Proliferation, Migration and Differentiation During Midbrain Development.

Mutations in RAC1 allele are implicated in multiple brain tumors, indicating a rigorous control of Rac1 activity is required for neural tissue normal development and homeostasis. To understand how elevated Rac1 activity affects neural crest cells (NCCs) development, we have generated Rac1 CA ;Wnt1-Cre2 mice, in which a constitutively active Rac1 G12V mutant is expressed specifically in NCCs derivatives. Our results revealed that augmented Rac1 activity leads to enlarged midbrain and altered cell density, accompanied by increased NCCs proliferation rate and misrouted cell migration. Interestingly, our experimental data also showed that elevated Rac1 activity in NCCs disrupts regionalization of dopaminergic neuron progenitors in the ventral midbrain and impairs their differentiation. These findings shed light on the mechanisms of RAC1 mutation correlated brain tumor at the cellular and molecular level.

Pdgfra regulates multipotent cell differentiation towards chondrocytes via inhibiting Wnt9a/beta-catenin pathway during chondrocranial cartilage development.

The mammalian skull is composed of the calvarial bones and cartilages. Malformation of craniofacial cartilage has been identified in multiple human syndromes. However, the mechanisms of their development remain largely unknown. In the present study, we identified Pdgfra as a novel player of chondrocranial cartilage development. Our data show that Pdgfra is required for normal chondrocranial cartilage development. Using tissue-specific genetic tools, we demonstrated that Pdgfra is essential for chondrocyte progenitors formation, but not in mature chondrocytes. Further analysis revealed that Pdgfra regulates chondrocytes progenitors development at two stages: in embryonic mesenchymal stem cells (eMSCs), Pdgfra directs their differentiation toward chondrocyte progenitors; in chondrocytes progenitors, Pdgfra activation promotes cell proliferation. We also found that excessive Pdgfra activity causes ectopic cartilage formation. Our data show that Pdgfra directs eMSCs differentiation via inhibiting Wnt9a transcription and its downstream signaling, and activating Wnt signaling rescues ectopic cartilage phenotype caused by excessive Pdgfra activity. In summary, our study dissected the role of Pdgfra signaling in chondrocranial cartilage formation, and illustrated the underlying mechanisms at multiple stages.

Expression pattern of Kmt2d in murine craniofacial tissues.

Formation of the calvaria is a multi-staged process and is regulated by multiple genetic factors. Disruption of normal calvarial development usually causes craniosynostosis, a prevalent birth defect characterized by premature fusion of calvarial bone. Recent studies have identified mutations of KMT2D allele in patients with craniosynostosis, indicating a potential role for Kmt2d in calvarial development. KMT2D mutations have also been implicated in Kabuki syndrome, which features a distinct facial appearance, skeletal abnormality, growth retardation and intellectual disability. However, the expression pattern of Kmt2d has not been fully elucidated. In the present study we examined the expression pattern of Kmt2d at multiple stages of embryo development in mice, with a focus on the craniofacial tissues. Our in situ hybridization results showed that Kmt2d mRNA is expressed in the developing calvarial osteoblasts, epithelia and neural tissues. Such an expression pattern is in line with the phenotypes of Kabuki syndrome, suggesting that Kmt2d plays an intrinsic role in normal development and homeostasis of these craniofacial tissues.