Research
Receptor tyrosine kinases (RTKs) bind to growth factors at the cell surface and activate various intracellular signaling pathways to elicit responses with broad roles in developmental cellular processes. A subset of RTK families has been shown to regulate the activity of neural crest cells (NCCs) and the development of their derivatives in mammalian systems. NCCs are migratory, multipotent cells that play a critical role in vertebrate development. Cranial NCCs originate from the forebrain to the hindbrain and populate the frontonasal prominence and pharyngeal arches 1-4. These cells give rise to the bone and cartilage of the frontonasal skeleton, among other derivatives.
Our lab is focused on investigating the mechanism and function of signaling through a particular RTK family, the platelet-derived growth factor (PDGF) receptor family, in development of the cranial NCC-derived craniofacial skeleton. Craniofacial development is a complex morphogenetic process, disruptions in which result in highly prevalent human birth defects. Signaling through the PDGFRs plays a critical role in this process in both humans and mice. Pdgfra mutant mouse models display a range of craniofacial phenotypes such as midline clefting, subepidermal blebbing and hemorrhaging. Functional analysis of PDGFRalpha signaling during mouse development has revealed roles in promoting migration of cranial NCCs, proliferation of the NCC-derived craniofacial mesenchyme and osteoblast differentiation. We have demonstrated a role for the other RTK in this family, PDGFRbeta, in murine craniofacial development, demonstrating that ablation of Pdgfrb in the NCC lineage results in increased nasal septum width, delayed palatal shelf development and subepidermal blebbing. Further, we showed that PDGFRalpha and PDGFRbeta genetically and physically interact in the craniofacial mesenchyme to form functional heterodimers with unique signaling properties, thus uncovering a novel mode of signaling for the PDGF family during vertebrate development.
Our lab is focused on investigating the mechanism and function of signaling through a particular RTK family, the platelet-derived growth factor (PDGF) receptor family, in development of the cranial NCC-derived craniofacial skeleton. Craniofacial development is a complex morphogenetic process, disruptions in which result in highly prevalent human birth defects. Signaling through the PDGFRs plays a critical role in this process in both humans and mice. Pdgfra mutant mouse models display a range of craniofacial phenotypes such as midline clefting, subepidermal blebbing and hemorrhaging. Functional analysis of PDGFRalpha signaling during mouse development has revealed roles in promoting migration of cranial NCCs, proliferation of the NCC-derived craniofacial mesenchyme and osteoblast differentiation. We have demonstrated a role for the other RTK in this family, PDGFRbeta, in murine craniofacial development, demonstrating that ablation of Pdgfrb in the NCC lineage results in increased nasal septum width, delayed palatal shelf development and subepidermal blebbing. Further, we showed that PDGFRalpha and PDGFRbeta genetically and physically interact in the craniofacial mesenchyme to form functional heterodimers with unique signaling properties, thus uncovering a novel mode of signaling for the PDGF family during vertebrate development.
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Our goal is to characterize novel intracellular pathways and cellular processes engaged downstream of PDGFR induction. We have several ongoing projects in the lab, each of which will provide significant insight into the mechanisms underlying mammalian craniofacial development and new therapeutic directions for the treatment of human craniofacial birth defects.
1. Exploring how Pdgfra and Pdgfrb genetically interact in the mouse NCC lineage to regulate migration and proliferation through conditional mutagenesis in the embryo followed by detailed phenotypic analyses as well as in vitro primary cell activity assays.
2. Examining the in vivo dynamics of PDGFR dimer formation in the craniofacial mesenchyme through bimolecular fluorescence complementation (BiFC). Relatedly, characterizing PDGFR dimer-specific interactomes through two approaches: a) genetic epistasis experiments between Pdgfra mutant mice and both null or constitutively active alleles of the gene encoding SHP-2, a protein which is critical for proper craniofacial development and which is differentially engaged in response to PDGFRalpha homodimer versus PDGFRalpha/beta heterodimer formation; b) coupling BiFC with affinity purification and mass spectrometry analysis to identify PDGFR dimer-specific interacting proteins.
3. Determining how the activity of RNA-binding proteins (RBPs) is regulated by PDGFRalpha signaling to generate protein isoforms necessary for midface development. The first part of this project employs biochemical techniques to determine the effects of PI3K/Akt-mediated phosphorylation of these RBPs downstream of PDGFRalpha signaling on their subcellular localization, RNA-binding and sequence specificity. The second part of this project will characterize the role of these RBPs during craniofacial development in vivo through phenotypic analyses of conditional knock-out and phosphomutant genetic models as well as next-generation sequencing to identify target transcripts in the facial mesenchyme.
