Molecular mechanisms of tissue interactions during coronal suture development

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The overall objective in this application is to examine the fundamental mechanisms underlying coronal suture development. We will test the central hypothesis that tissue interaction between tectum transversum (TTR) and coronal sutures interact during development, and a rigorous regulation of Pdgfra activity is required for their interaction. Pdgfra plays a crucial role in craniofacial development, and elevated PDGFRA expression and activity is implicated in human craniosynostosis. We will examine the following specific aims: 1. To examine interaction between TTR and suture cells during embryonic development. In this aim we will test the hypothesis that TTR and suture cells interact during embryogenesis. In aim 1a, we will examine the coronal suture development with removal of TTR. In aim 1b, we will assess the requirement of coronal sutures on TTR development. We will use genetic tools to ablate coronal sutures specifically and assess TTR development in mouse models. 2. To examine the mechanisms underlying Pdgfra regulation on TTR development. The regulatory mechanisms underlying TTR development has not been illustrated. Alteration of Pdgfra activity causes distinct TTR phenotype, indicating Pdgfra is a critical player in TTR formation. By transcriptome profiling we identified Wnt9a and Sox9 as transcriptional targets of Pdgfra. In this aim we will test the hypothesis that Pdgfra regulates chondrocyte progenitors formation by regulating Sox9 expression via Wnt9a/beta-catenin signaling. In aim 2a, we will characterize the role of Pdgfra in TTR development, by analyzing the TTR phenotype in both Pdgfra loss-of-function (LOF) and gain-of-function (GOF) models. In aim 2b, we will analyze the role of Pdgfra in controlling chondrocyte progenitor formation. In aim 2c, we will examine Wnt9a/beta-catenin pathway as a potential mediator of Pdgfra in controlling Sox9 expression and chondrocyte progenitor formation. 3. To examine the role of Pdgfra in coronal sutural cells development and maintenance. It has been shown that suture contains abundant mesenchymal stem cells (MSCs). Pdgfra is a recognized MSCs marker. Our data show that Pdgfra is expressed in the developing suture. Constitutive activation of Pdgfra leads to abnormal differentiation in the developing sutures. In aim 3a, we will trace the suture progenitor cells in both Pdgfra LOF and GOF models by manipulating Pdgfra activity in a tissue-specific manner. In aim 3b, we will examine the role for Pdgfra in adult suture MSCs maintenance and their homeostasis using calvarial injury model. By completion of the proposed study, we expect to answer whether tissue interaction between TTR and coronal suture is essential for normal suture development, and what is the specific role for Pdgfra in normal suture development and craniosynostosis formation.