Mesenchymal condensation sets the stage for intramembranous bone development

Mesenchymal condensation is one of the earliest, and most critical, stages in the formation of intramembranous (directly ossifying) bone. It is during the condensation phase that key skeletogenic genes are first upregulated and during which collagen I, the scaffold on which the inorganic portion of bone will be deposited, is first established. Thus, morphogenesis and tissue specific gene expression occur concurrently. Previously, we used microarray analysis and in situ hybridisation to determine which genes are important and at what stage of development these genes act during intramembranous ossification in chick and zebrafish. In the current study, we utilize a combination of light and electron microscopy to better understand the patterning and polarization of cells in early skeletogenic condensations. We compare neural crest derived intramembranous bones, specifically the scleral ossicles of the chick ( Gallus gallus ) and the opercula of the zebrafish ( Danio rerio ). While our preliminary results in the chick suggest osteoblasts are polarized toward the center of the early condensations, more data is required to make a solid conclusion. Data collection in zebrafish is also ongoing. Combined, these studies provide a means to correlate gene expression and morphogenesis during intramembranous bone formation. Grant Funding Source : Nova Scotia Health Research Foundation (Canada) ; Natural Sciences and Engineering Research Council of Canada