26 - Navigating potholes in the road: mosaic deletion of fibronectin disrupts apical expansion of calvarial osteoblasts in frontal bone primordia

Poster Board Number: 26
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Co-authors:

Yifan Zhai, MS - Graduate student, Biology, Case Western Reserve Univ; Xioatian Feng - Case Western Reserve Univ; Radhika Atit, Ph.D. - Professor, Biology, Case Western Reserve Univ

Abstract Body : Improper formation of skull bones can lead to congenital birth defects such as calvarial dysplasias and craniosynostosis and skull bone fractures affecting 2.8 million Americans annually . Skull bones encase the brain and are formed through baso-apical expansion of calvarial osteoblasts. Fibronectin1 (FN1), an extracellular matrix protein and substrate, is broadly expressed in the mouse embryonic cranial mesenchyme containing the frontal bone primordia (FBP) and is known to mediate cell migration, adhesion and differentiation in various developmental contexts. We recently showed that conditional deletion of fibronectin in the cranial mesenchyme decreases apical expansion of the FBP. Alternatively, we propose a more subtle FN1 deletion model, known as mosaic deletion, to investigate if FN1 is actively used as a substrate for efficient apical expansion in the FBP. Thus, we hypothesize that if FN1 is the substrate for efficient apical expansion of frontal bone osteoblasts then mosaic deletion of fibronectin1 should decrease apical expansion of the frontal bone primordia. By using an inducible cranial mesenchyme CRE mouse line, we generated mosaic deletion and knockdown of Fn1 starting embryonic day (E) 10.0. Here, we show mosaic deletion of FN1 and knockdown model causes diminished expansion of FBP at E12.5 and E13.5. At the cellular level, mosaic deletion of FN1 leads to fewer osteoblasts expanding into the apical region of the FBP at both E12.5 and E13.5. We found cellular elongation of calvarial osteoblasts is diminished, underlying the tissue level effect at E12.5 and E13.5. Interestingly, calvarial osteoblasts elongate to migrate around the regions or “holes” lacking FN1 expression in the cranial mesenchyme. However, this cellular behavior is not sufficient to compensate for the mosaic deletion and still causes an overall diminished expansion of the FBP. Thus, mosaic deletion of FN1 provides evidence towards a new mechanism of calvarial growth and calvarial dysplasias.