Discerning a Potential Link between MEMO1’s Role in Vascular, Bone, and Craniofacial Development

Abstract

Embryonic development of craniofacial structures requires the tight integration of multiple tissues and cell‐types. For example, the intersection of neural crest derived mesenchyme with mesoderm derived endothelium (i.e., vasculature) is necessary for craniofacial bone development and mineralization. Despite craniofacial anomalies being the 2nd leading congenital anomaly worldwide, our understanding of how these tissues interact is limited.Through a forward genetic screen, we previously identified a novel role for the protein encoded by the gene mediator of ERBB2‐driven cell motility 1 (Memo1) in craniofacial development. Global loss of Memo1 resulted in a range of defects, including hypo‐mineralization of the craniofacial skeleton, fully penetrant cleft secondary palate, coupled with widespread vascular abnormalities. Interestingly, while neural crest cell specific deletion of Memo1 recapitulated some aspects of global loss of Memo1, several defects were less apparent—suggesting MEMO1 functions in tissues outside the neural crest during craniofacial development. Further, molecular profiling of craniofacial elements in global Memo1mutants identified significantly altered Vegfa expression, coupled with disrupted vascular development, relative to controls. Based on these observations, along with Memo1’s semi‐ubiquitous expression during development, we hypothesized that MEMO1 functions within the endothelial derived vasculature and this function is necessary for proper craniofacial development.To test this hypothesis, we have generated a Memo1 endothelial specific mouse knock‐out model. Similar to Memo1 global knock‐outs, and in contrast to Memo1 neural crest knock‐outs and controls, Memo1 endothelial knock‐outs develop vascular hemorrhaging and edema with variable penetrance. Vascular defects are accompanied by gross alterations to craniofacial shape. We are currently utilizing µCT, cell sorting coupled with gene expression profiling, and ex vivo ‘sprouting’ assays to quantify the impact endothelial loss of Memo1 has on craniofacial bone development and mineralization, MEMO1’s molecular role in craniofacial endothelial cells, and MEMO1’s functional role in endothelial cells, respectively.Overall, in addition to MEMO1’s neural crest cell specific role, our findings extend MEMO1’s function into an additional cell‐type, endothelial cells, during craniofacial development. These data illuminate the molecular pathology for how disrupted neural crest or endothelial cells may lead to human craniofacial disorders.