Genetic, Tissue, and Anatomical Interactions in Mandibulofacial Dysmorphogenesis

PROJECT SUMMARY Anomalies of the face invariably require some type of therapy, corrective surgery, and close follow-up while imposing a financial and emotional burden on patients and their families. Although the analysis of human data is critical, human studies pose particular problems, not the least of which is that critical times of prenatal development are not available for study. This proposal aims to identify the developmental and molecular processes underlying mandibulofacial anomalies using mouse mutants that we identified by systematically searching the current contents of the International Mouse Phenotyping Consortium (IMPC) in response to NIH PAR-20-137 for phenotyping IMPC embryonic and perinatal lethal KO mouse lines. Micro- or retrognathia are the most common terms used to describe mandibular phenotypes in mandibulofacial dysostosis, yet the current lack of precision in diagnoses of mandibular dysmorphology does not critically consider the potentially distinct etiology of these conditions and their influence on potential sequelae of anomalies. Micrognathia describes a mandible that is absolutely reduced in size, indicating that the mandible is primarily affected, while retrognathia refers to a normally sized mandible that is placed posteriorly relative to the upper jaw. Thus, micrognathia and retrognathia, while providing similar facial profiles, are produced by different primary developmental processes and each may integrate differently with tongue and palatal development. When mandibular dysmorphology occurs with glossoptosis, respiratory obstruction, and in some cases, a cleft palate, the condition is referred to as Pierre Robin (PR). A causative pathogenesis of a sequence of developmental events has been hypothesized for PR, but few clear causal relationships between discovered mutations, dysregulated gene expression, precise cellular processes, and PR-associated anomalies are documented. To test this hypothesis, we plan a carefully coordinated and fully collaborative set of analyses of IMPC mutant mouse lines identified based on genes known to be causative for PR in humans or on the presence of PR features recorded in these mouse lines. Our in-depth phenotyping will involve: Aim 1: quantitative 3D morphologic analyses of embryos using phosphotungstic acid-enhanced micro computed tomography; Aim2: differential gene expression analysis of relevant tissues and developmental time points between mutant and unaffected littermate controls using bulk RNA-seq and spatial transcriptomics; Aim 3: histologic studies using in situ hybridization or immunohistochemistry of relevant genes, signaling pathways, cellular processes, and differentiation states to determine the cellular and molecular events giving rise to dysmorphogenesis of the mandibulofacial complex. This multi-level, systems biology approach will provide precise definitions of the localized effects of genetic variants on mandibular and associated tongue, palatal, and upper airway phenotypes to identify the developmental and molecular functions involved in their production, using mouse lines that model the phenotypes associated with these conditions.