Dr. Susan Perrine

Associate Research Professor

Department:  Anthropology
College:  College of Liberal Arts
Address:  320 Carpenter Bldg
E-mail: qzk2@psu.edu
Website: https://getahead.la.psu.edu/

SkeMA Lab (Skeletal Morphogenetics Analysis Lab)
Genetic, Tissue, and Anatomical Interactions in Mandibulofacial Dysmorphogenesis
Mandibulofacial anomalies are common birth defects that require comprehensive, sometimes repetitive corrective surgeries to manage individual cases, often placing a heavy financial and emotional burden on patients and their families. Development of therapeutic efforts requires a thorough understanding of craniofacial development and the timing of events in dysmorphogenesis. We offer innovative approaches for determining the molecular, cellular, and developmental bases of mandibulofacial morphogenesis critical to craniofacial development, in normal individuals and in craniofacial conditions such as Pierre Robin.

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.

 

Cartilage and bone of the lower jaw in development and disease
Mandibular anomalies are common birth defects that require comprehensive, sometimes repetitive corrective surgeries to manage individual cases, often placing a heavy financial and emotional burden on patients and their families. Development of therapeutic efforts requires a thorough understanding of mandibular development and the timing of events in dysmorphogenesis. We offer innovative approaches for determining the molecular, cellular, and developmental bases of morphogenesis of the mandible and its cartilaginous precursor, Meckel’s cartilage, in normal individuals and in craniofacial conditions with a small mandible.

The lower jaw evolved as a structure composed of many bones the largest of which, the dentary, persists as a single lower jawbone in modern mammals, and is referred to as the mandible in humans. Mandibular disorders, often resulting in small jaws, are among the most common human birth defects. These disorders can dramatically affect quality of life, and are often associated, or compound problems with airway obstruction, speech, and feeding. During embryogenesis, development of the mandible is preceded by and associated with a tubular cartilage rod called Meckel’s cartilage (MC) and anomalies of MC have been associated with mandibular disorders. Development of MC in modern mammals is complex: the anterior part contributes to the formation of the mandibular symphysis, its posterior part forms cartilages that mineralize endochondrally to form two middle ear bones, and the posterior half of the middle region forms ligaments. Less is known about the anterior half of the middle region of MC, which is transient, present during a small window of embryonic development before it disappears. Established assessments describe MC as a template for the formation of the mandible, but evidence of this is lacking and little is known of the relationship between the midportion of MC and mandibular mineralization, size, and shape or the processes of MC growth in length, perichondrial ossification, and disappearance of MC. We present data demonstrating that MC does not serve as a template in the way cartilaginous models function in endochondral ossification and hypothesize a new role for the mid portion of MC in determining mandibular length, mineralization of the perichondrium, mineralization of the mandible, and its disappearance. Because our findings challenge the traditional role of MC, we have designed this project to validate the developmental events that take place as the midportion of MC disappears and the mandible forms through a detailed analysis of four processes: 1) initiation and growth in length of MC; 2) mineralization of MC perichondrium; 3) mineralization of the mandible; and 4) disappearance of MC. Our approach is based on knowledge we have gained through preliminary investigations of these processes occurring at different times along the length of MC, and spanning the buccal to lingual aspects of the interior of MC. We couple 3D imaging with tissue and cellular analyses of embryonic mutant Sox9flox/flox;Col2a1-CreERT, and Sox9flox/flox mice to precisely define the changing cellular dynamics of the lower jaw in developmental time and anatomical space. These data are used in turn to inform our RNA-seq analyses of the developing MC and mandible directed at recovering the underlying transcriptome by differential gene expression, pathway, and network analyses. We plan cell lineage tracing experiments to determine the fate of cells from the intermediate region of MC, those that initiate MC perichondrial mineralization, and mandible mineralization. Our integrative approach is designed to bring new understanding to lower jaw development and open novel research areas to advance strategies for bone repair, regeneration, and prevention in mandibular disease.