Cranial Neural Crest Cell Susceptibility to Oxidative Stress and Apoptosis: Implications for SMCHD1-mediated Bosma Arhinia Microphthalmia Syndrome

Neural crest cells (NCC) and cranial placodes are transient cell populations that arise early in embryonic development at the boundary of the neural and non-neural ectoderm. NCC delaminate from the neuroectodermal border and differentiate into diverse cell types, while cranial placode cells differentiate into distinct sensory placodes. Bosma arhinia microphthalmia syndrome (BAMS) is caused by mutations in the epigenetic repressor, SMCHD1, and is defined by a triad of arhinia (absent external nose), ocular defects, and hypogonadism. We hypothesize that BAMS is a neurocristopathy, a disorder of NCC, because cranial NCC give rise to the nasal, ocular, and neuro-reproductive systems. Survival and migration of placode cells depends on cues from NCC, and thus BAMS likely represents a defect in NCC and/or placode cell proliferation, migration and/or terminal differentiation.Facial structure development results from programmed apoptosis of NCC as they migrate into the craniofacial mesenchyme. NCC may be particularly sensitive to apoptotic signals from oxidative stress, which can be induced by defects in metabolic processes. We propose that mutations in SMCHD1 increase NCC susceptibility to oxidative stress and induce defects in apoptosis, culminating in facial structure abnormalities. Furthermore, we posit that SMCHD1 dysfunction may render NCC less responsive to metabolic regulation of oxidative stress and apoptosis.We created gene expression profiles with O9-1 cells, a murine NCC line, using RT-PCR. We found that manipulating glucose conditions had an impact on NCC physiology culminating in the loss of NCC and stem cell characteristics, reduced antioxidant gene expression, and a propensity to differentiate into bone rather than skeletal muscle in high glucose (25 mM) conditions. Additionally, Smchd1 knockdown cells are less NCC-like, may be halted in an undifferentiated state, and may be more likely to differentiate into cartilage and smooth muscle cells. Smchd1 knock-down also results in higher expression of oxidative stress genes and a dysregulation of apoptosis gene transcription.Future experiments will compare these effects in wild-type vs Smchd1 knockout cells, as well cells expressing point-mutant versions of SMCHD1. Studying NCC in this context will not only aid in elucidating the molecular mechanisms underlying BAMS, but will also provide insights into NCC physiology, allowing for the discovery of potential druggable targets in the prevention of neurocristopathies, as well as in the development of tissue regeneration technologies.Bachelor of Scienc