Orofacial clefts are one of the most common birth defects in the U.S., occurring in 1/750 live births. The lifetime cost for medical treatment, educational services and lost productivity averages more than $100,000 per affected person. While the majority of orofacial clefts result in cleft lip with or without cleft palate (CL/P), a small percentage results in oblique facial clefts (ObFC) that extend from the oral cavity to the eye. Although less common, insights into the cellular mechanism of ObFC - first definitively classified by Paul Tessier in 1976 - have remained elusive. We have identified two de novo occurrences of SPECC1L mutations in patients with ObFC. Our studies in zebrafish and fly provide significant insight into SPECC1L function, which thus far had remained unstudied with no scientific publications. Knockdown of a previously uncharacterized zebrafish SPECC1L homolog perturbs cranial neural crest (CNC) and results in a dramafic loss of facial structures, thus extending SPECC1L function in facial morphogenesis to other vertebrates. In addition, knockdown of the sole uncharacterized Drosophila ortholog phenocopies - to an extraordinary extent - known fly mutants in the integrin-signaling pathway that exhibit cell adhesion and migration defects. Furthermore, our cellular and molecular analyses show that SPECC1L is a novel cytoskeletal cross-linking protein that interacts with both the microtubule and actin cytoskeletons. Transient expression of SPECC1LGFP stabilizes a subset of microtubules, while SPECC1L knockdown causes defective actin cytoskeleton reorganization and impairs cell adhesion and migration. Together with mouse Speed I expression in the developing facial prominences, these results begin to explain how human ObFC can arise following SPECC1L deficiency.
The aim of this proposal is to develop a mouse model to test the pathogenetic mechanism of SPECC1L deficiency in mammalian facial morphogenesis (Aim 1) and to precisely define the cellular (Aim 2) and molecular (Aim 3) role of SPECC1L in CNC cell migration and specification of facial structures.
Insights into the cellular and molecular mechanism of oblique facial clefts (ObFC) - that extend from the oral cavity to the eye - have remained elusive. We have identified the first gene, SPECC1L, mutated in patients with ObFC and this proposal aims to define the cellular and molecular role of SPECC1L in mammalian facial morphogenesis using a mouse model.
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