Investigating the Role of SWI/SNF Complex Proteins SMARCC1 and SMARCA4 in Regulating SIX-Family Transcriptional Activity

• Bryan Lehmann, Biological Sciences, University of Delaware

• Andre Luiz Pasqua Tavares, Biological Sciences, University of Delaware
• Gabriel DaSilva DaSilva, Biological Sciences, University of Delaware

Approximately 75% of craniofacial conditions have underlying genetic causes, most of which have yet to be discovered. Pathogenic variants in genes coding for SIX-family transcription factors and their interacting partners have been linked to several of these conditions, such as branchio-oto-renal syndrome (BOR), and holoprosencephaly 2 (HPE2). A hallmark of many SIX-family transcription factors is their interaction with protein partners to activate or repress target gene expression. Multiple experimental approaches have identified novel interacting partners for SIX1 and SIX3. A recent yeast two-hybrid screen predicted a potential interaction between SIX3 and SMARCC1. In addition, a published co-immunoprecipitation assay demonstrated an interaction between SIX1and SMARCA4. SMARCC1 and SMARCA4 are both members of the SWI/SNF chromatin remodeling complex, which regulate gene expression. We hypothesize that both SMARCA4 and SMARCC1 interact with SIX1 and SIX3 to alter their transcriptional activity. Plasmids containing SMARCA4 and SMARCC1 were successfully constructed using Gibson Assembly. Luciferase reporter assays were used to measure changes in transcriptional activity by transfecting SMARC-family genes into HEK293T cells. Additionally, immunohistochemistry illustrated co-localization of SIX3 and SMARCC1 within the developing eye, and SIX1 and SMARCC1 in the supraorbital mesenchyme (SOM) and mandibular arch. By determining whether SMARCC1 and SMARCA4

modulate SIX-family transcriptional activity, our work is identifying novel candidate genes that

may contribute to unresolved cases of craniofacial birth defects, including BOR and HPE2.

These findings provide a foundation for future studies investigating the pathogenic roles of these

chromatin-remodeling factors in craniofacial development and disease.