Date of Award

5-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Genetics

Committee Member

Dr. Anand K. Srivastava, Committee Chair

Committee Member

Dr. Chin-Fu Chen

Committee Member

Dr. James Morris

Committee Member

Dr. Michael Sehorn

Committee Member

Dr. Liangjiang Wang

Abstract

Autism spectrum disorders (ASD) and intellectual disability (ID) are the two most frequently reported, often co-morbid, neurodevelopmental disorders that affect children all over the world. Previously, a genetic association of the ZBTB20 gene, located at chromosome 3q13.2, with ASD and ID was identified. The gene is highly expressed in developing brain and encodes two isoforms of 668- (short isoform) and 741- (long isoform) amino acid proteins that belong to the BTB (broad complex, tramtrack, bric-a-brac) – zinc finger family of transcription factors. The human ZBTB20 protein was functionally characterized using various molecular and cellular approaches, to elucidate its contribution to ASD and ID.ZBTB20 is primarily localized in the nucleus, the short and long isoforms of ZBTB20 form homodimers and heterodimers. The N-terminal region of ZBTB20that includes the BTB domain appears to be critical for dimerization. A ZBTB20 yeast two-hybrid screen was performed using human fetal brain cDNA library, to determine its function in neuronal cells. Several brain-expressed proteins that interact with ZBTB20, including the E2 SUMO conjugating enzyme UBC9 were identified. Moreover, ZBTB20 contains two putative conserved SUMOylation (ΨKXE) motifs. The ZBTB20 protein undergoes SUMOylation, binds SUMO1, and the N-terminal region of ZBTB20 is critical for its interaction with UBC9. The ZBTB20 K330 residue in SUMOylation motif 1 is the likely target for in vivoSUMOylation. Altering residue K330 had no effect on ZBTB20 subcellular localization, stability or repression activity, but interfered with its dimerization. Consistent with studies in mice, ZBTB20 functions as a transcriptional repressor. Overexpression of wild type ZBTB20, but not the ASD/ID-associated ZBTB20mutants in HEK293H cells resulted in significantly reduced expression of transcription factor genes MEF2C, TBR1 and FEZF2, previously shown to be associated with ASD and ID. These results suggest a potential contribution of a ZBTB20-dependent transcription regulation mechanism in neurodevelopmental disorders such as ASD and ID.

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