Unique and intertwined functions of AUTS2 isoforms in brain development and behavior

Rearrangements within the AUTS2 region are associated with a rare syndromic disorder with intellectual disability, developmental delay and behavioral abnormalities as core features. In addition, smaller regional variants are linked to wide range of neuropsychiatric disorders, underscoring the gene’s essential role in brain development. Like many essential neurodevelopmental genes, AUTS2 is large and complex, generating distinct long (AUTS2-l) and short (AUTS2-s) protein isoforms from alternative promoters. Although evidence suggests unique isoform functions, the contributions of each isoform to specific AUTS2-linked phenotypes have not been clearly resolved. Furthermore, Auts2 is widely expressed across the developing brain, but cell populations most central to disease presentation have not been determined. To understand the specific roles of AUTS2-l in brain development, we focused on brain pathology, behavior, and postnatal brain gene expression, showing that brain-wide AUTS2-l ablation leads to specific subsets of the recessive pathologies associated with C-terminal mutations that disrupt both isoforms. We identified downstream genes that could explain expressed phenotypes including hundreds of putative direct AUTS2- l target genes. Furthermore, in contrast to C-terminal Auts2 mutations which lead to dominant hypoactivity, AUTS2-l loss-of-function is associated with dominant hyperactivity, a phenotype exhibited by many human patients. Finally, we showed that AUTS2-l ablation in Calbindin 1-expressing cell lineages is sufficient to yield learning/memory deficits and hyperactivity with abnormal dentate gyrus granule cell maturation, but not other phenotypic effects. These data provide new clues to in vivo AUTS2-l functions and novel information relevant to genotype-phenotype correlations in the human AUTS2 region. In addition, AUTS-l is shown to regulate neuron development via its nuclear function in chromatin structure and gene regulation. For example, AUTS2-l is shown to engage in both activating complex AUTS2-PRC1 and repressive complex NuRD. To understand effect of AUTS2-l ablation on chromatin structure, and to correlate chromatin changes with gene expression, cooperative interaction with brain TFs, and downstream TF binding, we examined AUTS2-l LOF mutant brain and compared to WT controls. We proposed an alternative model of AUTS2 action, where AUTS2 regulates neuronal gene expression through modulating both the availability and the efficiency of chromatin binding of downstream TFs at their target sites by opening up distal enhancer sites for TFs to bind, including both repressive and activating kinds. Lastly, we described a novel Auts2-exon 9 mutation in aspects of brain development, behavior, and chromatin and gene expression pattern. We identified distinct behavioral and brain development phenotypes involving key AUTS2-linked phenotypes such as learning and memory defects, social deficits, and brain development abnormalities involving cell maturation and dendritic and axon development. Together these data would lay foundation for direct comparison between Auts2 N-terminal and C-terminal mutations and identifying genotype:phenotype relationships in AUTS2-linked diseases. Together, this thesis provides critical insights on AUTS2 isoform specific functions in developing brain, explores which cell types are most central to AUTS2-linked phenotypes, depicts genotype:phenotype relationships in this genetic region, as well as proposing AUTS2 mechanism of action at molecular level. Our data advance the understanding of this important gene that’s central to basic neuronal development process as well as to a wide range of neurodevelopmental and neuropsychiatric diseases.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Cell and Developmental Biology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Song, Yunshu

Contributors dc:contributor

• Stubbs, Lisa
• Chen, Jie
• Ceman, Stephanie
• Raetzman, Lori

• Auts2
• Genetic
• Developmental Biology

Statement dc:rights

• We need this thesis to be embargoed for the longest option of years.

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/122214

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F122214