Functional analysis of autism spectrum disorder-associated ubiquitin protein ligase E3C Ube3C in cortical development

• Applicant: Dr. Mateusz C. Ambrozkiewicz
• Subject Area: Developmental Neurobiology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 536563141

The central dogma of molecular biology states that a DNA-embedded code transcribed onto the mRNA comprises a template for protein synthesis. Beyond this genetic program, post-translational modifications (PTM) of proteins exponentially increase the molecular diversity of the proteome and account for different protein activities and fates. Ubiquitination is a reversible PTM catalyzed by E3 ligases and results in conjugation of ubiquitin molecule to the target protein. It is estimated that genes encoding for E3 ubiquitin ligases comprise 5% of the entire human genome. Of all E3 ligase genes, approximately 13% are directly linked to a neurological disorder. Among these, mutations in E3 ligase genes associated with autism spectrum disorder (ASD) form the biggest group. To date, the mechanistic characterization of ubiquitination cascade and its relevance to brain development remains underwhelming. In this proposal, we will investigate UBE3C, a ubiquitin ligase associated with ASD. Our preliminary data unveil that its murine ortholog, Ube3C, is indispensable for proper lamination of upper layer cortical neurons, thought to establish a biological substrate for higher cognitive functions of the cerebral cortex. Moreover, we find that UBE3C activity is associated with establishment of neuron-to-astrocyte ratio in the developing neocortex, indicative of its crucial functions in the cortical progenitors. Additionally, we discover Ube3C-mediated regulation of proteasome processivity in primary cortical cultures, implicating Ube3C in control of the proteome lifetime. Overall, we show that Ube3C is an important player in the development of the cerebral cortex. We propose a systematic experimental framework to uncover the Ube3C-driven molecular and cellular underpinnings of ASD-associated developmental processes. The approach outlines in vivo studies using Ube3C forebrain-specific knockout (KO) mouse model, that we recently established, multitude of advanced histological and imaging strategies, ubiquitination biochemistry and state-of-the-art transcriptomic and proteomic methods to identify the ubiquitination targets and molecular signaling orchestrated by the ligase. We propose to investigate the end-point consequences of Ube3C loss for cortical connectivity using a cutting-edge whole brain imaging technique. Using human induced pluripotent stem cells, we propose the use of brain organoids to elucidate the consequences of UBE3C loss for early human brain development. This study will grant mechanistic insights into the poorly characterized niche of ubiquitination biology related to cortical development, and novel aspects of the molecular and cellular pathology of ASD, offering a gateway for possible treatment strategies impinging on modulating activity of UBE3C.

• DFG Programme: Research Grants