Functional consequences of Satb2 monoubiquitination in the developing neocortex

• Applicants: Dr. Mateusz C. Ambrozkiewicz; Professor Dr. Victor Tarabykin
• Subject Area: Developmental Neurobiology ; Cell Biology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 515247130

Establishment of brain connectivity requires a concerted sequence of cellular and molecular transitions. The development of upper cortical layers and their projections is determined by a transcription factor Special AT-Rich Sequence Binding 2, SATB2. Inactivating mutations in SATB2 gene lead to a severe systemic developmental disorder, called SATB2-Associated Syndrome, characterized by intellectual disability with absent or limited language skills and behavioral problems. Loss of murine ortholog Satb2 leads to agenesis of corpus callosum, ectopic expression of deep layer markers in projection neurons of upper cortical layers, neuronal migration arrest and behavioral aberrances. A great deal of work addressed the downstream targets of Satb2, however, its upstream modulators have remained largely uncharted. Our preliminary findings elucidate that nuclear expression of Satb2, predicted from its function as a transcription factor, is developmentally regulated. In the early stages of cortical development, Satb2 protein is found in the cytoplasm or cortical cells. We also show that cytoplasm-localized Satb2 is monoubiquitinated and that this post-translational modification hinders its nuclear entry. In this proposal, we aim to identify E3 ubiquitin ligases and deubiquitinating enzymes that modify Satb2 and thereby enable its nuclear expression ergo function as a transcription factor. We aim to utilize Satb2 mouse lines and in utero electroporation, as well as state-of-the-art biochemical and cell biological experiments to delineate the ubiquitination cascades upstream of Satb2 in the cortex that regulate the development of the main axonal tract in the placental mammals, the corpus callosum. We will also investigate a possibility of another, transcription factor-independent role of Satb2 in the cytoplasm of developing progenitors using Fucci2aR reporter mouse lines. Our study will reveal a novel layer of regulation of Satb2 and thereby unveil new modes of post-transcriptional gene expression regulation in the developing neocortex. Additionally, this project will extend our understanding of the consequences of protein ubiquitination in cells.

• DFG Programme: Research Grants