The transcriptional cofactor MEIS2 as target of extrinsic inputs from the SVZ stem cell niche

• Applicant: Professorin Dr. Dorothea Schulte
• Subject Area: Developmental Neurobiology ; Molecular Biology and Physiology of Neurons and Glial Cells
• Term: from 2010 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 135372709

Adult neurogenesis is controlled by cell-intrinsic and -extrinsic factors. Yet, how extrinsic signals impinge on the activity of intrinsic regulators of cell fate is still largely unexplored. The present proposal aims at answering this question using the SVZ neurogenic niche of mice as model. The atypical homeo¬domain protein MEIS2 is present in the cell nuclei of newly generated neurons in the SVZ and functions as essential cofactor of the neurogenic transcription factor Pax6 in these cells (Agoston et al., 2014). Our unpublished results show that weak MEIS2 expression can already be found in undifferentiated progenitor cells, where it is uniformly distributed between cytoplasm and nucleus. By mass-spectrometry, we identified two posttranslational modifications (PTMs), a serine-phosphorylation and a mono-methylation on arginine, in MEIS2 isolated from neurons, which were not present on the corresponding amino acids in MEIS2 isolated from progenitor cells. This suggests that the activation and nuclear accumulation of MEIS2 at the onset of neuronal differentiation is controlled by PTMs. We could already gather initial data confirming this hypothesis for the arginine-methylation. In the current funding proposal I plan to extend on this finding. Specifically, I plan to address the following, more specific points: We will examine the functional relevance of the serine-phosphorylation in MEIS2 and investigate, by pharmacological, biochemical and genetic approaches combined with additional mass-spectrometry analyses, whether phosphorylation and methylation control MEIS2 activity in a combinatorial manner. We will further use similar approaches to investigate the intracellular pathway(s), which trigger MEIS2' modification in response to signals from the SVZ stem cell niche. Because methylation and phosphorylation of histones are important components of epigenetic gene expression control, we will also investigate whether MEIS2 is not only modified itself but also recruits the corresponding enzymes to the regulatory regions of neuron-specific genes. Finally, because MEIS proteins are known oncogenes in several forms of cancer, we will assess whether MEIS2 (or the related MEIS1) are posttranslationally modified in various cancer cell lines. We will also raise modification specific antibodies and use these to assess MEIS' posttranslational modification in different biological contexts, including different tumor entities. I expect two important outcomes from this research program: First, it will provide a significant step toward understanding how niche-derived, extrinsic cues impinge on transcrip¬tional regulators to control the rate of neuron production in the adult brain. Second, under¬standing in detail how MEIS activity is regulated posttranslationally may provide a starting point for novel approaches to target MEIS activity in disease.

• DFG Programme: Research Grants