Project Details
Projekt
Failure in PP2A/mTOR signaling, local protein synthesis and its consequences on functional connectivity in neurons from patients with Opitz BBB/G syndrome
Subject Area
Molecular Biology and Physiology of Neurons and Glial Cells
Term
from 2015 to 2018
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 279648055
Opitz BBB/G syndrome (OS) is a monogenic disorder that mainly affects ventral midline structures. Neurological characteristics include intellectual disability and mental developmental delay. OS syndrome is caused by mutations in the MID1 protein, which has been shown to mediate ubiquitin specific modification and degradation of the microtubule-associated catalytic subunit of protein phosphatase 2A (PP2Ac). Mutations as found in OS patients lead to an accumulation of PP2Ac and a hypophosphorylation of microtubule-associated proteins. By counteracting mTOR kinase PP2A is an important player in the regulation of local protein synthesis in synaptic compartments, which is the basis for long term potentiation, learning and memory. Dysregulation of the mTOR/PP2A axis is the underlying molecular mechanisms of several intellectual disability syndromes including Down syndrome, fragile-X syndrome and RETT syndrome. OS, the MID1 protein and its influence on neuronal function and connectivity can teach us much about local protein synthesis and mTOR/PP2A function on one side and its implications on cognitive (mal-) functions in mouse and man on the other. In a mouse model carrying a full knock-out of the OS responsible gene, Mid1, a pronounced defect in axonal outgrowth was shown. While axonal outgrowth deficiency can influence intellectual abilities in OS patients, other brain defects of OS patients have not or only very vaguely been seen in the knock-out animals. Furthermore, overexpression of Mid1 protein carrying human OS mutations in KO animals does not rescue the phenotype but causes additional defects such as radial migration defects in the developing mouse cortex. This makes it likely that the function of wildtype and mutant MID1 differs between mouse and man and makes it important to study MID1 effects in human systems. In this project we will put together the experience of a human genetics group that has studied genetics and biochemistry of OS for many years and a stem cell group, which has focus¬¬ed on neural stem cells and neuronal connectivity. We will use iPS cells that we have generated from fibroblasts of 5 OS patients and isogenic controls to study neurodevelopmental defects in OS. We will differentiate the cells into neuronal precursors and into 2D neuronal cultures and 3D organoids and will study these morphologically, biochemically and functionally. Furthermore we will employ rabies virus-based tracing of neuronal connectivity in neuronal cultures and will use the same technique also in mouse cortex after transplantation of iPS-derived neurons in order to study neuronal function and connectivity. With this work we will be able to closely look at effects of mTOR/PP2A dysfunction on neuronal morphology, function and connectivity in humans. These studies will help us understand how mTOR/PP2A signalling influences some fundamental brain functions such as learning and memory and causes intellectual disability in patients.
DFG Programme
Research Grants
