Role of Eed in neural stem cell lineage progression

Higher-order brain functions such as sensory perception, cognition, generation of motor commands, spatial reasoning and language are performed in the cortex. The cortex consists of a variety of different neuronal, glial and stem cell types that are generated from radial glial progenitors (RGPs) during embryonic developmental. Which mechanisms regulate the behavior of RGPs to ensure a correct generation of the cortex? Epigenetics, which define changes in chromatin structure without altering the DNA sequence, are thought to play a critical role in this process. This project will focus on a specific epigenetic modification, the attachment of which requires the protein embryonic ectoderm development (EED). EED is an interesting protein to investigate, since the impact of EED on cortical development remains mainly unresolved. In order to investigate the function of EED during corticogenesis, I will make use of a unique genetic model system termed Mosaic Analysis with Double Markers (MADM). MADM allows for generation of individual genetically altered cells surrounded by a healthy environment. Genetically altered cells will be color- labelled in green, whereas unperturbed cells will be labelled in red. Thereby, we can easily identify and investigate such cells in a quantitative and qualitative manner. We can identify, whether deletion of EED in individual RGPs alters the number of stem cells, neurons or glial cells produced during embryonic development The MADM technology is the only model system that enables us to investigate, whether it makes a difference if an EED mutant cell is surrounded by healthy cells or by a EED mutant environment. By performing next-generation sequencing on MADM-labeled cells, we will be able to identify critical molecular factors controlled by EED in RGPs. The results obtained from this study will provide a deeper knowledge on the function of factors controlling cortical development. Only when we understand developmental processes in more detail, we will be able to optimize disease diagnose and treatment. Thereby, my work will provide benefit for better characterization and therapy of neurological disorders such as autism, psychiatric diseases or brain cancer.

NICOLE AMBERG - PROJECT T 1031: HERTHA FIRNBERG FELLOWSHIP "THE ROLE OF EED IN NEURAL STEM CELL LINEAGE PROGRESSION" In her project, Dr. Amberg investigated the question of how a brain of correct size and cell composition is formed. During embryonic development, the stem cells of the cerebral cortex execute a series of genetic programs to produce a wide variety of cell types according to a fixed temporal pattern. First, different nerve cells are generated, followed by various glial cell types. It is a big open question which molecular and cellular mechanisms are needed to control the complex developmental pattern. Epigenetics are considered an important mechanism to regulate this process. Epigenetic mechanisms induce changes in DNA structure without changing the DNA sequence. This project focuses on a specific epigenetic modification, the delivery of which is assisted by the protein 'embryonic ectoderm development' which is encoded by the gene Eed. During this project, Dr. Amberg has already successfully shown in an international collaboration that Eed is of crucial importance for the timely activation of the distinct developmental programs. In a further step, Dr. Amberg studied the role of Eed at the single-cell level to find out exactly how Eed fulfills its function in individual cortical stem cells. Her results showed that within a normal cellular environment, a single Eed-mutant cell exhibits no impairment in the production of neurons in the cerebral cortex. This observation is in stark contrast to the finding that an Eed mutation in all stem cells of the cerebral cortex leads to a greatly reduced production of nerve cells and thus to a too small brain. Thus, the results illustrate that the genetic makeup of the cellular environment exerts a strong influence on the epigenetic regulation of molecular developmental programs in individual stem cells. In a deeper examination of the later stages of the development of the cerebral cortex - the formation of glial cells - Dr. Amberg found that individual Eed mutant glial cells showed fewer cell divisions. The impaired proliferation thus resulted in fewer glial cells being generated. In summary, this research project has discovered that Eed is required in individual stem cells in a stepwise manner to control the formation of a correctly assembled cerebral cortex. In addition, Eed is required in the totality of all stem cells to ensure that there is no overall systemic interference with the biological developmental program of the cerebral cortex. These results underline the importance of the interaction of individual cells with their cellular environment and are therefore of great use for better characterization and therapy of neurological diseases or syndromes caused by mutations in individual brain stem cells, such as autism, psychiatric diseases or tumors.