Transcriptional mechanisms of neural stem cell maintenance and neurogenesis

The purpose of this project is to better understand how stem cells decide whether to multiply or to generate nerve cells. Stem cells are the crucial progenitor cells that generate all the specialized cells that form the organs in the embryo. They are also present in adult organs where they are required for maintenance and repair. Each organ has its own stem cells that generate the particular cell types of that organ. In medicine, stem cells can be used to replace cells that are damaged in diseases; for example blood stem cells are used to treat leukemias. In order to extend their usage to the treatment of other diseases, we must learn much more about how stem cells work. In particular we need to better understand the process by which a stem cell becomes specialised to generate one kind of cell rather than another. In this project, we will study how stem cells of the nervous system (called neural stem cells) become specialized in the generation of nerve cells (neurons). This process involves a profound change in the set of genes that are active: genes that present in stem cells are shut down, while genes characteristic of neurons become active. Gene activity is controlled by proteins called transcription factors. One of the main transcription factors that controls the generation of the neurons of our brains is called Ascl1. The primary purpose of this project is to understand how Ascl1 changes the set of active genes in neural stem cells so that these cells generate new neurons.

Transcription factors work by binding to DNA near the genes they activate. They bring with them a multitude of other factors (called cofactors). Some of these cofactors modify the proteins that coat the DNA, others increase the contact of transcription factors with the DNA, and together they are directly involved in activating or inactivating genes. In this project, we will identify the cofactors that help the transcription factor Ascl1 activate the genes required to generate neurons. We will also identify the cofactors that prevent the inappropriate activation of genes that promote the generation of other kinds of cells.

Our adult brains contain very few stem cells, which means they are limited in their ability to recover from brain damage and disease. Understanding the machinery that makes neural stem cells produce neurons can help us develop ways to replace lost brain cells. This can be done either by activating the resident stem cells, or transforming non-brain cells (e.g. skin cells) into neurons. In either case, these can then be transplanted or used to test drugs for their ability to treat neurological diseases, and hence have the potential to offer therapeutic solutions to a variety of currently untreatable conditions. This project will help in this endeavour by identifying ways to help stem cells of the brain generate more neurons.

Our main objective for this proposal is to elucidate the molecular mechanisms underpinning the dual function of the cell fate determinant Ascl1 in proliferation and in neuronal differentiation of neural stem cells (NSCs). We have previously shown that Ascl1, a transcription factor with a central role in neurogenesis and in neuronal reprogramming, has distinct roles and regulates different target genes in NSCs and in differentiating neurons. We also found that Ascl1 associates with both transcriptional activators and transcriptional repressors in the same cells. In this project, we will test the hypothesis that Ascl1 maintains NSCs by recruiting transcriptional activators to genes such as cell cycle regulators that are expressed in NSCs, and by simultaneously recruiting transcriptional repressors to neuronal and glial genes to prevent their premature expression in NSCs. We will also test the prediction that Ascl1 promotes neurogenesis by recruiting transcriptional activators to neuronal-specific genes while in parallel recruiting transcriptional repressors to genes involved in NSC or astrocytic-specific programmes that must be suppressed in neurons.

This project will shed new light on how neural cells coordinate a cell type-specific gene expression programme with the suppression of alternative programmes. It will also give insights into the mechanisms that allow the same transcription factor to exert different fonctions at distinct stages in the same lineage. Beyond these immediate impacts, this project will contribute to the current efforts to improve the efficiencies of direct reprogramming of fibroblasts and of differentiation of puripotent cells into neurons. Finally, by elucidating the fundamental mechanisms of NSC maintenance and differentiation, we will eventually be in the position to ask how these mechanisms are affected by physiological changes such as ageing, in which the output of adult NSCs is derailed.

The prime beneficiaries of the project will be stem cell scientists, in particular researchers in the field of reprogramming of cell fates, and researchers studying tissue stem cells such as blood, muscle or skin stem cells. We will have proactive strategies to reach these scientists and ensure that the ideas and candidate molecules arising from our research are tested in protocols for direct neuronal conversion of differentiated cells and for neuronal differentiation of ES and iPS cells and for studies of lineage restriction of tissue stem cells. One approach will be to contact prominent scientists working on neuronal reprogramming and on tissue stem cells, many of whom we know and some of whom we already collaborate with. We will identify other scientists in these fields through litterature searches and attendance of stem cell conferences and we will invite them to NIMR to expose them to our research and propose collaborations. We will also offer to host trainees in their labs for periods of weeks to several months, as we have done multiple times in the past, for training in the techniques we use and to promote deeper interactions and maximize the chance of successful collaborations.

If we find during the course of the project that our results could potentially be used to improve existing methods of neuronal reprogramming or neuronal differentiation of iPS cells (this will be assessed by lab members not involved in the project who study neuronal reprogramming), we will immediately take action by consultating with the Technology Transfer Officer at NIMR and the Business Manager at MRC Technology to consider the need to protect our findings for possible future commercial exploitation. We will also canvas biotech companies and scientists advising such companies for their interest in collaborating with us to develop better assays to test drugs on patients-derived neurons.

To reach a larger audience beyond the circle of stem cell scientists we already interact with, the publication of our results will be essential. We will pursue our policy of publishing our research in journals with broad readership. This will be complemented by a more proactive strategy to extend our reach to audiences in other fields of research or those that may not read primary research papers, by offering to write "primer" or 'community page" type articles in academic journals. To reach further audiences through the internet, detailed information on the project will be included in the webpage of the Guillemot laboratory on the NIMR website and in other appropriate websites such as 'the Node' recently setup by the Journal Development, with specific calls for collaboration.

It is also an important responsibility of scientists to engage with the wider public, particularly on issues such as stem cells that have a huge medical potential and generate much interest. Our main strategy will be to invite secondary school students in North London schools every year for the duration of the project, to spend the summer in the lab shadowing lab members, as we have done in the past. A named postdoctoral researcher in this project, Ben Martynoga, has a particular interest in communication of science to the public and has applied for a Media Fellowship from the British Science Association. Should he succeed, the experience he will acquire during the several week placement offered by BSA will be invaluable to develop effective approaches to communicate our research to a general audience.