The role of microRNAs in the regulation of neural stem cell development

Stem cells generate all the cells in the human body. They divide in a way that produces one daughter cell that remains a self-renewing stem cell, and one daughter cell that differentiates into a more specialised cell. The regulation of stem cell number and division is crucial for the appropriate growth of tissues. Stem cells must strike a balance, producing a sufficient number of self-renewing daughters to generate tissues of appropriate size and complexity, but not so many that cancerous growth occurs. Understanding the mechanisms underlying the behaviour of stem cells and their progeny contributes to both our understanding of normal development and also allows us to identify novel targets for the treatment of disease.

In both the Drosophila brain and the human brain neural stem cells initially divide to expand the pool of stem cells, then convert to cells that divide to self-renew and produce differentiated neurons. The striking similarity between the development of the Drosophila and the human brains suggests that the mechanisms regulating neural stem cell division may be conserved between flies and mammals. Indeed, 75% of human disease genes are conserved in Drosophila.

The goal of the proposed research is to investigate the role of microRNAs (miRNAs) in regulating the division of Drosophila neural stem cells. miRNAs are short pieces of RNA that have the ability to negatively regulate the expression of their target genes. We aim to identify miRNAs that are expressed specifically in neural stem cells. We will perform experiments to investigate the specific function of each miRNA and to identify the targets genes upon which they act. Our goals if to identify miRNAs, their targets, and the pathways in which they act in the Drosophila brain that are conserved in the human brain. These pathways could be drug targets for medical intervention in the treatment of both neurodegeneration and brain neoplasms.

The Drosophila central nervous system (CNS) has proved a fertile ground for studying neural stem cells and, more recently, how unregulated division in a stem cell lineage can lead to tumourigenesis. In the optic lobe of the larval brain, neural stem cells initially divide symmetrically within a pseudostratified neuroepithelium, expanding the pool of proliferating precursor cells. As development progresses neuroepithelial cells are converted to asymmetrically dividing neuroblasts which produce the differentiated neurons that will make up the visual processing centre of the brain. The progression from symmetrically dividing neuroepithelial cells to differentiated neurons in the optic lobe mirrors that seen in vertebrate neural development. The striking similarity between the development of the optic lobe and the mammalian cerebral cortex suggests that the molecular mechanisms regulating the transition from symmetric to asymmetric stem cell division may be conserved between flies and mammals. The goal of the proposed research is to investigate the role of miRNAs in regulating the timing of the switch from neuroepithelial cells to neuroblasts in the optic lobe. We will profile the genome wide binding of PolII in neuroepithelial cells and neuroblasts using Targeted DamID. From these data we will identify miRNAs specifically expressed in neuroepithelial cells and neuroblasts. We will determine the role each identified miRNA plays in the neuroepithelial cell to neuroblast transition using misexpression, knock-down, and knock-out experiments. We will isolate cell type specific miRNA target genes by immunoprecipitation of GFP tagged AGO-1 expressed specifically in neuroepithelial cells and neuroblasts. Validation of the target genes will allow us to determine the pathways in which each miRNA acts. This identification of miRNAs, their targets, and the pathways within which they exert their effects will characterize novel mechanisms of neural stem cell development.

The expected beneficiaries of the research detailed in this proposal include the i) The medical and pharmaceutical industries; ii) Businesses recruiting graduate-level staff; v) The third sector; vi) Schools; and vii) The general public.

The medical and pharmaceutical industries:
75% of human disease genes are conserved in Drosophila. The proposed research will identify miRNAs, and their targets, that regulate the switch from proliferation to differentiation. In so doing, we will uncover conserved regulatory pathways that are crucial for the control of neural stem cell proliferation. These could be prime drug targets for medical intervention in the treatment of brain neoplasms and neurodegeneration. In the long-term (>10 years) our results could impact the medical and pharmaceutical industries, helping to improve health and quality of life.

Businesses recruiting graduate-level staff:
The research proposal involves training that will ultimately prepare our staff for highly skilled employment in the private and public sectors. Former members of the lab have progressed to successful careers in the biotechnology industry, in consulting and in publishing, as well as in the medical, charitable and public sectors. The skills obtained in our lab are likely to produce individuals who will have a have a major impact on both the economy and the well-being of society.

The third sector, schools, and the general public:
Our group is heavily involved in science communication and outreach activities, both in schools and to the general public. Past examples include public lectures, radio interviews, University open days, school careers fairs, and, as of this year, involvement in the newly opened educational charity, Cambridge Science Centre. We will continue to promote greater awareness of science within the community, encouraging primary and secondary school students to consider science as a career. In particular, we aim to encourage young girls and women to participate in STEM subjects. We will disseminate the results of our research to the widest possible audience.