Molecular control of self-renewal and neurogenic characteristics of cortical progenitors

Lead Research Organisation: King's College London
Department Name: Developmental Neurobiology

Abstract

The cerebral cortex plays a key role in many higher order functions in humans and therefore malformation or damage to the cortex greatly affects our well-being. The cortex is a tissue with very few adult stem cells and therefore has limited capacity to generate new neurons. Decoding the mechanisms that control the self-renewing potential of the cortical progenitors would shed light on the causes of neurodevelopmental disorders, and may also help to develop strategies to repair the damaged and/or aged cortex. My aim in this proposal is to investigate fate-switching mechanisms that change self-renewing progenitors into those capable of generating neurons in the cerebral cortex.
Early cortical progenitors are self-renewing and expand the population of progenitors. Subsequently they differentiate into neural progenitors, which undergo a limited number of cell divisions generating neurons. In other words cortical progenitors undergo fundamental changes in their characteristics during early corticogenesis: from self-renewing progenitors to neurogenic progenitors with limited self-renewing capacity but that competently generate neurons. But how the self-renewing and neurogenic progenitor fates are determined and how the transition processes regulated remains an important but unsolved question. Previously I have found that Fgf10, one of the fibroblast growth modulates differentiation of self-renewing to neurogenic progenitors. Based in my initial finding, I aim to identify novel factors determining the fate of self-renewing, neurogenic progenitors and its transition.

Determining the underlying mechanisms that control the decision of the neural progenitors to renew or differentiate is very important for at least two reasons. Firstly, balancing self-renewing proliferation and differentiation of neural progenitors is a crucial developmental mechanism to ensure proper growth of the nervous systems. Impairment of progenitor self-renewal results in immature and reduced brain growth, whilst uncontrolled over-proliferation often causes oversized brains and/or cancers. Secondly, the use of stem/progenitor cells offers enormous potential to develop novel strategies to repair damaged nervous systems with little natural regenerative capacity.

I firmly believe that the study proposed here will provide new findings to explain fundamental characteristics of cortical progenitors: self-renewing or competent for neurogenesis. This study will provide insights into the genetic program of cortical progenitors that determines their self-renewal potential and neurogenic competency. As the adult cortex has little potential for neurogenesis due of the lack of neural progenitors, developing a regenerative medicine approach is crucial for repair of the cortex injured by various mechanical damages, ischemia, or neurodegenerative diseases. Identifying and characterizing key factors of cortical progenitor differentiation as proposed here will not only shed light on the fundamental mechanisms of neural progenitor differentiation, but may provide us with genetic tools or help to discover drugs that enable direct reprogramming of in vivo differentiated cells (which can no longer regenerate neurons) into neurogenic or self-renewing progenitors. In a following project, I will test the possibility of whether my candidate genes could be utilized to reprogram differentiated cells into self renewal and/or neurogenic states that may provide newly generating neurons in the adult cortex.

Technical Summary

Cortical development starts with the self-renewing expansion of cortical progenitors called neuroepithelium cells (NE). Subsequently they differentiate into neural progenitors called radial glia (RG), which undergo a limited number of cell divisions generating neurons. In other words cortical progenitors undergo fundamental changes in their characteristics during early corticogenesis: from self-renewing progenitors that expand by symmetric (S) divisions to neurogenic progenitors with limited self-renewing capacity that competently generate neurons by asymmetric (AS) divisions.
Previously I have found that Fgf10, one of the fibroblast growth factors expressed at the NE-RG transition, modulates differentiation from NE to RG. This finding suggests that investigating Fgf10 signaling in cortical progenitors will allow us to identify the downstream targets controlling fate decisions of cortical progenitors regarding self-renewing or neurogenic. Also, given that Fgf10 is temporally expressed at the transition period of NE-RG differentiation, analyzing temporal expression over the time of NE-RG differentiation may identify other key fate determinants for NE or RG fates and those driving the differentiation from NE to RG.
Using a bioinformatics approach to analyze Fgf10-dependent gene expression profiles, as well as temporal gene expression at NE-RG transition, I have identified 29 candidates as regulators of NE-RG fate determinants. I will perform gain-of and loss-of function analysis of my candidates in ES-cell derived cortical progenitors to examine their activity on NE-RG differentiation. Next I will investigate whether candidates are capable of accompanied alteration of self-renewal and neurogenic potential within cortical progenitors in an in vivo mouse cortex. The outcome of this analysis would prove the in vivo roles of newly identified candidates on the self-renewing and neurogenic fate decision of cortical progenitors.

Planned Impact

Commercial and Economic Impact (year 3)
Although it is not envisioned that the proposed research will directly lead to results linked to the translational approaches, it is possible that we will uncover pathways that are disrupted in the neurodevelopmental diseases described above. In addition, identification of molecular machinery controlling self-renewing and neurogenic potential of progenitors could result in the development of regenerative therapies for neurodegenerative disorders. I am in discussion with several PIs at the Institute of Psychiatry (Drs Patrick Bolton and Sarah Curran) to seek strategies that link these genes regulating cortical progenitor differentiation to clinical aspects, and to search for mutations in my candidate genes in patients who show brain developmental disorders. Furthermore, insights into the key regulators of self-renewal and neurogenesis will pave the way for new drug discovery to stimulate/reactivate the self-renewal potential of stem cells. All discoveries from this proposal will be discussed with Kings Business and Innovation, an in-house service that advises King's College academics on pathways for the commercial and academic impacts. Services provided include the identification, protection and licensing of IP, support and advice on creating companies or identifying commercial partnerships with industry and identifying partners for the development and sale of reagents.

Advanced Training (year 1 -3)
Staff employed for the research project will receive training in a variety of research techniques, in particular ES cell manipulation, mouse genetics, mouse surgical methods, basic programming skills to process a large volumes of datasets (mainly by R and Ruby programming) as well as knowledge of neuroscience, design of projects and presentation/communication of science.
The importance and usefulness of ES/iPS cell technologies has been emphasized not only for academic research but also industrial aspects given the potential of stem cells for drug testing and as advanced biomaterials for transplantation. As such the postdoctoral researcher involved in this project would receive ideal training that will help him/her to progress his/her advanced career path either in academia or industry as well as being a bridge between these two fields. The postdoctoral researcher will also be involved in the supervision of lab projects that are part of the final year undergraduate BSc programs here at King's. In this way, we will provide an environment that will contribute to the training of scientists, and which will facilitate the development of other postdoctoral skills; enhancing their ability to manage, to teach, and to direct and supervise lab projects. This commitment will require postdocs to develop expertise in skills that will prove essential in their future career as scientist, but also in other professions.

Societal Impact (year 1-3)
The results of this work are likely to benefit researchers in a number of scientific fields and I have clear pathways to ensure this work will effectively impact all identified beneficiaries. The immediate field of developmental neuroscience will benefit from further insights into the spatial and temporal control of mechanisms that regulate cortical progenitors and stem cells, which will also have impacts on clinical research related to brain size disorders such as autism. I believe strongly that my proposed research will help to provide new avenues for the development of diagnosis and treatment of brain disorders and injury. Our work will therefore have impact on UK society and we will ensure that members of the public have access and gain understanding from our work by engaging in activities that communicate or share our work with the public.

Publications

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