Polycomb repressive complex 2 regulation of neurogenesis

A large number of processes that do not directly change genes, "epigenetic mechanisms" affect embryonic development and disease. One set of epigenetic proteins (PRC2) are central players in development. PRC2 controls stem cell development into many different cells and tissues of the body. Scientists do not know how PRC2 regulates embryonic or adult stem cells to make neurons. In this project, we propose to combine the Shen laboratory expertise in PRC2 biology with the Szele laboratory expertise in adult brain stem cells. We will investigate how PRC2 normally works and how it works after brain injury. We believe our collaborative work will discover epigenetic regulation of stem cells in nerve cell generation, and provide novel insights into stem cell therapy.

The postnatal and adult SEZ contains stem cells and exhibits robust neurogenesis. Several diffusible molecules and transcription factors regulate SEZ neurogenesis. Whilst a few epigenetic mechanisms have been implicated in SEZ cell generation the role of polycomb repressive complex 2 (PRC2) is unclear. The canonical PRC2 complex consists of EED, Suz12, and Ezh2, with Jarid2 frequently contributing to it as well. PRC2 functions to methylate lysine 27 of histone 3 (H3K27me3) via interactions with the methyl transferase enhancer-of-zest 2 (Ezh2). Whereas PRC2 and Ezh2 serve to balance self-renewal versus differentiation and neuron versus glial fate choices in early and late embryogenesis respectively, their roles in the neonatal and adult SEZ are unknown. In this project, Ezh2 function will be removed in the neonatal SEZ via cre-lox approaches to determine its role in neurogenesis. We will also knockdown Jarid2 and Eed and have shown in pilot work that this increases the number of self-renewing neurospheres, suggesting PRC2 maintains neural stem cells in quiescence.

A major component of our work will involve making biotin- and FLAG-tagged knockin mice which will express tagged Jarid2 and EZH proteins underlying their own endogenous promoters. These knockin mouse models will allow us to study epigenetic regulation of neural development.

Whereas the postnatal and adult SEZ mounts a response to injury in an attempt to repair, it only does so inefficiently. Since epigenetic mechanisms persist for protracted periods and seem to lock cells into a state of either pluripotency or differentiation we hypothesise they may act as "master regulators" that limit neural repair. We will test this hypothesis by modulating Jarid2, Eed and Ezh2 in the context of neonatal traumatic brain injury.

This interactive grant will both generate data and provide mutually beneficial interactions between the Szele laboratory (University of Oxford, Oxford, UK) and the Shen laboratory (Tsinghua University, Beijing, China). Prof. Shen is an internationally recognized expert in epigenetic mechanisms regulating embryonic stem cells. Thus the immediate Oxford University stem cells community (Oxford Stem Cell Institute) will benefit. Dr. Shen will have the opportunity to give a lecture during her Oxford visit and will interact with other faculty. We plan to develop a longer collaboration and if that is successful, the wider UK stem cell community will benefit as well.

Our collaborative work will enhance communication and interactions between the UK and Chinese stem cell communities. This is a very exciting prospect as the UK has long-standing strengths in stem cell biology and China has rapidly burgeoning capital and intellectual resources.

One of the major goals of our work is to discover molecular interactors of PRC2. It is likely that many of the molecules we find will be suitable for pharmacological targeting and if this is the case, many industrial, academic and patient beneficiaries will emerge.

Our work will immediately benefit developmental biologists, neuroscientists and clinicians interested in adult neurogenesis. Very little is known about how epigenetic mechanisms affect adult neurogenesis. Our work will also help elucidate if manipulating epigenetic mechanisms ameliorate the endogenus repair potential of adult neurogenic stem cells.

Finally construction of Biotin and Flag-tagged knockin mice will provide an invaluable resource for the epigenetic community and allow investigation of PRC2 function not only in neurogenesis but in all cell types.