Cell cycle and epigenetic changes during neural differentiation in vertebrate embryos and ES cells

Understanding the molecular mechanisms that underlie the generation of nerve cells in the vertebrate embryo provides insight into the key steps that must take place during the production of nerve cells from embryonic stem cells in culture.

We have shown recently that a switch between two key cell signals (Fibroblast growth factor and Retinoic acid, a derivative of Vitamin A) controls the onset of nerve cell production.

We plan to build on this discovery and on new data which indicate that changes in the time a cell takes to divide and in the accessibility of genes to regulatory signals may be important steps that are controlled by this signal switch. The regulation and consequences of these changes in cell cycle time and gene accessibility will be investigated in detail in chick and mouse embryos. We also plan to carry out a screen to identify further changes in gene expression regulated by this signal switch.

This work will contribute to our basic understanding of the molecular basis of neural differentiation. It will also inform protocols for directing stable neuron production in embryonic stem cells and therefore help to develop therapies for treatment of neural injury or disease.

Identification of the sequential molecular interactions which underlie neural differentiation is fundamental to our understanding of vertebrate embryonic development and provides insight into the key steps that must take place during neural differentiation of Embryonic Stem (ES) cells in vitro. Recently, we have identified a signalling switch which controls the onset of neuronal differentiation and patterning in new neural tissue as it is generated in the embryo by a tail-end stem zone. This involves mutual opposition of Fibroblast Growth Factor (FGF) signalling, which promotes an undifferentiated cell state, and Retinoid signalling, which drives differentiation. Here I plan to build on this discovery and on new data which identify dramatic changes in cell cycle parameters and in epigenetic modification which prefigure the establishment of regulated neuron production. These maturation events will be investigated in detail in the embryo and in ES cells. Specifically, I plan to: i) Identify regulatory relationships between key signalling pathways that maintain the undifferentiated cell state in the tail-end stem zone; ii) characterise changes in cell cycle parameters and regulation as cells leave the stem zone, experience retinoid signalling and commence neuron production; iii) Investigate epigenetic events associated with changes in cell cycle which may underpin onset of neuron production; iv) Search for similar regulatory relationships, cell cycle and epigenetic changes in mouse ES cells undergoing neural/neuronal differentiation; v) Use GeneChip and accompanying bioinformatics approaches to identify key changes in gene expression in stem zone cells exposed to retinoic acid; vi) Develop a transgenic mouse in which gene expression is driven specifically in the tail end, to open the way to genetic investigation of differentiation in the embryonic neural axis. The overall aim of this work is thus to establish key signalling networks and regulatory mechanisms which govern the differentiation status of cells in newly generated neural tissue in the embryo, which we will use to inform our investigations of these processes during in vitro differentiation of ES cells.