Molecular and cell biological mechanisms mediating re-establishment and maintenance of cell polarity in the developing CNS

Newborn neurons in the spinal cord of the developing embryo shed their tips to move to their final location. As a result of this shedding event, these newborn neurons lose key proteins that allow them to distinguish their front from their back, causing them to lose polarity. Following this, the neuron must now rapidly repolarise itself. This repolarisation is crucial, as it allows the neuron to extend a long cell-process, called an axon, which makes connections with its targets, which could be muscles or other neurons. In the developing embryo, the neuron repolarises in response to external signals from the surrounding tissue. These external cues determine the position of this repolarisation and therefore determine the direction in which the axon will travel, or if it forms at all. This is thus a critical event that is essential for the formation of functional neuronal circuitry. I propose to study the molecular and cellular mechanisms that direct this key cell-biological process, and a better understanding of this will ultimately lead to the possibility of manipulating and/or stimulating it to treat neural disorders during embryogenesis and adulthood. Additionally, many cancer cells also undergo a very similar repolarisation process during the process of metastasis, which allows them to migrate to different locations and form more tumours. It is likely that the cancer cells do this in a way similar to newborn neurons, so understanding neuron repolarisation will potentially also help us to understand how cancer cells migrate to form secondary tumours. Thus understanding how cells repolarise in response to surrounding tissues has far-reaching consequences.

Cells differentiating into neurons in the developing spinal cord undergo an acute loss of apical polarity during delamination from the neuroepithelium through the regulated process of apical abscission. The nascent neuron must now rapidly re-establish polarity to determine the position of axon outgrowth. Correct positioning of the nascent axon is crucial, as it will ultimately lead to the formation of functional neural circuits. However, the molecular mechanisms that re-specify the first neuron asymmetry following the acute loss of polarity mediated by apical abscission, and how this asymmetry is sustained remain unclear. These important biological questions will be studied using cutting-edge methods to image spinal cord neurogenesis in real time at high spatial and temporal resolution in ex-vivo tissue slices, allowing observation of dynamic cell-biological processes in individual cells within the developing spinal cord. This assay will therefore allow observation and manipulation of neuron repolarisation within the developing tissue, and and has already started to uncover novel and exciting cell biological behaviours that only take place within a tissue context.
Specifically, in this project I will: i) Determine the role of the centrosome during neuron repolarisation and axon extension. ii) Determine the role of the primary cilium during neuron repolarisation and axon extension. iii) Determine the molecular events specifying early neuron asymmetry. Overall, this proposal will advance our understanding of the molecular and cell-biological events involved in the reestablishment and maintenance of polarity in newborn neurons in response to extracellular cues from surrounding tissues.
Additionally, these studies will ultimately also be valuable for future studies in other contexts where cells undergo repolarisation events, including mesenchymal to epithelial transitions (MET), wound healing and tumour cell metastasis.

The most direct pathway to impact for this project will be through publication in journals with high impact, covering a readership beyond the cell and developmental biology community. In the longer term, understanding the molecular mechanisms directing neuron repolarisation may ultimately lead to the possibility of treating or manipulating neural disorders during embryogenesis and adulthood. Additionally, these mechanisms are also likely to be shared with other normal developmental processes, including EMT, as well as in the context of tumour cell metastasis and. The outputs of this proposal are therefore likely to impact a wider range of disciplines beyond neural development.

This research project is likely to be impactful beyond the academic setting. Research into neural development draws a considerable amount of public interest due to its importance for human health and disease. The time-lapse imaging used in this proposal generates visually striking movies of cells undergoing neuronal differentiation in the developing spinal cord and brings a complicated developmental process to life for the general audience, particularly younger people. These are therefore an ideal medium for use in public engagement and will be particularly useful for inspiring the next generation of young scientists.

The dynamic and visual nature of the timelapses also serve as an ideal medium for demonstrating how complicated molecular cascades are integrated to orchestrate key cellular processes leading to the formation of normal tissue architecture during embryonic development. As a result, in addition to its potential role as a tool for public engagement, the data generated during this project will also serve as an invaluable tool for teaching, both in schools and in universities in the UK and abroad.