Post-translational regulation of neuronal differentiation

Glycosphingolipids (GSLs) are amphipathic lipid moieties that make up only 3% of the total lipid content of the cell and are almost exclusively expressed at the Plasma Membrane(PM). They are key drivers of signalling hotspots known as ‘lipid-rafts’ as well as acting as primary signalling molecules themselves. Pathologically, perturbations in their synthesis (Knock-Out mice models) and disorders in their metabolism(Lysosomal storage disorders), both converge on neurological symptoms. In fact, during neuronal development, stem cells have been known to completely remodel their glycosphingolipid profiles, so much so, that the developmental stages of the nervous system have been associated with the expression of different glycosphingolipids. This coordinated change in the expression of glycosphingolipids has been previously attributed to the transcriptional shift in the the expression of genes encoding specific Glycosphingolipid Synthesizing Enzymes (GSEs) observed over neuronal development and, more recently, shown to be internally regulated by the GSLs themselves whereby globosides negatively regulate the expression of the ganglioside synthesizing enzyme GM3S via a neuronal transcription factor AUTS2. In this thesis I show that there exists an extra layer of post-translational regulation that is active over neuronal development that destabilizes the Gb3 synthesizing enzyme, Gb3S, on one hand while stabilizing the GM3S on the other. The regulatory mechanism achieves this effect by doubling the rate of degradation of Gb3S in neuronal cells, probably via membrane trafficking events. The exact details of the stabilization effect of GM3S remains to be determined as the results could not ascertain if it was the same mechanism or a completely different one. My study goes on to show that this regulatory mechanism is activated early during development, preceding the changes in canonical stem and neuronal markers. Morphologically, the study points towards a post-compaction but pre-cavitation (E2.5-E3.5) point of activation for the mechanism of Gb3S destabalization, relative to early mouse embryological development. Furthermore, I found that the Gb3S interactor and AUTS2 transcriptional target UCHL1 is a key regulatory unit of the machinery such that inhibiting its activity results in a specific rescue of the Gb3S enzyme.