Lipid droplets have recently emerged as an exciting, disease relevant topic of research. Droplet biology is intrinsically linked to fat metabolism, which is in turn linked to a multitude of human diseases despite the obvious medical importance of lipid droplets, much of their cellular biology is poorly understood. It has recently become clear that throughout the animal kingdom lipid droplets are transported within the cell. It appears that the cellular region a lipid droplet is positioned to affects its metabolic state allowing cells to transport droplets into a ‘degradative region’ when starved or a ‘growth region’ when fed. Testing this hypothesis and examining the overall importance of lipid droplet allocation in the developmental system of the Drosophila embryo is the goal of this proposal. It is the Drosophila embryo where our mechanistic understanding of how lipid droplets are transported is the most advanced. While the impetus of previous such research was to understand general properties of active transport, I will now employ this system to droplet biology. The decades of transport driven research done by our lab has yielded a vast repertoire of genetic tools which I plan to utilize to interrogate the role transport mediated lipid droplet allocation between embryonic cells. My preliminary data shows that disrupting proper transport of lipid droplets along microtubules diminishes turnover of triglycerides (stored in lipid droplets) and may cause a delay in embryonic development. Intriguingly, droplet consumption because of improper intracellular positioning fits nicely with data gathered from mammalian systems: mouse embryos extensively reposition their lipid droplets post fertilization and mammalian cultured cells use microtubules to reposition droplets depending on nutritional status. These strong similarities between mammals and flies not only suggests conservation of transport mediated positioning of lipid droplets across taxa, but also supports the notion that lipid droplet positioning itself may be a means regulating cellular lipid metabolism. I will test this at an organismal level. This proposal aims to address why loss of lipid droplet based active transport impedes their consumption and how that that failed consumption would then delay embryonic development. It seems likely that improperly allocating droplets would cause a state of relative starvation in droplet-deprived cells. Mammalian cell culture system have elucidated several markers of cellular lipid starvation which I will examine in these lipid droplet deprived embryos. Next, the delay in embryogenesis is likely caused by diminished droplet consumption at the embryonic level which would globally diminish the energy supply. To pin this down, I will use a panel of genetic mutants, which fail in lipid droplet allocation to varying degrees, to extrapolate the relationship between failed lipid droplet consumption and delayed embryogenesis. These studies would constitute strong support of the role of lipid-droplet-transport-mediated cellular allocation and its importance for development.

Fats/lipids are a great source of energy and structural materials, and cells store them in structures called lipid droplets. Recent findings in isolated mouse cells suggest that the intracellular position of lipid droplets critically affects fat consumption. This proposal tests whether lipid droplet positioning acts similarly in an intact organism and whether it affects embryonic development.