(666g) The Interplay Among De Novo Formation, Fission, and Lipolysis in Lipid Droplet Organelle Distribution in Dividing Eukaryotes

One of the key questions in cell biology is how daughter cells inherit organelles from the parent cell. To help address this question, I simulated lipid droplets as model organelles in dividing fission yeast cells. Lipid droplets are dynamic bodies that store neutral lipids and can form both de novo (biogenesis) and by fission, they can also be broken down (lipolysis) for energy or phospholipid needs. The quantitative interplay between formation and breakdown mechanisms is unknown but would seem crucial for controlling neutral lipid distribution, especially in dividing cells. Because long-term microscopy experiments over times that would cover multiple division cycles would be challenging, I instead used Brownian Dynamics simulations to quantify droplet distribution in populations of dividing cells. Simulation parameters were obtained from time-lapse confocal microscopy experiments of lipid droplets in live fission yeast cells. Of the three main events studied: biogenesis, fission, and lipolysis, the third plays the key role. Droplets must persist (not be completely broken down) for the number and volume of droplets to be stable in dividing cells even with very high de novo formation and fission rates. Thus, the sustained presence of droplets – most likely through connections with the endoplasmic reticulum – seems necessary for this organelle’s experimentally observed distribution in dividing eukaryotes.