A flexible network of lipid droplet associated proteins support embryonic integrity of C. elegans

In addition to coordinating the storage and mobilization of neutral fat, lipid droplets (LDs) are conserved organelles that can accommodate additional cargos in order to support animal development. However, it is unclear if each type of cargo is matched with a specific subset of LDs. Is the identity of each subset rigidly maintained? Here, we report that SEIP-1/seipin defines a subset of oocyte LDs that are required for proper eggshell formation in C. elegans . Using a photoconvertible fluorescent protein-based imaging assay, we found that SEIP-1 positive LDs were selectively depleted after fertilization, coincident of the formation of a lipid-rich permeability barrier of the eggshell. Loss of SEIP-1 function caused impenetrant embryonic arrest, which could be suppressed by depleting a LD-structural protein PLIN-1/perilipin. The embryonic development of seip-1; plin-1 mutant in turn depended on another LD-associated protein, RAB-18/Rab18. Our results are consistent with the hypothesis that SEIP-1 dependent and independent mechanisms act redundantly to ensure the packaging and export of lipid-rich permeability barrier constituents via LDs. The identity of these LDs, as defined by their associated proteins, exhibits unexpected plasticity that ultimately ensures the survival of embryos ex utero.