SEIPIN, an evolutionary conserved protein, plays pivotal roles during lipid droplet (LD) biogenesis and is associated with various human diseases with unclear mechanisms. Here, we analyzedC. elegansmutants deleted of the sole SEIPIN gene,
seip-1. Homozygousseip-1mutants displayed penetrant embryonic lethality, which is caused by the disruption of the lipid-rich permeability barrier, the innermost layer of theC. elegansembryonic eggshell. InC. elegansoocytes and embryos, SEIP-1 is associated with LDs and crucial for controlling LD size and lipid homeostasis. Theseip-1deletion mutants reduced the ratio of polyunsaturated fatty acids (PUFAs) in their embryonic fatty acid pool. Interestingly, dietary supplementation of selected n-6 PUFAs rescued the embryonic lethality and defective permeability barrier. Accordingly, we propose that SEIP-1 may maternally regulate LD biogenesis and lipid homeostasis to orchestrate the formation of the permeability barrier for eggshell synthesis during embryogenesis. A lipodystrophy allele ofseip-1resulted in embryonic lethality as well and could be rescued by PUFA supplementation. These experiments support a great potential for usingC. elegansto model seipin-associated human diseases.