Lipid droplet formation during vitellogenesis in the cecropia moth

Abstract

Lipid droplets isolated by flotation from the ovary of Hyalophora cecropia were shown to constitute about 12 per cent of the dry weight of the egg, and about 60 per cent of extractable egg lipids. A second form of lipid reserve, conjugated lipoproteins in the protein yolk spheres, presumably makes up much of the remaining 40 per cent. The lipid droplets were 82 to 85% triglyceride and 3 to 8% phospholipid. Total egg lipids by contrast were 63 to 70% triglyceride and 24 to 31% phospholipid. When 3H-palmitate was injected into the haemocoel, lipid droplets from vitellogenic follicles were found to be heavily labelled. After 24 hr, over 70 per cent of the total follicular radioactivity was found in the isolated lipid droplets, 90 per cent of that being in the form of triglycerides. Autoradiograms confirmed that the deposition of lipid droplets like that of the protein yolk spheres occurs in the peripherial cytoplasm of the oöcyte, adjacent to the follicular epithelium.