Degradation of yolk platelets in the early amphibian embryo is regulated by fusion with late endosomes

The eggs of many animal species contain a large store of yolk platelets, li pid droplets and glycogen granules; these are consumed during early embryog enesis. However, the mechanisms by which degradation of these stored materi als occurs during early embryogenesis are not clearly understood. The mecha nisms underlying yolk degradation in amphibian (newt) embryos were investig ated. Electron microscopy using an anion marker, cationic ferritin, reveale d that yolk platelets were degraded after fusion with late endosomes contai ning primary lysosomes. Electron microscopy and the results of experiments using a number of reagents with selective effects on intracellular transpor t suggested that yolk degradation activity in early amphibian embryos may b e regulated at the point of fusion between late endosomes and yolk platelet s.