Membrane lipids composition and metabolism during early embryonic development phospholipid subcellular distribution and 32P labelling

Abstract Phospholipid composition and 32 P metabolism were studied in oocytes and early developing embryos of the toad, Bufo arenarum , Hensel. The content and distribution of phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidic acid, sphingomyelin, phosphatidylserine, and diphosphatidylglycerol in embryos, whole oocytes, and the subcellular fractions of both were determined. Phosphatidylcholine and phosphatidylethanolamine were the major constituents of yolk platelet. Diphosphatidylglycerol was confined to the mitochondrial fraction, where it represented 7% of the phosphoacylglycerols. Relatively large amounts of sphingomyelin were found in microsomal and postmicrosomal supernatants. After in vivo labeling with 32 P, the early development of individual phospholipids in subcellular fractions and in whole eggs was followed. The greatest uptake was found in mitochondrial and yolk platelet fractions. A steady increase in the amount of 32 P present in phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol was seen in the whole embryo from oocyte to late gatrula stage and in all subcellular fractions. Phosphatidic acid exhibited a slight decrease in specific activity, except in the yolk fraction. This high 32 P incorporation would indicate a rapid and uneven polar headgroup turnover determined by phospholipid class and subcellular fraction. At the same time, the phospholipid content of the subcellular fractions studied remained unchanged during early embryogenesis. Moreover, 32 P was actively incorporated into the individual phospholipids in the absence of measurable net synthesis.