Journal of Lipid Research, Vol 28, 100-107, Copyright © 1987 by Lipid Research, Inc.
Phospholipid transfer activities in toad oocytes and developing embryos
A Rusinol, RA Salomon and B Bloj
The role of lipid transfer proteins during plasma membrane biogenesis was
explored. Developing amphibia embryos were used because during their growth
an active plasma membrane biosynthesis occurs together with negligible
mitochondrial and endoplasmic reticulum proliferation. Sonicated vesicles,
containing 14C-labeled phospholipids and 3H-labeled triolein, as donor
particles and cross-linked erythrocyte ghosts as acceptor particles were
used to measure phospholipid transfer activities in unfertilized oocytes
and in developing embryos of the toad Bufo arenarum. Phosphatidylcholine
transfer activity in pH 5.1 supernatant of unfertilized oocytes was 8-fold
higher than the activity found in female toad liver supernatant, but
dropped steadily after fertilization. After 20 hr of development, at the
stage of late blastula, the phosphatidylcholine transfer activity had
dropped 4-fold. Unfertilized oocyte supernatant exhibited
phosphatidylinositol and phosphatidylethanolamine transfer activity also,
but at the late blastula stage the former had dropped 18-fold and the
latter was no longer detectable under our assay conditions. Our results
show that fertilization does not trigger a phospholipid transport process
catalyzed by lipid transfer proteins. Moreover, they imply that 75% of the
phosphatidylcholine transfer activity and more than 95% of the
phosphatidylinositol and phosphatidylethanolamine transfer activities
present in pH 5.1 supernatants of unfertilized oocytes may not be essential
for toad embryo development. Our findings do not rule out, however, that a
phosphatidylcholine-specific lipid transfer protein could be required for
embryo early growth.
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