Distributional changes of 32P-labeled acid-soluble phosphates and phospholipids among subcellular fractions during early vertebrate embryonic development

Abstract

Early developing embryos of the toad Bufo arenarum Hensel were employed to study the content and in vivo labeling with 32P of the acid-soluble phosphates and phospholipids at the subcellular level. The radionuclide was administered to the female toad along with the pituitary extract used to induce the ovulation. Most of the total phospholipids (68%) and proteins (84%) are confined to the yolk platelet fractions. Up to the heart beat stage (130 h of development) there are no significant changes detectable in protein and phospholipid content. The total P content in trichloroacetic acid-soluble fraction was distributed mainly between postmitochondrial supernatant (58%) and yolk platelet fraction (37%) in the unfertilized oocyte. As development proceeds an increase was observed in the former and a decrease in the latter. The acid-solube phosphates in the mitochondrial fraction only amount to 4% of the total embryo throughout the examined stages. The unfertilized oocyte contains about 98% of acid-soluble phosphates labeled with 32P in the postmitochondrial supernatant and as development proceeds a striking decrease was found to occur while the radioactivity in the acid-soluble phosphates of mitochondrial and yolk platelet fractions increases significantly during the studied stages. About 11.5% of the lost radioactivity from the acid-soluble phosphates was found to be used to label the phospholipids.