Quantitative analysis of modulations in intramembrane particles during maturation of starfish oocytes

Abstract

The cell membrane of oocytes of the starfish Asterina pectinifera was investigated during maturation by freeze-fracture electron microscopy. On the micrographs of freeze-fractured oolemmas at various stages of maturation induced by 1-methyladenine, the intramembrane particles (IMPs) were counted and the size of each IMP was measured using an image analyzer. A 5-min treatment with the hormone lead to a decrease in IMP density on the E face and an increase on the P face. The most remarkable change in the density, an increase of 87% on the E face and a decrease of 42% on the P face, occurred within the following 5 min, the late “hormone-dependent period.” The mean value of IMP size first decreased on both faces, then gradually increased until values similar to those of the immature oocyte were reached. The results revealed that the hormonal signal to the surface receptors induces reorganization of the membrane components at the time of its action on the ooplasm, and that the oolemma also changes as a result of maturation of the ooplasm.