Fusion of fertilized and unfertilized sea urchin eggs: Maintenance of cell surface integrity

Abstract

Here we report that immediately after the fusion of a fertilized and an unfertilized egg, the two halves of the fused egg retain their respective cell surface organizations. Long microvilli are present on that area of the surface contributed by the fertilized egg, and the unfertilized portion remains comparatively smooth. Cortical granules are absent in the cortex contributed by the fertilized egg, whereas these organelles are present in the cortex of the unfertilized portion. There are distinct boundaries formed by the presence or absence of long microvilli and of undischarged cortical granules. However, following the synchronous prophase of the two nuclei, the original fertilized and unfertilized portions are no longer distinguishable. The observations indicate that the unfertilized portion of the fused egg is capable of maintaining its original surface properties but can, during prophase, undergo changes equivalent to those that take place at fertilization.