An ultrastructural study of oocyte atresia in the starfish Pisaster ochraceus

The alterations involved in oocyte atresia of the starfish Pisaster ochraceus were investigated using both light and electron microscopy. It was shown that atresia may be defined by three patterns of cell destruction. Initially, the small electron-lucent vesicles produced by the Golgi complex underwent amalgamation into groups. This was followed by loss of vesicle membranes and consequent formation of transparent necrotic zones in the cytoplasm. The second pattern, ultrastructurally comparable with autophagic cell death, was marked by apparent amalgamation of the morphologically similar electron-lucent vesicles into growing vacuoles, giving rise to a multibranched autophagic vacuole. This vacuole engulfed the cytosol granules and ultimately came to occupy the entire space within the oocyte. In addition, the cytosol insulation inside of the ‘apoptotic body-like spheres’ was regularly observed. Thus, it is supposed that oocyte destruction may occur by a complex mechanism that includes elements of necrosis, autophagic cell death and apoptosis.