Cortical Granules of Mammalian Eggs

Abstract

Publisher Summary Cortical granules are small, spherical, membrane-limited organelles found mostly beneath the oolemma of the unfertilized ovum. During folliculogenesis, the onset of cortical granule formation parallels the hypertrophy and hyperplasia of the Golgi complexes. As transformation of Golgi complexes occurs, they migrate centrifugally into the subcortical region of the oocyte. The Golgi complexes, in concert with the granular endoplasmic reticulum, are implicated in cortical granule formation. In this process, the contents of the cortical granules are packaged into membrane-limited granules. In most species, the formation of cortical granules ceases at ovulation, however, continued accumulation of cortical granules occurs in oocytes of a few species. The size of the cortical granules and the density of their matrix show considerable species variation. In the unpenetrated tubal eggs, cortical granules form an irregularly spaced monolayer beneath the plasma membrane. A polarity in the distribution of cortical granules is well exhibited in oocytes of some mammals; cortical granules are absent in much of the egg hemisphere homolateral to the meiotic spindle. Cortical granule exudate contains a trypsin-like protease; histochemical observations show both protein and polysaccharide components in cortical granules. At fertilization, the spermatozoon induces the cortical reaction.