Origin and cytochemisty of the animal dimple granules in Discoglossus pictus (Anura) eggs.

At the centre of the animal hemisphere of the 1000 micron ovarian oocytes of Discoglossus pictus there is the germinative area, a slightly depressed disc, 700 micron wide. During the passage of the oocyte through the oviduct this area becomes invaginated to form the 'animal dimple', which is the only site where successful sperm entrance can occur. Granules (G) with a central electron-dense core and a peripheral portion containing sparse fibrous material are found in the peripheral cytoplasm of the animal dimple. The origin and the cytochemistry of G's have been investigated. G's originate from Golgi complexes located in the peripheral cytoplasm of the germinative area only. Recently formed G's migrate to the oocyte cortical region, where vesicles appear to participate in G's maturation. The core of G's can be digested by pronase, is negative to a test for acid phosphatase detection, and contains a few polysaccharide complexes. In view of their origin from Golgi complex, their location in the oocytes and their exocytosis upon activation, G's seem to correspond to the typical cortical granules of Anurans. However, they appear to have a macromolecular content different from that of the cortical granules.