A morphologic,cytochemical, and chromatographic analysis of lipid yolk formation in the oocytes of the dog

The oocytes of carnivorous mammals are distinguished by the presence of large amounts of a lipid, yolk like material. In the oocytes of the dog, lipid yolk formation marks one of the earliest indications of occyte maturation. In early primary oocytes, the yolk bodies are scattered within the ooplasm, while in later stages they are in discrete clusters. Lipid yolk material appears to be formed by at least two mechanisms. Throughout most of oogenesis the oocyte contains scattered dense granular bodies that become vacuolated by droplets of lipid material and may be transformed, by this process, into lipid yolk bodies. These granular bodies are highly reactive for acid phosphatase and are positive for glycoprotein with the PA-CA-methenamine technique. In addition, other glycoprotiein-rich yolk bodies appear to arise from many of the small dictyosomes. In secondary follicles these two mechanisms often appear to act conjointly with the dense vacuolated granules coalesing with the larger yolk bodies. Small yolk bodies are intensely reactive for glycoprotein, becoming less reactive as they enlarge and mature. The developing yolk bodies are often associated with the acid phosphatase-positive granules. The peripheral portions of the larger yolk bodies are faintly reactive for both acid phosphatase and glycoprotein. All reactivity is lost in mature yolk bodies. Thin layer chromatography of the total lipids extracted from isolated oocytes reveals a pattern that is consistent among dogs of the same and of different breeds. The most abundant lipid fraction from each dog oocyte extraction stains strongly for glycolipid.