Structural heterogeneity of yolk spheres in hierarchical follicles from hen ovary: a histochemical study

Abstract

1. Four types of yolk spheres with variable structure, chemical composition and frequency of occurrence in yolk plasma of hierarchical follicles (F4, F3, F2 and F1 with diameters of 10·0, 15·5, 20·0 and 35·0 mm, respectively) of the hen ovary were identified using histochemical methods for localising lipids, carbohydrates and proteins. 2. Yolk spheres of the first type (YS1) had a phospholipoprotein membrane surrounding fluid matrix which stained lightly for phospholipids, proteins and acidic mucopolysaccharides. Two types of droplets were observed in the matrix of YS1. Spheres of the second type (YS2) had a lipoprotein- and acidic mucopolysaccharide-rich peripheral region and a single large droplet in its fluid matrix. Droplets of YS2, unlike YS1, showed three regions and metachromatic staining with ninhydrin–Schiff reagent. The third type of sphere (YS3) had a homogeneous matrix staining for proteins, neutral lipids and florescent yellow with alcian blue and differentially with ninhydrin–Schiff reagent; it was bounded by a phospholipids- and acidic mucopolysaccharide-containing thick peripheral region. Its fluid matrix also showed toluidine-blue-positive, densely packed granules and small droplets. The fourth type (YS4) was seen only in bromophenol blue and Nile blue preparations, revealing the presence of proteins and neural lipids in their matrix and peripheral regions. 3. Quantitative data on the relative abundance of yolk spheres in F4 to F1 follicles revealed more YS3 (51·1 to 64·7%) than YS1 (16·2 to 28·3%) and YS2 (19·1 to 23·2%). The percentage of YS1 increased and that of YS3 decreased as follicle size increased.