Prolonged osmification as an indicator of the differentiation process in the endomembrane system

The technique of prolonged osmification was used in the analysis of reducing capacity of perinuclear space, endoplasmic reticulum and cis-Golgi cisternae in different epithelial cells during embryonic differentiation and immediately after the birth. Cells of the mouse gastric and intestinal epithelium and of the exocrine pancreas and mammary gland were analyzed. It was shown that endomembrane compartments exhibit high variability in their capacity to reduce OsO4 into lower valency oxides. Typical staining of cis-Golgi cisternae by osmium black does not occur before the cells achieve the developmental state in which production of specific products starts. The changes in stainability occurring from the perinuclear space and endoplasmic reticulum towards the cis-Golgi cisternae indicate a maturation pathway with no direct correlation to the chemical characteristic of the substances produced in different cell types. In the mammary gland the reduction capacity of endoplasmic reticulum disappeared with the intensive synthesis of lipids. Considering our previous results and those of other authors, the possible reasons for the observed dynamics in reducibility in particular segments of endomembraneous space are discussed.