Abstract

Post-fixation with osmium tetroxide staining and the embedding of Epon are robust and essential treatments that are used to preserve and visualize intracellular membranous structures during electron microscopic analyses. These treatments, however, can significantly diminish the fluorescent intensity of most fluorescent proteins in cells, which creates an obstacle for the in-resin correlative light-electron microscopy (CLEM) of Epon-embedded cells. In this study, we used a far-red fluorescent protein that retains fluorescence after osmium staining and Epon embedding to perform an in-resin CLEM of Epon-embedded samples. The fluorescence of this protein was detected in 100 nm thin sections of the cells in Epon-embedded samples after fixation with 2.5% glutaraldehyde and post-fixation with 1% osmium tetroxide. We performed in-resin CLEM of the mitochondria in Epon-embedded cells using a mitochondria-localized fluorescent protein. Using this protein, we achieved in-resin CLEM of the Golgi apparatus and the endoplasmic reticulum in thin sections of the cells in Epon-embedded samples. To our knowledge, this is the first reported use of a far-red fluorescent protein retains its fluorescence after osmium staining and Epon-embedding, and it represents the first achievement of in-resin CLEM of both the Golgi apparatus and the endoplasmic reticulum in Epon-embedded samples.

Highlights

  • Post-fixation with osmium tetroxide staining and the embedding of Epon are robust and essential treatments that are used to preserve and visualize intracellular membranous structures during electron microscopic analyses

  • We show that a far-red fluorescent protein, m­ Kate[210], retains fluorescence after osmium tetroxide staining and Epon embedding, and report the achievement of in-resin correlative light-electron microscopy (CLEM) of the Golgi apparatus and endoplasmic reticulum (ER) in Epon-embedded cells using this protein

  • We first investigated whether or not the fluorescence from mKate[2] was preserved following prefixation with glutaraldehyde and postfixation with osmium tetroxide, which are procedures that are necessary for processing electron microscopy samples

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Summary

Introduction

Post-fixation with osmium tetroxide staining and the embedding of Epon are robust and essential treatments that are used to preserve and visualize intracellular membranous structures during electron microscopic analyses. These treatments, can significantly diminish the fluorescent intensity of most fluorescent proteins in cells, which creates an obstacle for the in-resin correlative light-electron microscopy (CLEM) of Epon-embedded cells. The fluorescent intensity of most fluorescent proteins, is significantly weakened during post-fixation using osmium tetroxide, dehydration, and Epon embedding These preparations are essential in order to preserve the membranous structures

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