Backscattered electron image of osmium-impregnated/macerated tissues as a novel technique for identifying the cis -face of the Golgi apparatus by high-resolution scanning electron microscopy

The Regulated Secretion and Models of Intracellular Transport: The Goblet Cell as an Example

Transport models are extremely important to map thousands of proteins and their interactions inside a cell. The transport pathways of luminal and at least initially soluble secretory proteins synthesized in the endoplasmic reticulum can be divided into two groups: the so-called constitutive secretory pathway and regulated secretion (RS) pathway, in which the RS proteins pass through the Golgi complex and are accumulated into storage/secretion granules (SGs). Their contents are released when stimuli trigger the fusion of SGs with the plasma membrane (PM). In specialized exocrine, endocrine, and nerve cells, the RS proteins pass through the baso-lateral plasmalemma. In polarized cells, the RS proteins secrete through the apical PM. This exocytosis of the RS proteins increases in response to external stimuli. Here, we analyze RS in goblet cells to try to understand the transport model that can be used for the explanation of the literature data related to the intracellular transport of their mucins.

Algorithm for Modern Electron Microscopic Examination of the Golgi Complex

The Golgi complex (GC) is an essential organelle of the eukaryotic exocytic pathway. It has a very complexed structure and thus localization of its resident proteins is not trivial. Fast development of microscopic methods generates a huge difficulty for Golgi researchers to select the best protocol to use. Modern methods of light microscopy, such as super-resolution light microscopy (SRLM) and electron microscopy (EM), open new possibilities in analysis of various biological structures at organelle, cell, and organ levels. Nowadays, new generation of EM methods became available for the study of the GC; these include three-dimensional EM (3DEM), correlative light-EM (CLEM), immune EM, and new estimators within stereology that allow realization of maximal goal of any morphological study, namely, to achieve a three-dimensional model of the sample with optimal level of resolution and quantitative determination of its chemical composition. Methods of 3DEM have partially overlapping capabilities. This requires a careful comparison of these methods, identification of their strengths and weaknesses, and formulation of recommendations for their application to cell or tissue samples. Here, we present an overview of 3DEM methods for the study of the GC and some basics for how the images are formed and how the image quality can be improved.

Applications of Scanning Electron Microscopy Using Secondary and Backscattered Electron Signals in Neural Structure

Scanning electron microscopy (SEM) has contributed to elucidating the ultrastructure of bio-specimens in three dimensions. SEM imagery detects several kinds of signals, of which secondary electrons (SEs) and backscattered electrons (BSEs) are the main electrons used in biological and biomedical research. SE and BSE signals provide a three-dimensional (3D) surface topography and information on the composition of specimens, respectively. Among the various sample preparation techniques for SE-mode SEM, the osmium maceration method is the only approach for examining the subcellular structure that does not require any reconstruction processes. The 3D ultrastructure of organelles, such as the Golgi apparatus, mitochondria, and endoplasmic reticulum has been uncovered using high-resolution SEM of osmium-macerated tissues. Recent instrumental advances in scanning electron microscopes have broadened the applications of SEM for examining bio-specimens and enabled imaging of resin-embedded tissue blocks and sections using BSE-mode SEM under low-accelerating voltages; such techniques are fundamental to the 3D-SEM methods that are now known as focused ion-beam SEM, serial block-face SEM, and array tomography (i.e., serial section SEM). This technical breakthrough has allowed us to establish an innovative BSE imaging technique called section-face imaging to acquire ultrathin information from resin-embedded tissue sections. In contrast, serial section SEM is a modern 3D imaging technique for creating 3D surface rendering models of cells and organelles from tomographic BSE images of consecutive ultrathin sections embedded in resin. In this article, we introduce our related SEM techniques that use SE and BSE signals, such as the osmium maceration method, semithin section SEM (section-face imaging of resin-embedded semithin sections), section-face imaging for correlative light and SEM, and serial section SEM, to summarize their applications to neural structure and discuss the future possibilities and directions for these methods.

Optimizing the reaction temperature to facilitate an efficient osmium maceration procedure

The osmium maceration method is a powerful technique for observing the three-dimensional ultrastructure of cellular organelles by scanning electron microscopy. In the conventional osmium maceration method, tissues are immersed in a diluted osmium tetroxide solution for several days at 20°C to remove soluble cytosolic proteins from the freeze-cracked surface of cells, and the optimal duration of this process is dependent on the cell type. To improve the efficiency of the osmium maceration procedure, we have examined systematically the relationship between the reaction temperature and time of the osmium maceration procedure. Treatment at temperatures higher than 20°C drastically shortened the time required to remove cytosolic proteins from the freeze-cracked surface of specimens with optimal durations for the osmium maceration of hepatocytes at 30, 40, 50 and 60°C being 30, 15, 5 and 1 h, respectively. Considering the stability and reproducibility of the macerated specimens, we concluded that the most appropriate temperature was 30 to 40°C. This rapid osmium maceration procedure was used successfully to observe the 3D ultrastructure of Purkinje cells in the cerebellum and proximal convoluted tubule cells in the kidney. This simple and reproducible rapid osmium maceration protocol should find wide appeal for the 3D analysis of cellular organelles in various cell types.

Three-dimensional morphology of the Golgi apparatus in osteoclasts: NADPase and arylsulfatase cytochemistry, and scanning electron microscopy using osmium maceration

This study was designed to observe osteoclasts in the rat femora by light and electron microscopic cytochemistry for nicotinamide adenine dinucleotide phosphatase (NADPase) and arylsulfatase, and scanning electron microscopy using osmium maceration to assess the three-dimensional morphology of the Golgi apparatus in osteoclasts. The Golgi apparatus showed strong NADPase activity and surrounded each nucleus with the cis-side facing the nucleus. The Golgi apparatus could be often traced for a length of 20 μm or longer. Observations of serial semi-thin sections confirmed that a single line of reaction products (=lead precipitates) intervened somewhere between any two neighboring nuclei. The nuclear membrane showed strong arylsulfatase activity as well as rough endoplasmic reticulum and lysosomes. Scanning electron microscopy showed that the Golgi apparatus covered the nucleus in a porous sheet-like configuration. Under magnification, the cis-most saccule showed a sieve-like configuration with fine fenestrations. The saccules decreased fenestration numbers toward the trans-side and displayed a more plate-like appearance. The above findings indicate the following. (1) The Golgi saccules of osteoclasts have a three-dimensional structure comparable with that generally seen in other cell types. (2) The Golgi apparatus forms a porous multi-spherical structure around nuclei. Within the structure, in most cases a Golgi stack partitions the room into several compartments in each of which a nucleus fits. (3) The nuclear membrane synthesizes some kinds of proteins more stably and sufficiently than the rough endoplasmic reticulum. Consequently, the Golgi apparatus accumulates around nuclei with the cis-side facing the nucleus.

Golgi apparatus dis- and reorganizations studied with the aid of 2-deoxy-D-glucose and visualized by 3D-electron tomography

We studied Golgi apparatus disorganizations and reorganizations in human HepG2 hepatoblastoma cells by using the nonmetabolizable glucose analogue 2-deoxy-d-glucose (2DG) and analyzing the changes in Golgi stack architectures by 3D-electron tomography. Golgi stacks remodel in response to 2DG-treatment and are replaced by tubulo-glomerular Golgi bodies, from which mini-Golgi stacks emerge again after removal of 2DG. The Golgi stack changes correlate with the measured ATP-values. Our findings indicate that the classic Golgi stack architecture is impeded, while cells are under the influence of 2DG at constantly low ATP-levels, but the Golgi apparatus is maintained in forms of the Golgi bodies and Golgi stacks can be rebuilt as soon as 2DG is removed. The 3D-electron microscopic results highlight connecting regions that interlink membrane compartments in all phases of Golgi stack reorganizations and show that the compact Golgi bodies mainly consist of continuous intertwined tubules. Connections and continuities point to possible new transport pathways that could substitute for other modes of traffic. The changing architectures visualized in this work reflect Golgi stack dynamics that may be essential for basic cell physiologic and pathologic processes and help to learn, how cells respond to conditions of stress.