Localization of acid phosphatase activity in hepatic lysosomes by means of electron microscopy

Over Fifty Years of Life, Death, and Cannibalism: A Historical Recollection of Apoptosis and Autophagy

Research in biomedical sciences has changed dramatically over the past fifty years. There is no doubt that the discovery of apoptosis and autophagy as two highly synchronized and regulated mechanisms in cellular homeostasis are among the most important discoveries in these decades. Along with the advancement in molecular biology, identifying the genetic players in apoptosis and autophagy has shed light on our understanding of their function in physiological and pathological conditions. In this review, we first describe the history of key discoveries in apoptosis with a molecular insight and continue with apoptosis pathways and their regulation. We touch upon the role of apoptosis in human health and its malfunction in several diseases. We discuss the path to the morphological and molecular discovery of autophagy. Moreover, we dive deep into the precise regulation of autophagy and recent findings from basic research to clinical applications of autophagy modulation in human health and illnesses and the available therapies for many diseases caused by impaired autophagy. We conclude with the exciting crosstalk between apoptosis and autophagy, from the early discoveries to recent findings.

Gaucher disease: achievements and prospects

Gaucher disease (GD) is the most common lysosomal storage disorder, resulting from a deficiency in the activity of a lysosomal enzyme glucocerebrosidase, which is involved in the catabolism of sphingolipids. The phenomenal progress in understanding the pathogenesis and development of specific therapy of this disease over the past 60 years dramatically changed the clinical phenotype of GD, turning a severe progressive disorder into an asymptomatic metabolic defect. The evolution of the understanding of GD associated with fundamental discoveries in the field of cell biology, biochemistry and genetics may be of interest to a wide audience as a model of the effective work of the scientific community in the treatment of rare metabolic pathology.

Podocyte Lysosome Dysfunction in Chronic Glomerular Diseases

Podocytes are visceral epithelial cells covering the outer surface of glomerular capillaries in the kidney. Blood is filtered through the slit diaphragm of podocytes to form urine. The functional and structural integrity of podocytes is essential for the normal function of the kidney. As a membrane-bound organelle, lysosomes are responsible for the degradation of molecules via hydrolytic enzymes. In addition to its degradative properties, recent studies have revealed that lysosomes may serve as a platform mediating cellular signaling in different types of cells. In the last decade, increasing evidence has revealed that the normal function of the lysosome is important for the maintenance of podocyte homeostasis. Podocytes have no ability to proliferate under most pathological conditions; therefore, lysosome-dependent autophagic flux is critical for podocyte survival. In addition, new insights into the pathogenic role of lysosome and associated signaling in podocyte injury and chronic kidney disease have recently emerged. Targeting lysosomal functions or signaling pathways are considered potential therapeutic strategies for some chronic glomerular diseases. This review briefly summarizes current evidence demonstrating the regulation of lysosomal function and signaling mechanisms as well as the canonical and noncanonical roles of podocyte lysosome dysfunction in the development of chronic glomerular diseases and associated therapeutic strategies.

A lysosome-targeted near-infrared fluorescent probe for imaging of acid phosphatase in living cells

Fluorescent probes for the detection of acid phosphatases (ACP) are important in the investigation of the pathology and diagnosis of diseases. We reported a lysosome-targeted near-infrared (NIR) fluorescent probe SHCy-P based on a novel NIR-emitting thioxanthene-indolium dye for the detection of ACP. The probe showed a long wavelength fluorescence emission at λ_em = 765 nm. Due to the ACP-catalyzed cleavage of the phosphate group in SHCy-P, the probe exhibited high selectivity and sensitivity for the 'turn-on' detection of ACP with a limit of detection as low as 0.48 U L^-1. The probe SHCy-P could also be used to detect and image endogenous ACP in lysosomes. In light of these prominent properties, we envision that SHCy-P will be an efficient optical imaging approach for investigating the ACP activity in disease diagnosis.

Autophagy in hepatic adaptation to stress

Autophagy is an evolutionarily ancient process whereby eukaryotic cells eliminate disposable or potentially dangerous cytoplasmic material, to support bioenergetic metabolism and adapt to stress. Accumulating evidence indicates that autophagy operates as a critical quality control mechanism for the maintenance of hepatic homeostasis in both parenchymal (hepatocytes) and non-parenchymal (stellate cells, sinusoidal endothelial cells, Kupffer cells) compartments. In line with this notion, insufficient autophagy has been aetiologically involved in the pathogenesis of multiple liver disorders, including alpha-1-antitrypsin deficiency, Wilson disease, non-alcoholic steatohepatitis, liver fibrosis and hepatocellular carcinoma. Here, we critically discuss the importance of functional autophagy for hepatic physiology, as well as the mechanisms whereby defects in autophagy cause liver disease.

Chaperone-Mediated Autophagy in the Liver: Good or Bad?

Hepatitis C virus (HCV) infection triggers autophagy processes, which help clear out the dysfunctional viral and cellular components that would otherwise inhibit the virus replication. Increased cellular autophagy may kill the infected cell and terminate the infection without proper regulation. The mechanism of autophagy regulation during liver disease progression in HCV infection is unclear. The autophagy research has gained a lot of attention recently since autophagy impairment is associated with the development of hepatocellular carcinoma (HCC). Macroautophagy, microautophagy, and chaperone-mediated autophagy (CMA) are three autophagy processes involved in the lysosomal degradation and extracellular release of cytosolic cargoes under excessive stress. Autophagy processes compensate for each other during extreme endoplasmic reticulum (ER) stress to promote host and microbe survival as well as HCC development in the highly stressed microenvironment of the cirrhotic liver. This review describes the molecular details of how excessive cellular stress generated during HCV infection activates CMA to improve cell survival. The pathological implications of stress-related CMA activation resulting in the loss of hepatic innate immunity and tumor suppressors, which are most often observed among cirrhotic patients with HCC, are discussed. The oncogenic cell programming through autophagy regulation initiated by a cytoplasmic virus may facilitate our understanding of HCC mechanisms related to non-viral etiologies and metabolic conditions such as uncontrolled type II diabetes. We propose that a better understanding of how excessive cellular stress leads to cancer through autophagy modulation may allow therapeutic development and early detection of HCC.

Reconfigurable Bioinspired Framework Nucleic Acid Nanoplatform Dynamically Manipulated in Living Cells for Subcellular Imaging

In nature, the formation of spider silk fibers begins with dimerizing the pH-sensitive N-terminal domains of silk proteins (spidroins) upon lowering pH, and provides a natural masterpiece for programmable assembly. Inspired by the similarity of pH-dependent dimerization behaviors, introduced here is an i-motif-guided model to mimic the initial step of spidroin assembly at the subcellular level. A framework nucleic acid (FNA) nanoplatform is designed using two tetrahedral DNA nanostructures (TDNs) with different branched vertexes carrying a bimolecular i-motif and a split ATP aptamer. Once TDNs enter acidic lysosomes within living cells, they assemble into a heterodimeric architecture, thereby enabling the formation of a larger-size framework and meanwhile subcellular imaging in response to endogenous ATP, which can be dynamically manipulated by adjusting intracellular pH and ATP levels with external drug stimuli.

Lysosome: The metabolic signaling hub

For the past five decades, the lysosome has been characterized as an unglamorous cellular recycling center. This notion has undergone a radical shift in the last 10 years, with new research revealing that this organelle serves as a major hub for metabolic signaling pathways. The discovery that master growth regulators, including the protein kinase mTOR (mechanistic target of rapamycin), make their home at the lysosomal surface has generated intense interest in the lysosome's key role in nutrient sensing and cellular homeostasis. The transcriptional networks required for lysosomal maintenance and function are just being unraveled and their connection to lysosome-based signaling pathways revealed. The catabolic and anabolic pathways that converge on the lysosome connect this organelle with multiple facets of cellular function; when these pathways are deregulated they underlie multiple human diseases, and promote cellular and organismal aging. Thus, understanding how lysosome-based signaling pathways function will not only illuminate the fascinating biology of this organelle but will also be critical in unlocking its therapeutic potentials.

Astroglial vesicular network: evolutionary trends, physiology and pathophysiology

Intracellular organelles, including secretory vesicles, emerged when eukaryotic cells evolved some 3 billion years ago. The primordial organelles that evolved in Archaea were similar to endolysosomes, which developed, arguably, for specific metabolic tasks, including uptake, metabolic processing, storage and disposal of molecules. In comparison with prokaryotes, cell volume of eukaryotes increased by several orders of magnitude and vesicle traffic emerged to allow for communication between distant intracellular locations. Lysosomes, first described in 1955, a prominent intermediate of endo- and exocytotic pathways, operate virtually in all eukaryotic cells including astroglia, the most heterogeneous type of homeostatic glia in the central nervous system. Astrocytes support neuronal network activity in particular through elaborated secretion, based on a complex intracellular vesicle network dynamics. Deranged homeostasis underlies disease and astroglial vesicle traffic contributes to the pathophysiology of neurodegenerative (Alzheimer's disease, Huntington's disease), neurodevelopmental diseases (intellectual deficiency, Rett's disease) and neuroinfectious (Zika virus) disorders. This review addresses astroglial cell-autonomous vesicular traffic network, as well as its into primary and secondary vesicular network defects in diseases, and considers this network as a target for developing new therapies for neurological conditions.

Autophagy in the liver: functions in health and disease

The concept of macroautophagy was established in 1963, soon after the discovery of lysosomes in rat liver. Over the 50 years since, studies of liver autophagy have produced many important findings. The liver is rich in lysosomes and possesses high levels of metabolic-stress-induced autophagy, which is precisely regulated by concentrations of hormones and amino acids. Liver autophagy provides starved cells with amino acids, glucose and free fatty acids for use in energy production and synthesis of new macromolecules, and also controls the quality and quantity of organelles such as mitochondria. Although the efforts of early investigators contributed markedly to our current knowledge of autophagy, the identification of autophagy-related genes represented a revolutionary breakthrough in our understanding of the physiological roles of autophagy in the liver. A growing body of evidence has shown that liver autophagy contributes to basic hepatic functions, including glycogenolysis, gluconeogenesis and β-oxidation, through selective turnover of specific cargos controlled by a series of transcription factors. In this Review, we outline the history of liver autophagy study, and then describe the roles of autophagy in hepatic metabolism under healthy and disease conditions, including the involvement of autophagy in α1-antitrypsin deficiency, NAFLD, hepatocellular carcinoma and viral hepatitis.

Studies on secretory activity in the pars intermedia of Xenopus laevis 2: A biochemical and electron cytochemical investigation of acid hydrolase activity following the stimulation of secretory activity in vivo

In the MSH cell at the onset of secretory activity, acid hydrolase activity increases. This increased activity, shown quantitatively by assaying beta-glycerophosphatase and R-glucuronidase within the stimulated gland, has been shown by electron cytochemical methods for beta-glycerophosphatase (acid phosphatase) and aryl sulphatase to be related to the production of large numbers of dense bodies. Cytochemical evidence also supports the view that these lytic bodies arise from GERL-like cisternal elements since it is shown that in addition to the flattened, parallel Golgi cisternae these elements are also R-glycerophosphatase-positive. The similarities between the dense bodies and those of other cell types are described and discussed.

CYTOLOGICAL STUDIES ON TWO FUNCTIONAL HEPATOMAS : Interrelations of Endoplasmic Reticulum, Golgi Apparatus, and Lysosomes

The Reuber hepatoma H-35 and Morris hepatoma 5123 have been studied by electron microscopy and by cytochemical staining methods for a number of phosphatases. These studies emphasize the resemblances of the two tumors to rat liver, but they also indicate distinctive features in each of the three tissues. Secretory product accumulates within the cisternae of the Golgi apparatus that dilate to form the Golgi vacuoles. The vacuoles apparently separate, and secretory material undergoes further condensation within them. These "secretory vacuoles" possess acid phosphatase activity and may thus be considered lysosomes. The membranes of the Golgi apparatus are without acid phosphatase activity but show high levels of thiaminepyrophosphatase activity. The endoplasmic reticulum also hydrolyzes thiaminepyrophosphate but at a lower rate; it hydrolyzes the diphosphates of uridine, guanosine, and inosine rapidly. These observations and the electron microscopic images are consistent with the view that the cytomembranes are in a dynamic state of flux, movement, and transformation in the living cell, and that smooth surfaced derivatives of the endoplasmic reticulum become refashioned into the Golgi membranes as the Golgi membranes are being refashioned into those that delimit secretory vacuoles. The variations encountered in the two hepatomas are described. The electron microscope literature dealing with the relations of the Golgi apparatus to secretory granules, on the one hand, and the endoplasmic reticulum, on the other, is reviewed briefly.

LOCALIZATION OF ADENOSINE TRIPHOSPHATASE ACTIVITY IN THE RAT SPERM TAIL AS REVEALED BY ELECTRON MICROSCOPY

The epididymides of rat testis were fixed in glutaraldehyde and cut as frozen sections. The sections were incubated in lead nitrate solution containing as a substrate either ATP, AMP, creatinine phosphate, beta glycerophosphate, or phenyl phosphate. Then they were postfixed in osmium tetroxide, embedded, sectioned, and examined with the electron microscope. In the sperm tail, when ATP is used as a substrate the reaction product (lead phosphate) is observed both in the tail filament complex and on the surface membrane of the mitochondrial helix of the middle piece. In the tail filament complex, this product is seen near the nine paired peripheral and two central filaments, and in the matrix between the outer coarse fibers. But the product is not observed within these filaments and fibers. In longitudinal sections, no periodicity of the deposits in the complex is observed. When the other phosphate compounds are used as substrates the reaction products appear on the surface membrane of the mitochondrial helix, and are not found in the tail filament complex. No distinctly different localization of the reaction products is observed when substrates other than ATP are used. Possible relationships between the structure and the function of the sperm tail are discussed in the light of these findings.

The role of glucocerebrosidase mutations in Parkinson disease and Lewy body disorders

Mutations in the gene encoding glucocerebrosidase (GBA), the enzyme deficient in the lysosomal storage disorder Gaucher disease, are associated with the development of Parkinson disease and other Lewy body disorders. In fact, GBA variants are currently the most common genetic risk factor associated with parkinsonism, and identified subjects with Parkinson disease are more than five times more likely to carry mutations in GBA. The mechanisms underlying this association are not known, but proposed theories include enhanced protein aggregation, alterations in lipid levels, and autophagy-lysosomal dysfunction promoting the retention of undegraded proteins. We review the genetic studies linking GBA to parkinsonism, as well as several of the mechanisms postulated to explain the association of GBA mutations and the synucleinopathies, which demonstrate how studies of a rare mendelian disease may provide insights into our understanding of a common complex disorder.

Intracellular membrane traffic at high resolution

Membrane traffic between organelles is essential for a multitude of processes that maintain cell homeostasis. Many steps in these tightly regulated trafficking pathways take place in microdomains on the membranes of organelles, which require analysis at nanometer resolution. Electron microscopy (EM) can visualize these processes in detail and is mainly responsible for our current view of morphology on the subcellular level. This review discusses how EM can be applied to solve many questions of intracellular membrane traffic, with a focus on the endosomal system. We describe the expansion of the technique from purely morphological analysis to cryo-immuno-EM, correlative light electron microscopy (CLEM), and 3D electron tomography. In this review we go into some technical details of these various techniques. Furthermore, we provide a full protocol for immunolabeling on Lowicryl sections of high-pressure frozen cells as well as a detailed description of a simple CLEM method that can be applied to answer many membrane trafficking questions. We believe that these EM-based techniques are important tools to expand our understanding of the molecular details of endosomal sorting and intracellular membrane traffic in general.

Acid phosphatase activity may affect the tuber swelling by partially regulating sucrose-mediated sugar resorption in potato

APase activity is involved in regulating many physiological and developmental events by affecting the resorption process. In this study, we investigate the role of APase activity in tuber development in potato. APase activities were mainly localized in cytoplasm, gaps among cells and stroma of amyloplasts of parenchyma cells at the stage of tuber swelling. AP1, encoding a putative APase, was also highly expressed in swelling tubers and a low level of expression was observed in elongated stolons and matured tubers. Inhibition of APase activity by applying Brefeldin A, an inhibitor of APase production and secretion, significantly suppressed the tuber swelling and moderately affected the stolon elongation and the tuberization frequency. During tuber development, sucrose serves as the main soluble sugar for long-distance transportation and resorption. Moreover, inhibition of APase activity by Brefeldin A markedly reduced the sucrose content in tubers and further decreased the starch accumulation, suggesting that the function of APase in regulating the tuber swelling might be at least partially mediated by the sugar resorption. Exogenous sucrose treatments further indicate the important role of sucrose-mediated sugar resorption in tuber swelling. These results suggest that the APase activity might affect the tuber swelling by partially regulating the sucrose-mediated sugar resorption.

Imaging and imagination: understanding the endo-lysosomal system

Lysosomes are specialized compartments for the degradation of endocytosed and intracellular material and essential regulators of cellular homeostasis. The importance of lysosomes is illustrated by the rapidly growing number of human disorders related to a defect in lysosomal functioning. Here, we review current insights in the mechanisms of lysosome biogenesis and protein sorting within the endo-lysosomal system. We present increasing evidence for the existence of parallel pathways for the delivery of newly synthesized lysosomal proteins directly from the trans-Golgi network (TGN) to the endo-lysosomal system. These pathways are either dependent or independent of mannose 6-phosphate receptors and likely involve multiple exits for lysosomal proteins from the TGN. In addition, we discuss the different endosomal intermediates and subdomains that are involved in sorting of endocytosed cargo. Throughout our review, we highlight some examples in the literature showing how imaging, especially electron microscopy, has made major contributions to our understanding of the endo-lysosomal system today.

The fine structural localization of adenosine triphosphatase in the small intestine, kidney, and liver of the rat

The distribution of the reaction product of a staining method for adenosine triphosphatase (ATPase) in rat small intestine, kidney, and liver was studied with electron microscopy. Several procedures were tried but the best results were obtained from tissue that had been quenched in liquid nitrogen, sectioned at 25 µ in a cryostat, fixed for 30 to 90 minutes at 4°C in formalin-sucrose buffered to pH 7.2, incubated with substrate, and then osmicated and prepared for electron microscopy in the usual way. This procedure enabled the localization of mitochondrial ATPase to be studied. In tissue fixed in small blocks in osmium tetroxide for 3 minutes prior to incubation with substrate, good preservation was noted, and the reaction product for ATPase was localized on the cell membrane and nuclei. The reaction product was present in abundant amount in the nuclei, and particularly within nucleoli, of all tissues studied. Because the histochemical localization of nuclear enzymes poses numerous interpretative problems at the present time, the significance of this nuclear localization is uncertain. Cell (plasma) membranes were the site of localization, especially at areas where it has been proposed that active transport mechanisms may occur, namely, on the microvilli of intestinal epithelium, endothelial lining of capillaries, glomerular epithelial cell membranes, basal infoldings of the cell membrane of renal tubules, on the microvilli of bile canaliculi, and on the microvilli of proximal convoluted tubular epithelial cells. ATPase localization on the cristae mitochondriales was also demonstrated.

Cytochemical and electron microscopic studies of rat liver with reduced capacity to transport conjugated bilirubin

Although the livers of rats treated with agents known to suppress bilirubin transport appeared relatively normal on routine histological sections, cytochemical and electron microscopic preparations revealed marked changes in: (a) levels of alkaline phosphatase and apparent ATPase activities of the cell membrane at the sinusoids, bile canaliculi, and between adjacent cells; (b) morphology of the bile canaliculi such as dilatation, fragmentation, vesiculation and reduced numbers of microvilli; (c) the number of lysosomes and their distribution within the cell. Similar changes in the cytochemistry of the liver cell were induced by extrahepatic obstruction.

The localization of acid phosphatase in rat liver cells as revealed by combined cytochemical staining and electron microscopy

Discrete localization of stain in pericanalicular granules was found in 10 µ frozen sections of formol-phosphate-sucrose-fixed liver stained by the Gomori acid phosphatase technique and examined in the light microscope. The staining patterns, before and after treatment with Triton X-100 and lecithinase, were identical with those previously reported for formol-calcium-fixed material treated in the same way, and it can be assumed that the stained granules are identical with "lysosomes." Examination in the light microscope of the staining patterns and lead penetration in fixed blocks and slices of various dimensions showed nuclear staining and other artefacts to be present, produced by the different rates of penetration of the various components of the staining medium into the tissue. A uniform pericanalicular staining pattern could be obtained, however, with slices not more than 50 µ thick, into which the staining medium could penetrate rapidly from both faces. The staining pattern produced in 50 µ slices was the same both at pH 5.0 and pH 6.2, and was not altered by subsequent embedding of the stained material in butyl methacrylate. Electron microscopy showed the fine structure of fixed 50 µ frozen slices to be well preserved, but it deteriorated badly when they were incubated in the normal Gomori medium at pH 5.0 before postfixing in osmium tetroxide. After incubation in the Gomori medium at pH 6.2, the detailed morphology was substantially maintained. In both cases lead phosphate, the reaction product, was found in the pericanalicular regions of the cell, but only in the vacuolated dense bodies and never in the microbodies. Not every vacuolated dense body contained lead, and stained and unstained bodies were sometimes seen adjacent to each other. This heterogeneous distribution of stain within a morphologically homogeneous group of particles is consistent with de Duve's suggestion (9) that there is a heterogeneous distribution of enzymes within the lysosome population. It is concluded from these investigations that the vacuolated dense bodies seen in the electron microscope are the morphological counterparts of the "lysosomes" defined biochemically by de Duve.

Electron microscopic study of the ATPase activity of the BAI strain A (myeloblastosis) avian tumor virus

Thymus glands of chicks with leukemia induced by BAI strain A (myeloblastosis) virus were fixed in cold 4 per cent formaldehyde-sucrose. Frozen sections were incubated in the ATPase medium of Wachstein and Meisel and studied by light microscopy and electron microscopy. The ATPase activity of the virus is localized to the outermost membrane of the virus. The membrane of the blast-like cells of the thymus cortex from which the virus emerges, by budding, also possesses such activity. It appears likely that the outermost membrane of the virus is derived from the plasma membrane of these cells.

Electron microscopy of lysosome-rich fractions from rat thymus isolated by density-gradient centrifugation before and after whole-body x-irradiation

Fractions from rat thymuses were isolated by sucrose density-gradient centrifugation, before and after 1000 r whole-body x-irradiation, and examined by electron microscopy. Cytochrome oxidase and acid phosphatase activities of these fractions were tested as well. Electron-opaque bodies with diameters ranging from 0.10 to 0.35 µ, with a mean of 0.25 µ, were found in fractions having high acid phosphatase activity, while the fractions rich in cytochrome oxidase consisted mostly of mitochondria. After irradiation, there was an increased ratio of dense bodies to mitochondria. These particles are considered to be lysosomes similar to those identified in other rat tissues. Their relationship to the mitochondria is discussed.

Age-related changes in the inner zone of the adrenal cortex of the rat--a morphologic and biochemical study

In this work, a correlative morphologic and biochemical study on the effects of ageing on the rat adrenal Inner Zone (IZ) was made. Male Wistar rats were studied at 2, 6, 12, 18 and 24 months. Structural data of Zona Fasciculata (ZF) showed age-related increase in cell volume (P < 0.05), decrease in mitochondria (P < 0.01) and smooth endoplasmic reticulum (SER) volumes, and increase in lipid droplets (P < 0.01) and lipofuscin granules (P < 0.01) volumes. In Zona Reticularis, the main change observed was the increase in lipofuscin granules (P < 0.001). Serum corticosterone from unstimulated rats increased until 12 months but decreased thereafter (P < 0.01), to levels below those from 2-month-old rats. Similarly, plasma adrenocorticotrophic hormone (ACTH) presented a maximum at 12 months, followed by a decrease to levels higher than at 2 months (P < 0.05). In rats injected either with only ACTH or dexamethasone, before ACTH stimulation, corticosterone level had a maximum at 12 months. In aged rats, serum high density lipoprotein (HDL) and adrenal cholesterol ester increased significantly (P < 0.05 and P < 0.01, respectively), whereas adrenal corticosterone decreased. Products of lipid peroxidation, assayed with the thiobarbituric acid reaction and fluorimetry showed an age-related increase (P < 0.05). The age-related decrease in mitochondria and SER volumes is consistent with the decrease of serum corticosterone. The increase in lipid droplet and HDL and the reduction of adrenal corticosterone level correlate with the increase of adrenal cholesterol ester content. These suggest a continued uptake of steroid precursor but a reduced steroid synthesis. On the whole, the data provide evidence for an age-related reduced functional ability of IZ and particularly of ZF.

FINE STRUCTURAL CHANGES IN THE INTESTINAL EPITHELIUM OF THE BULLFROG DURING METAMORPHOSIS

The fine structural changes occurring in the columnar absorbing cells of the intestinal epithelium during metamorphosis of the bullfrog, Rana catesbeiana, have been examined by phase contrast and electron microscopy. Tissue samples taken just posterior to the entrance of the hepatopancreatic duct were fixed in veronal acetate-buffered osmium tetroxide and embedded in methacrylate. Under the action of the metamorphic stimulus (thyroid hormone), specific and characteristic responses were given by differentiated larval cells and undifferentiated basal cells within the same epithelium. The functional larval cells underwent degenerative changes and were retained for a time within the metamorphosing epithelium. Dense bodies appeared and increased in number in association with the loss of normal cell structure. Because of their morphology and time of formation, these bodies have been tentatively identified as lysosomes. Early in metamorphosis the basal cells did not change, but they subsequently proliferated to form a new cell layer beneath the remaining degenerating cells that lined the lumen. After the dying cells were sloughed into the gut, the new epithelium differentiated to form the adult tissue. The columnar epithelial cells of the mature animal differed in their fine structural organization from their larval precursors. Therefore, their adult configuration was molded by the action of the metamorphic stimulus.

STUDIES ON ISOLATED CELL COMPONENTS. XVI. THE DISTRIBUTION OF ACID PHENYL PHOSPHATASE ACTIVITIES IN RAT LIVER BREI FRACTIONATED IN THE ZONAL ULTRACENTRIFUGE

The zonal ultracentrifuge has been used to separate the major components of rat liver brei (soluble phase, ribosomes, microsomes, mitochondria, membranous fragments, and nuclei) during one centrifugation, by using a 1200 ml sucrose gradient varying linearly with radius from 17 to 55 per cent (w/w) with a "cushion" of 66 per cent sucrose at the rotor edge at speeds up to 30,000 RPM. Liver brei was found to contain a family of phosphatases (phenol disodium phosphate substrate, sodium malonate buffers and Turgitol NPX, a non-ionic detergent). Activity maxima at pH 4.1 and 5.9 were observed in untreated brei prepared in 0.25 M sucrose. The addition of the non-ionic detergent Turgitol NPX selectively caused the release of considerable additional activity between these optima. The activity measured at pH 4.1 was primarily associated with the cytoplasmic granules, while the activities at pH 4.8, 5.4 and 5.9 were found in both soluble phase and particulate-mitochondria and membranous fractions. The activities present beyond the region of the gradient occupied by the soluble phase (sample layer) were all bound to particles sedimentable at 105,536 g (average) in the preparative ultracentrifuge. The data suggest that the different activities are not similarly distributed between soluble phase and particulate fractions. When the data are expressed in terms of specific activity, the area in the gradient between the microsomes and mitochondria now appears richest in all the acid phenyl phosphatase activities measured, while the soluble phase and larger particulate fractions appear relatively poor in activity. This part of the gradient is occupied by small, dense granules which may be the so called lysosomes. Pretreatment of the brei with Turgitol NPX prior to fractionation in the zonal ultracentrifuge resulted in the solubilization of acid phenyl phosphatase activities (almost all the activity was in the sample zone of the gradient) and the non-specific destruction of the formed elements of the brei. Essentially all of the activities present in the original brei measured under these conditions were recovered after zonal ultracentrifuge fractionations.

LYTIC ACTIVITIES IN RENAL PROTEIN ABSORPTION DROPLETS. AN ELECTRON MICROSCOPICAL CYTOCHEMICAL STUDY

The digestive cycle following reabsorption of hemoglobin by cells of the proximal convoluted tubules in mouse kidney and the uptake of ferritin by glomerular mesangial cells in the kidney of normal and nephrotic rats were investigated by electron microscopical histochemical procedures. Mouse kidneys, sampled at closely spaced time points between 1 to 48 hours after intraperitoneal injection of hemoglobin, and rat (normal and nephrotic) kidneys, sampled at 30 minutes, 2 hours, and 48 hours after intravenous injection of ferritin, were fixed in glutaraldehyde, cut at 50 µ on a freezing microtome, incubated for acid phosphatase and thiolacetate-esterase, and postfixed in OsO₄. Satisfactory preservation of fine structure permitted the localization of the enzymatic reaction products on cell structures involved in uptake and digestion of exogenous proteins. The latter were identified either by their density (hemoglobin) or their molecular structure (ferritin). It was found that lysosomal enzymic activities and incorporated exogenous proteins occur together in the same membrane-bounded structures. In the cells of the proximal convolution, lytic activities become demonstrable within 1 hour after hemoglobin injection, appear first in apical vacuoles filled with hemoglobin, and persist in fully formed protein absorption droplets. At the end of the lytic cycle (∼48 hours post injection), the cells have an increased population of polymorphic bodies which exhibit lytic activities. In smaller numbers, identical bodies occur in controls. It is concluded that they represent remnants of previous digestive events. The means by which the resorptive vacuoles acquire hydrolytic activities remain unknown. Fusion of newly formed vacuoles with residual bodies was not seen, and hemoglobin incorporation into such bodies was only occasionally encountered. Acid phosphatase activity was found sometimes in the Golgi complex, but enzyme transport from the complex to the resorbing vacuoles could not be established. Autolytic vacuoles containing mitochondria or mitochondrial remnants were frequently found during the early stages of hemoglobin resorption, but no definite conclusions about the mechanism involved in the segregation of endogenous material were obtained. In nephrotic rats ferritin was segregated in membrane-bounded bodies mainly in the mesangial cells and to a lesser extent in epithelial and endothelial cells. Most of these sites were marked by the reaction products of acid phosphatase and organophosphorus-resistant esterase and therefore identified as lysosomes connected with the digestion of incorporated exogenous proteins.

Studies on experimental chlamydial mastitis in goat histoenzymology

Two strains of Chlamydia psittaci (one isolated from aborted goat foetus and the other from brain of a buffalo calf that had died of meningoencephalitis) were injected intracisternally into six goats to produce experimental mastitis. Cryostat sections of 7-8 microns thickness, obtained from udder, teat, liver and kidney of infected and control animals were incubated for histoenzymic demonstration of alkaline-(AKPase), acid-(ACPase) and adenosine-tri-(ATPase) phosphatases; lactate-(LDH) and succinate-(SDH) dehydrogenases and for reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-D). Results demonstrated that AKPase and NADPH-D declined while ACPase accumulated in acinar cells of udder while both NADPH-D and ACPase decreased in teat sinus epithelium. Hepatic canaliculi in perilobular areas of liver lobules registered complete absence of AKPase and ATPase. Hepatocytes and renal tubules accumulated LDH, SDH and NADPH-D. The interstitial connective tissue of udder and kidney presented higher levels of AKPase. Comparison of results with biochemical alterations in the level of these enzymes revealed striking discrepancies which seem to arise because of failure of biochemical procedures to discriminate between functional cells of tissue and inflammatory cells. The functional significance of histoenzymic alterations has been discussed.

Histochemical and ultrastructural observations on brown degeneration of human intervertebral disc

Thirty-eight fresh human intervertebral discs collected during anterior interbody fusion surgery were histochemically and ultrastructurally analyzed for pigments. Macroscopically, five stages of degeneration were classified according to the color, fibrosis, and fragility of the nucleus pulposus of the discs. In order to demonstrate lipofuscin granules, specimens were subjected to special staining procedures, including carbol fuchsin lipofuscin stain, the Schmorl's reaction, and autofluorescence. Lipofuscin granules were distributed from the inner layer of the annulus fibrosus to the nucleus pulposus. Such granules were numerous in cases of slight or severe degeneration, whereas fewer granules were found in cases of moderate degeneration. However, the stage of macroscopic degeneration of the intervertebral disc did not necessarily correlate with the incidence of lipofuscin granules. By ultrastructural observation, the morphological features of the components of the intervertebral disc and the ultrastructure of the lipofuscin granule were clarified. The ultrastructure of the "brown degeneration" disc exhibited markedly increased amorphous electron-dense bodies located among collagen fibrils in the matrix.