Biomedical subjects

U Schraermeyer

Publications and source records attributed to U Schraermeyer.

At least 37 records · Page 2Linked to original sources

PubMed1999

Detection of mRNA for proteins involved in retinol metabolism in iris pigment epithelium.

BACKGROUND: To investigate in iris pigment epithelium (IPE) the expression of mRNA for proteins involved in retinol metabolism we used a semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) technique. METHODS: RNA was prepared from freshly isolated bovine IPE and retinal pigment epithelium (RPE) cells and reverse transcribed. The expression of mRNA for cellular retinaldehyde binding protein (CRALBP), p63 (RPE63), the presumed retinal pigment epithelial membrane receptor for retinoids, and 11-cis-dehydrogenase (11cisRDH) was determined by RT-PCR using specific primers. Semi-quantitative expression data were obtained by using a series of fivefold dilution of each cDNA with a fixed number of PCR cycles. RESULTS: Bovine IPE and RPE cells express mRNA for CRALBP, 11cisRDH, and RPE63. The mRNA expression for CRALBP and 11cisRDH is high and equal in both cell types. However, RPE63 mRNA expression in IPE cells is relatively low compared with the expression in RPE cells. CONCLUSIONS: The presence of mRNA for CRALBP, RPE63, and 11cisRDH suggests that IPE cells may be able to metabolize retinol.

Aldehyde Oxidoreductases↗

PubMed1999

Retinal damage by light in the golden hamster: an ultrastructural study in the retinal pigment epithelium and Bruch's membrane.

The mechanism of the toxicity of light on the retina remains unclear despite a large number of investigations. The purpose of this study is to identify and localize the ultrastructural changes and the site of the earliest damage after intense light exposure. Nine adult Syrian golden hamsters (Mesocricetus auratus) have been maintained under constant illumination with a high-pressure mercury lamp (HQJ R 80 W Deluxe, Osram, Berlin, light intensity 1000 lx) for 12 h, followed by an additional 3 h in the dark. Light damage is assessed by light and electron microscopy. Morphological evaluation reveals focal damage to the retinal pigment epithelial (RPE) cells in close proximity to less-affected RPE cells and normal photoreceptors. Collagen fibers in Bruch's membrane lose their parallel orientation. Occasionally, fusion of cell membranes of neighboring rod outer segments (ROS) is also observed. Continuous, 12 h exposure of hamsters to intense light results in initial focal damage to some RPE cells, such that severely damaged RPE cells are found adjacent to intact RPE cells. Only slight damage to the photoreceptors is evident, suggesting that the sequence of the pathological changes resulting from light begins with damage to the RPE cells and associated Bruch's membrane.

Animals↗

PubMed1999

Current understanding on the role of retinal pigment epithelium and its pigmentation.

Retinal pigment epithelium (RPE) is a monolayer of cuboidal cells that is strategically placed between the rod and cone photoreceptors and the vascular bed of the choriocapillaris. It has many important functions, such as phagocytic uptake and breakdown of the shedded photoreceptor membranes, uptake, processing, transport and release of vitamin A (retinol), setting up the ion gradients within the interphotoreceptor matrix, building up the blood-retina barrier, and providing all transport from blood to the retina and back. This short review focuses on the role of the pigment granules in RPE. Although the biology of the pigment granules has been neglected in the past, they do seem to be involved in many important functions, such as protection from oxidative stress, detoxification of peroxides, and binding of zinc and drugs, and, therefore, serve as a versatile partner of the RPE cell. Melanin plays a role in the development of the fovea and routing of optic nerves. New findings show that the melanin granules are connected to the lysosomal degradation pathway. Most of these functions are not yet understood. Deficit of melanin pigment is associated with age-related macula degeneration, the leading cause of blindness.

Age Factors↗

PubMed1999

Rescue effects of IPE transplants in RCS rats: short-term results.

PURPOSE: The aim of this study was to investigate the possible rescue effect of subretinal iris pigment epithelial (IPE) cell transplantation in Royal College of Surgeons (RCS) rats by light and electron microscopic histology. METHODS: IPE cells were harvested from 20- to 26-day-old Long-Evans rats and were directly trans planted transsclerally into the subretinal space of 32 16- to 20-day-old RCS rats using a 32-gauge Hamilton syringe. Specimens of transplanted eyes were embedded for electron microscopy after 8 weeks. Specimens from the iris and retinal pigment epithelium (RPE) of Long-Evans rats and RPE from RCS rats without surgical treatment were also embedded. Sham surgery was also performed in 8 eyes. RESULTS: The IPE cells transplanted into the subretinal space were localized between host RPE and retina, had round cell shapes without polar organization, and contained phagosomes resulting from rod outer segment (ROS) uptake. The underlying host RPE cells were heavily pigmented. RPE cells from RCS rats revealed fragmentation of endoplasmic reticulum, which distinguishes them ultrastructurally from pigment epithelial cells of Long-Evans rats. Ultrastructural alterations were observed in the cytoplasm of transplanted cells. Melanin granules in the IPE cells were found in large vacuoles, which also contained phagosomes originating from ROS uptake. In 13 eyes, 1 to 4 rows and 5 to 8 rows of saved photoreceptors were detected facing transplanted IPE cells in 6 (46%) and 4 (31%) eyes, respectively, 2 months after surgery. However, in 10 (53%) and 7 (37%) of 19 eyes, 1 to 4 rows and 5 to 8 rows, respectively, were also found at sites without IPE cells in the plane of section. ROS directed toward transplanted IPE cells were seen in one case, but these rods were shortened and disorganized. At most sites between transplanted cells and inner segments of photoreceptors, outer segments and cellular debris were absent. In eyes without transplanted cells no photoreceptor cells were alive at the age of 2 months. After sham surgery 6 (75%) eyes had 1 to 4 rows and 2 (25%) 5 to 8 rows of photoreceptors. CONCLUSIONS: Transplanted IPE cells can take up and degrade ROS in vivo in RCS rats. Uptake of ROS alters the morphology of pigment granules in transplanted IPE cells. Pigmentation is an uncertain marker for identifying transplanted pigment cells. IPE transplants are not as good as RPE transplants in rescuing photoreceptors. However, there is a significant difference between transplanted eyes and nontreated eyes. The rescue effect of IPE cells was not significantly different from that of sham surgery.

Animals↗

PubMed1999

Ultrastructural localization of light-induced lipid peroxides in the rat retina.

PURPOSE: Localization of light-induced lipid peroxides in the rat retina at an ultrastructural level as benzidine-reactive substances. METHODS: Long-Evans rats with nondilated pupils were exposed to intense light of 6000 lux for 12 or 24 hours. Control animals were kept under physiological light conditions. Rats with dilated pupils were exposed to a light intensity of 50 lux or 150,000 lux for 1 hour. For ultrastructural localization the enucleated eyes were fixed in a 0.1-M cacodylate buffer (pH 7.4) containing 2% glutaraldehyde for 2 hours. Pieces of the superior part of the central eyecup were incubated overnight with tetramethylbenzidine (TMB; pH 3.0) at 4 degrees C, postfixed with 1.5% OSO4, and embedded for electron microscopy. RESULTS: In animals exposed to intense light, electron-dense structures appeared exclusively throughout the rod outer segments after an irradiation of 6000 lux for 24 hours or 150,000 lux for 1 hour and were absent in animals with nondilated pupils kept at physiological light conditions. Dilation of the pupils leads to the appearance of electron-dense structures after just 1 hour of 50 lux, whereas rats with nondilated pupils withstand even a 12-hour irradiation with 6000 lux. No electron-dense structures were found when no TMB was used in incubation. CONCLUSIONS: The appearance of electron-dense structures in the rod outer segments depends on the incubation with TMB and intensive light exposure of the rat. Dilation of the pupils lowers the threshold for the emergence of electron-dense structures significantly. This strongly supports the view that light-induced lipid peroxides in the rat retina are localized at an ultrastructural level as benzidine-reactive substances. This protocol presents a tool for the generation and ultrastructural localization of lipid peroxides in rat retinas.

Animals↗

PubMed1998

The mRNA expression of cytokines and their receptors in cultured iris pigment epithelial cells: a comparison with retinal pigment epithelial cells.

It has been suggested that human iris pigment epithelial (IPE) cells isolated from iridectomized tissue could be used as autologous cells for transplantation into the subretinal space in diseases with dysfunctional retinal pigment epithelium (RPE). RPE cells synthesize a number of cytokines and their receptors which are important for its proper function. Nearly nothing is known about the capacity of IPE to synthesize cytokines or responding to them. To compare the mRNA expression of 36 cytokines or their receptors in cultured adult IPE cells and RPE cells we used semi-quantitative reverse transcription polymerase chain reactions (RT-PCR). Included in our assay were cytokines with known expression in RPE to get a broad basis for comparing IPE cells: basic fibroblast growth factor (bFGF or FGF-2), and one of its receptor (FGFR-1), epidermal growth factor (EGF), and its receptor EGF-R, transforming growth factor beta(TGFbeta), and its type III receptor TGFbeta-R3, the platelet-derived growth factors and receptors (PDGF A, PDGF B, PDGF-Ralpha, PDGF-Rbeta), tumor necrosis factor alpha(TNFalpha), and two receptors TNF-R1 and TNF-R2, insulin (INS) with receptor INS-R, insulin-like growth factors (IGF1, IGF2), and receptors (IGF1-R, IGF2-R), vascular endothelial growth factor (VEGF), and two receptors (VEGF-R1 or FLT-1 and VEGF-R2 or FLK-1), the receptor for VEGF-C: VEGF-R3 or FLK-4, interleukin 6 (IL6), and its receptor (IL6-R), nerve growth factor (NGF), interleukin 1alpha(IL1alpha), and a receptor (IL1-R). In addition, cytokines or their receptors not known to be expressed in RPE were included to widen our picture of cytokine gene expression in the eye: stem cell factor (SCF), its receptor (SCF-R), low-affinity nerve growth factor receptor p75 (p75(NGF-R), ciliary neutrothropic factor (CNTF), and its receptor (CNTF-R), glycoprotein 130 interleukin 6 transducer (gp130 (IL6-SD), leukemia inhibitory factor (LIF), and its receptor (LIF-R). Semi-quantitative expression data were obtained using series of fivefold dilutions of each cDNA and a fixed number of PCR cycles. The expression of RPE 65, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and beta2-microglobulin (B2MG) was used as a control for cellular origin, RNA quality and PCR conditions. With the exception of insulin and tumor necrosis factor alphaall other cytokines analysed and their receptors were expressed in both IPE and RPE cells, even though the levels varied. No qualitative or quantitative difference were observed in the mRNA expression level of 34 (94%) of the cytokines or receptors between IPE and RPE. In contrast, the mRNA expression level of vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor 2 [VEGF-RS (FLK-1)] was lower in IPE than in RPE cells. As an increased expression of VEGF in the RPE in maculae with age-related macular disease could be involved in its pathogenesis, a decreased expression of angiogenic growth factors in IPE cells could possibly be beneficial for the therapy of age-related maculopathy if indeed other tasks of non-functional RPE cells could be performed by IPE cells. The similarity of the mRNA expression pattern in 94% of the cytokines analyzed supports the assumption that IPE cells potentially can perform functions of RPE cells in the appropriate environment.

Adult↗

PubMed1998

The nonradioisotopic representation of differentially expressed mRNA by a combination of RNA fingerprinting and differential display.

In many applications, an understanding of differentially expressed genes in different tissues or owing to an applied stimulus is important. However, the wide use of two rather similar polymerase chain reaction (PCR)-based techniques for the identification of differentially expressed mRNAs (RNA fingerprinting by arbitrarily primed PCR [RAP-PCR] and differential display [DDRT-PCR]) has shown that reproducibility is still a problem. By combining features of both RAP-PCR and DDRT-PCR, a technique has recently been developed that avoids some of the disadvantages, but the use of radioisotopes for band detection still limits its application. We have improved this technique for analyzing differentially expressed mRNA by resolving the amplified products on nondenaturing polyacrylamide gels and subsequently staining the gels with silver nitrate. Our modification allows the identification of differentially expressed bands with a very high accuracy. Therefore these bands can be very easily reamplified and sequenced directly. Subsequently the differential expression can be verified by semiquantitative RT-PCR with specific primers derived from sequence data. These improvements, together with nonradioactive sequencing techniques, make it possible to do DD analysis completely without a health hazardous owing to radioactivity. The nonradioisotopic differentially expressed mRNA-PCR (DEmRNA-PCR) is a reliable and useful modification of available differential expression methods.

Cells, Cultured↗

PubMed1998

[Ultrastructural localization of lipid peroxides in the eye. Presentation of a new method].

UNLABELLED: Lipid peroxidation is considered a prominent feature of age-related retinal degeneration. It is known that lipid peroxides can oxidize benzidine. This property was used to localize lipid peroxides ultrastructurally in the retina. METHODS: (1) Lipid peroxides were formed by incubation of linoleic acid with lipoxygenase from soybean, separated by thin layer chromatography and incubated with tetramethylbenzidine. (2) Lipid peroxides were formed by incubation of porcine retinae with soybean lipoxygenase in an oxygensaturated atmosphere. For ultrastructural localization, isolated retinae with and without enzymatically synthesized lipid peroxides were fixed with 2% glutaraldehyde, incubated with 0.5 mg/ml tetramethylbenzidine and embedded for electron microscopy. (3) Eye cups from Syrian golden hamsters were treated in the same way except for incubation with lipoxygenase. The hamsters were kept under constant illumination (1000 lux) for 12 h to enhance lipid peroxidation. RESULTS: (1) Tetramethylbenzidine was oxidized by linoleic acid peroxides. (2) In the isolated retinae of pigs lipid peroxides became visible as electron-dense structures in the rod outer segments (ROS) after treatment with lipoxygenase and were lacking in the other parts of the retina. Without treatment with lipoxygenase lipid peroxides were only infrequently seen in ROS. (3) In the eyes of light-exposed hamsters, electron-dense reaction products of lipid peroxides were particularly prominent between the basal infoldings of the RPE and within the apical parts of the ROS. CONCLUSION: Light or enzymatically induced lipid peroxides can be localized ultrastructurally due to their ability to react with tetramethylbenzidine and osmium in the absence of H2O2 to an electron-dense reaction product. Lipid peroxides seem to be removed from the RPE via Bruch's membrane and blood vessels. Disturbance of this pathway may enhance lipofuscin or drusen formation.

Animals↗

PubMed1998

Phagocytosis of rod outer segments by human iris pigment epithelial cells in vitro.

BACKGROUND: We set out to evaluate the growth potential of human iris pigment epithelial (hIPE) cells in vitro, to establish whether these cells acquire the ability to phagocytose rod outer segments (ROS) and to compare the phagocytic activity of hIPE to that of human retinal pigment epithelial (hRPE) cells. METHODS: hIPE and hRPE cells were isolated and cultured from human donor eyes and surgical specimens and growth characteristics were analyzed. HIPE and hRPE of an eye of a 46-year-old donor were used for the phagocytosis assay. Phagocytosis was evaluated by adding ROS isolated from porcine retina to cultures of hIPE and hRPE, which had been labeled with the pH-sensitive fluorescent dye, carboxy-SNAFL. After 4 h the number of ingested ROS was counted with a light microscope. For each cell type phagosomes in 500 cells were counted. The epithelial characteristics of the cells used in this study were evidenced by their morphology. RESULTS: Morphologically cultured hIPE are indistinguishable from the hRPE cultured from the same donor eye and show a similar pattern of cytokeratin distribution. Cultured hIPE acquire the ability to phagocytose ROS at a level slightly lower than hRPE; hIPE contained 0.76 phagosomes per cell, hRPE 0.99 phagosomes per cell. CONCLUSION: The morphology of hIPE in culture and the acquisition of the phagocytic phenotype indicate that these cells have the ability to differentiate into cells that have characteristics in common with hRPE. The acquisition of phagocytic activity suggests that it is feasible to culture hIPE from surgical iridectomies and that these cultured cells can be transplanted into the subretinal space in individuals with retinal degenerations.

Cells, Cultured↗

PubMed1998

Capillaries are present in Bruch's membrane at the ora serrata in the human eye.

PURPOSE: Because earlier studies indicate that the choroid close to the ora serrata may have unique anatomic features such as wandering cells, blood vessels in Bruch's membrane, and accumulated pigment in the retinal pigment epithelium (RPE), the morphology of the normal human eye at the ora serrata region was investigated. METHODS: Specimens from the ora serrata region of two normal human eyes (male donors, 48 and 52 years old) were investigated by light and electron microscope. Specimens from all quadrants were studied in one eye. RESULTS: The elastic layer of Bruch's membrane extended as far as 15 microm into the peripheral choroid; capillaries were included between the elastin layer and the RPE. Nasally, from the anterior end to 2 mm posterior of the ora serrata, the RPE cells contained more melanin than did those in the adjacent posterior region. Melanin granules in the RPE cells close to the ora either formed large clusters or appeared unusually small because of fragmentation. A unique, fine lamellar, membranous material with a fingerprint-like structure was found between the basal folds of the RPE. This material is also found within the extracellular matrix of the choroid and in association with red blood cells. CONCLUSIONS: The morphology of Bruch's membrane is varied near the ora serrata because capillaries and wandering cells are present in its outer collagenous layer. Unique, fine lamellar, fingerprint-like structures are extruded from the RPE and are removed from the eye together with red blood cells. Capillaries within the inner collagenous region of Bruch's membrane at the ora serrata may not necessarily represent a pathologic response but may be a normal characteristic of thick regions of Bruch's membrane.

Bruch Membrane↗

PubMed1997

Porcine iris pigment epithelial cells can take up retinal outer segments.

This study investigates the ability of iris epithelial cells (IPE) to ingest rod outer segments (ROS) and compares the amount of phagocytosis of porcine RPE and IPE cells by the use of a pH sensitive fluorescent dye (carboxy SNAFL) at the light microscopic level. The dye allowed investigation of ingestion separately from binding of rod outer segments. In a second set of experiments, after exposing ferritin-labeled ROS to the cultured cells, phagosomes were also counted in electron microscopic sections. Additionally immunocytochemical staining was performed with IPE and RPE cells. Both cell types stained positive with polyclonal NaK-ATPase antibodies against the alpha 1 subunit from rat brain and kidney. The epithelial nature of the cultured cells was determined by monoclonal anti-human-cytokeratin antibodies. Moreover, the ultrastructure of the cells revealed high amounts of phagosomes smaller than 1 micron in diameter present in both RPE and IPE cells. The iron label of the phagosomes was determined by EELS spectra taken from individual phagosomes. Electron and light microscopic quantification shows that cultured IPE cells have 64% of the phagocytic capacity of the RPE with respect to phagosomes larger than 1 micron in diameter.

Animals↗

PubMed1997

Apoptosis in proliferative vitreoretinal disorders: possible involvement of TGF-beta-induced RPE cell apoptosis.

The targeted induction of apoptosis is a novel therapeutic approach to control the unlimited growth of proliferating cells. Since massive proliferation of cells at the vitreoretinal interface is a key feature of proliferative vitreoretinal disorders, we sought to identify apoptosis in epiretinal membranes from patients with proliferative vitreoretinopathy (PVR), proliferative diabetic retinopathy (PDR) and macular pucker. Further, we evaluated the possible induction of apoptosis of retinal pigment epithelial (RPE) cells by transforming growth factor-beta(TGF-beta). Apoptotic cells were identified by in situ DNA end labeling and acridine orange staining on paraffin-embedded tissue sections from epiretinal membranes of patients with all vitreoretinal disorders examined. Labeled nuclei or condensed chromatin were scattered throughout the membranes or occurred in clusters. Most apoptotic cells were RPE-derived, as assessed by cytokeratin immunochemistry. No apoptotic glial cells were detected. In PVR, proliferative activity, as confirmed by Ki-67 immunochemistry, was associated with short history and rapid disease progression. Apoptotic nuclei were observed more frequently in long-standing PVR or slow progression towards traction retinal detachment. TGF-beta was detected in all control vitreous samples by bioassay at concentrations below 20 ng ml-1. TGF-beta levels increased up to 20-fold in pathological vitreous. Marked heterogeneity was observed in all patient groups. The degree of TGF-beta activation was significantly higher in PVR than in PDR. Proapoptotic effects of TGF-beta were demonstrated in cultured human RPE cells by electron microscopy, in situ DNA end labeling, comet assay and a photometric enzyme immunoassay for histone-associated DNA fragments. Apoptosis appears to be a key regulatory mechanism of growth control of specific cell populations in proliferative vitreoretinal disorders. Administration of proapoptotic growth factors such as TGF-beta may provide a novel approach to inhibit cellular proliferation at the vitreoretinal interface.

Apoptosis↗

PubMed1997

Cytochemical localization of guanylate cyclase in photoreceptor cells of the mouse.

BACKGROUND: Light-stimulated excitation causes a decrease of the cGMP concentration in vertebrate photoreceptor cells. The cGMP content is restored by the catalytic action of a guanylate cyclase (EC 4.6.1.2). METHODS: The spatial distribution of guanylate cyclase was determined cytochemically in rod visual cells of the mouse. RESULTS: In retinal tissue of the mouse guanylate cyclase was found throughout the photoreceptor cells, in the outer and the inner segments, and was especially prominent in the cilia and in elongations of cilia extending into the outer segments. A reaction product of adenylate cyclase (EC 4.6.1.1) could not be demonstrated in vertebrate rod outer segments. CONCLUSION: The relatively high amount of guanylate cyclase in the inner segments and the cilia may contribute-at least in part-to the actual concentration and the time course of concentration changes of the cGMP concentration in rod outer segments.

Adenylyl Imidodiphosphate↗

PubMed1997

Retinal pigment epithelial cells: autocrine and paracrine stimulation of extracellular matrix contraction.

BACKGROUND: This study was carried out to examine the biological activity of contraction promoters produced by dedifferentiating retinal pigment epithelial cells (RPE) and to evaluate the importance of autocrine and paracrine effects within a semi-closed environment like the vitreal cavity. METHODS: RPE at different stages of dedifferentiation in culture were examined for their ability (a) to generate tractional forces in vitro, with and without serum stimulation, and (b) to produce and release contraction-stimulating proteins. Autocrine versus paracrine effects of cell-secreted promoters were tested by using RPE or human dermal fibroblasts (HDF) as target cells. The contraction-stimulating activity of the cell-secreted promoters was partially characterized and compared to the activity of defined promoters. RESULTS: Our study confirmed that RPE can synthesize and secrete cell-contraction-promoting factor(s) active in stimulating the development of tractional forces by RPE as well as HDF. The quantity of biological activity secreted per cell decreases with progressive dedifferentiation, yet the responsiveness of the cell to contraction promoters increases. The contraction promoter(s) synthesized by RPE is partially distinct from the promoters in serum, TGF-beta 1 and beta 2, IGF-1, ET-1 and PDGF. The contraction-promoting effects of the RPE product(s) can be completely blocked by staurosporine. CONCLUSION: De-differentiation of RPE is characterized by increasing capacity to generate tractional forces and decreasing synthetic capacity. RPE within a semi-closed system like the vitreal cavity can, theoretically, act both as promoting and active component of traction-related events (tractional retinal detachment).

Animals↗

PubMed1997

Descemet's membrane as membranous support in RPE/IPE transplantation.

PURPOSE: The correct orientation of retinal pigment epithelium (RPE) cells is necessary for the integrity and proper function of the retina. For transplantation of RPE/iris pigment epithelium (IPE) grafts to the subretinal space in age-related macular degeneration, this cellular orientation is most effectively provided by a membranous support. The goal of this study was to establish an autologous or homologous membrane as a substratum for the growth of RPE/IPE. METHODS: Porcine and bovine RPE and IPE were placed in primary culture on a dissected sheet (5 x 5 mm) of autologous porcine and bovine Descemet's membrane in slide chambers and grown to confluence. RESULTS: RPE and IPE cells cultured on Descemet's membrane form an intact monolayer. Light and electron microscopy showed the formation of both an intact monolayer and microvilli in both cell types. CONCLUSION: Since the slow host-graft rejection appears to play an important role in the failure of RPE transplantation in the subretinal space, it is critical to be able to transplant autologous materials. The techniques presented here establish a novel means to culture RPE or IPE cells on autologous Descemet's membrane where they form a "cell monolayer patch," consisting of a fragment of Descemet's membrane with cultured RPE or IPE, which can be easily manipulated and transplanted, using an established glass pipette method.

Animals↗

PubMed1996

Detection of a fine lamellar gridwork after degradation of ocular melanin granules by cultured peritoneal macrophages.

In the present study we investigated by electron microscopy whether melanin granules derived from choroidal melanocytes and retinal pigment epithelium of cattle could be degraded in the phagolysosomes of cultured murine macrophages. It was found that degradation of ocular melanin is possible by the lysosomes of these macrophages. During degradation of the melanin granules an internal gridwork of fine concentric, highly ordered membranes, 3-4 nm thick, became visible. These membranes may represent remnants of the melanin polymer in the original melanosome or may result from self-assembly of degradation products. Early-stage melanosome-like structures also appeared during digestion of these melanin granules. Melanin granules that seemed to break down into smaller fragments without any visible internal structure were also observed.

Animals↗

PubMed1996

Heterogeneous ultrastructure of melanosome formation in the goldfish induced by osmotic stress.

In this study, melanophore cytodifferentiation in the fins of xanthic goldfish that had been exposed to osmotic stress for 18 days was investigated. It was found that multi-vesicular bodies (MVB) are not the only type of premelanosome. Granules having a homogeneous matrix also function as premelanosomes. The presence of acid phosphatase reaction product inside the melanin granules indicated that these organelles in this animal were also related to lysosomes. DOPA-oxidase of tyrosinase, the key enzyme in melanogenesis, was surprisingly not only detected in melanocytes but also in the Golgi stacks of dermal cells. Due to the mechanisms of premelanosome formation it is evident that cytoplasmic material also serves as substrate for melanogenesis. EDX microanalysis was performed to measure the ionic composition of the melanin granules. After aldehyde fixation the newly-formed melanin granules did not contain Na, but had accumulated Ca.

Acid Phosphatase↗

PubMed1996

The intracellular origin of the melanosome in pigment cells: a review of ultrastructural data.

This paper is a review about the ultrastructural data dealing with the origin of the melanin granules in retinal pigment epithelial cells, in melanocytes, in the ink gland of cuttle fish, in Kupffer cells of the liver, in neuronal tissues, in cultured pigment cells. The role and structure of lysosomes in melanogenesis are discussed in a separate chapter. The early steps of melanogenesis are ultrastructurally very heterogeneous, even in the same cell types. With respect to this heterogeneity and the considerably different views on melanosome origin in the literature, the author hypothesizes that pigment cells may use protein matrices originated from different cellular pathways. 1) They may either produce a specific protein matrix and be converted into melanin in the classical way, or 2) alternatively, a matrix resulting from lysosomal protein degradation or endocytotic pathways may be used and converted into melanin, as found in fibroblasts transfected with the tyrosinase gen or in Kupffer cells. The very heterogeneous ultrastructure of the polymerizing melanin may be influenced by the amount and sterical availability of tyrosine residues in the protein moieties and the activity of tyrosinase.

Animals↗