Immunohistochemical features of the human retina and retinoblastoma

Temporospatial dynamics of the morphogenesis of the rabbit retina from prenatal to postnatal life: Light and electron microscopic study

The retina consists of various cell types arranged in eight cell layers and two membranes that originate from the neuroectodermal cells. In this study, the timing of differentiation and distribution of the cellular components and the layers of the rabbit retina are investigated using light and electron microscopy and immunohistochemical techniques. There were 32 rabbit embryos and 12 rabbits used. The rabbit retina begins its prenatal development on the 10th day of gestation in the form of optic cup. The process of neuro- and gliogenesis occurs in several stages: In the first stage, the ganglionic cells are differentiated at the 15th day. The second stage includes the differentiation of Muller, amacrine, and cone cells on the 23rd day. The differentiation of bipolar, horizontal, and rod cells and formation of the inner segments of the photoreceptors consider the late stage that occurs by the 27th and 30th day of gestation. On the first week of age postnatally, the outer segments of the photoreceptors are developed. S100 protein is expressed by the Muller cells and its processes that traverse the retina from the outer to the inner limiting membranes. Calretinin is intensely labeled within the amacrine and displaced amacrine cells. Ganglionic cells exhibited moderate immunoreactivity for calretinin confined to their cytoplasm and dendrites. In conclusion, all stages of neuro- and gliogenesis of the rabbit retina occur during the embryonic period. Then, the retina continues its development postnatally by formation of the photoreceptor outer segments and all layers of the retina become established. RESEARCH HIGHLIGHTS: The aim of this study is to investigate the morphogenesis of the rabbit retina during pre- and postnatal life. The primordia of the retina could be observed in the form of the optic cup. The ganglionic cells are the first cells to differentiate, while the photoreceptor cells are the last. S100 protein is expressed by the Muller cells and its processes. Calretinin is intensely labeled in the amacrine and displaced amacrine cells and moderately expressed in the cytoplasm and dendrites of ganglionic cells.

Retinogenesis of the Human Fetal Retina: An Apical Polarity Perspective

The Crumbs complex has prominent roles in the control of apical cell polarity, in the coupling of cell density sensing to downstream cell signaling pathways, and in regulating junctional structures and cell adhesion. The Crumbs complex acts as a conductor orchestrating multiple downstream signaling pathways in epithelial and neuronal tissue development. These pathways lead to the regulation of cell size, cell fate, cell self-renewal, proliferation, differentiation, migration, mitosis, and apoptosis. In retinogenesis, these are all pivotal processes with important roles for the Crumbs complex to maintain proper spatiotemporal cell processes. Loss of Crumbs function in the retina results in loss of the stratified appearance resulting in retinal degeneration and loss of visual function. In this review, we begin by discussing the physiology of vision. We continue by outlining the processes of retinogenesis and how well this is recapitulated between the human fetal retina and human embryonic stem cell (ESC) or induced pluripotent stem cell (iPSC)-derived retinal organoids. Additionally, we discuss the functionality of in utero and preterm human fetal retina and the current level of functionality as detected in human stem cell-derived organoids. We discuss the roles of apical-basal cell polarity in retinogenesis with a focus on Leber congenital amaurosis which leads to blindness shortly after birth. Finally, we discuss Crumbs homolog (CRB)-based gene augmentation.

Immunohistochemical assay for neuron-specific enolase, synaptophysin, and RB-associated protein as a diagnostic aid in advanced retinoblastomas

Purpose

We evaluated the expression of the neural markers, neuron-specific enolase, and synaptophysin, as a tool to confirm the diagnosis of retinoblastoma (RB) in undifferentiated and advanced tumors. Additionally, we determined whether the extent of RB-associated protein (pRb) expression is helpful in assessing the prognosis in RB patients.

Methods

Conventional whole tissue section and tissue microarray immunohistochemistry for neuron-specific enolase, synaptophysin, and pRb were carried out in a series of 22 RBs.

Results

Neuron-specific enolase and synaptophysin were expressed in 75%–100% of the tumor cells, and the staining intensity was strong. Two RBs expressed pRb in 75%–100% of the tumor cells, also with strong staining intensity. Concordance between the immunohistochemical outcomes for whole tissue staining and tissue microarray staining was 76.2% for neuron-specific enolase, 85.7% for synaptophysin, and 80.0% for pRb.

Conclusion

Neuron-specific enolase and synaptophysin have the potential to be useful markers for the diagnosis of RBs. Extensive and strong pRb staining is not associated with less aggressive tumor behavior according to the pathologic classification of RBs.

Identification of differentially expressed proteins in retinoblastoma tumors using mass spectrometry-based comparative proteomic approach

In India, retinoblastoma is among the top five childhood cancers. Children mostly present with extraocular extension and high risk features that results in unsatisfactory treatment and low survival rate. In addition, lack of potential therapeutic and prognostic targets is another challenge in the management of retinoblastoma. We studied comparative proteome of retinoblastoma patients (HPV positive and negative (n=4 each) and controls (n=4), in order to identify potential retinoblastoma-specific protein targets. 2D-DIGE coupled MALDI-TOF/TOF mass spectrometry identified 39 unique proteins. Highly deregulated proteins were GFAP,RBP3,APOA1,CRYAA,CRABP1,SAG and TF. Gene ontology (Panther 7.0) revealed majority of proteins to be associated with metabolic processes (26%) and catalytic activity (38%). 8 proteins were significantly upregulated in HPV positive vis-a-vis HPV negative cases. Patient group exhibited 12 upregulated and 18 downregulated proteins compared to controls. Pathway and network analysis (IPA software) revealed CTNNB1 as most significantly regulated signalling pathway in HPV positive than HPV negative retinoblastoma. The trends in transcriptional change of 9 genes were consistent with those at proteomic level. The Western blot analysis confirmed the expression pattern of RBP3,GFAP and CRABP1. We suggest GFAP,RBP3,CRABP1,CRYAAA,APOA1 and SAG as prospective targets that could further be explored as potential candidates in therapy and may further assist in studying the disease mechanism.

SIGNIFICANCE

In this study we evaluated tumor tissue specimens from retinoblastoma patients and identified 39 differentially regulated proteins compared to healthy retina. From these, we propose RBP3, CRABP1, GFAP, CRYAA, APOA1 and SAG as promising proteomic signatures that could further be explored as efficient prognostic and therapeutic targets in retinoblastoma. The present study is not only a contribution to the ongoing endeavour for the discovery of proteomic signatures in retinoblastoma, but, may also act as a starting point for future studies aimed at uncovering novel targets for further therapeutic interventions and improving patient outcomes.

Recurrent Retinoblastoma With Mandibular Metastasis: A Case Report

Retinoblastoma (RB) is an aggressive intraocular tumor arising from cells of the retina. Infrequently, distant metastasis occurs in advanced stages of the disease. This case report describes the metastasis of the tumor to the mandible, an extremely rare phenomenon. This condition was observed for a recurrent tumor in a patient who initially underwent chemotherapy, making this case report unique and providing new insights into the behavior of this tumor. An overview of the management of a metastatic RB also is discussed.

Immunohistochemistry of apoptosis-related proteins in retinoblastoma

Retinoblastoma is the most common intraocular malignant neoplasia during childhood and results from the partial or total inactivity of the retinoblastoma protein (pRb). In the absence of pRb, the E2F transcription factors increase the levels of cell cycle proteins as well as some pro-apoptotic proteins. We intended to study the immunohistochemistry profile of apoptotic-related proteins in retinoblastoma. We also evaluated the association between the expression of apoptotic protein and stage of tumor or survivor after a 5year follow up. Apoptosis-related proteins (Apaf-1, Bak, Bax, Bcl-2, Bcl-xL, Bim-long, MDM2, p53, pro-caspase-3, PUMA, Smac/DIABLO and cleaved caspase-3) were evaluated using immunohistochemistry on tissue microarrays which contained samples of retinoblastoma tumors taken from ninety-three patients without any treatment previous to surgery. The immunohistochemistry reactions were evaluated using an optical microscope as well as the ACIS III^® platform. The pro-apoptotic proteins (APAF-1, Bax, p53, PUMA, Smac/DIABLO) were more frequently expressed than the anti-apoptotic proteins (Bcl-2, Bcl-xL and MDM2). The protein Bcl-xL had a negative correlation with cleaved caspase-3, a marker of cell apoptosis. Bcl-xL may be implicated in an apoptosis block.

Diffuse anterior retinoblastoma: current concepts

Diffuse anterior retinoblastoma is a rare variant of retinoblastoma seeding in the area of the vitreous base and anterior chamber. Patients with diffuse anterior retinoblastoma are older than those with the classical types, with the mean age being 6.1 years. The original cells of diffuse anterior retinoblastoma are supposed to be cone precursor. Patients most commonly present with pseudouveitis, pseudohypopyon, and increased intraocular pressure. The retina under fundus examination is likely to be normal, and the clinical features mimic the inflammation progress, which can often lead to misdiagnosis. The published diffuse anterior retinoblastoma cases were diagnosed after fine-needle aspiration biopsy running the potential risk of inducing metastasis. The most common treatment for diffuse anterior retinoblastoma is enucleation followed by systematic chemotherapy according to the patient’s presentation and clinical course. This review summarizes the recent advances in etiology (including tumorigenesis and cell origin), pathology, diagnosis, differential diagnosis, and new treatment. The challenges of early diagnosis and prospects are also discussed.

G9a histone methyltransferase activity in retinal progenitors is essential for proper differentiation and survival of mouse retinal cells

In vertebrate retinal development, various transcription factors are known to execute essential activities in gene regulation. Although epigenetic modification is considered to play a pivotal role in retinal development, the exact in vivo role of epigenetic regulation is still poorly understood. We observed that G9a histone methyltransferase, which methylates histone H3 at lysine 9 (H3K9), is substantially expressed in the mouse retina throughout development. To address in vivo G9a function in the mouse retina, we ablated G9a in retinal progenitor cells by conditional gene knock-out (G9a Dkk3 CKO). The G9a Dkk3 CKO retina exhibited severe morphological defects, including photoreceptor rosette formation, a partial loss of the outer nuclear layer, elevated cell death, and persistent cell proliferation. Progenitor cell-related genes, including several cyclins, Hes1, Chx10, and Lhx2, are methylated on histone H3K9 in the wild-type retina, but they were defective in H3K9 methylation and improperly upregulated at late developmental stages in the G9a Dkk3 CKO retina. Notably, conditional depletion of G9a in postmitotic photoreceptor precursors (G9a Crx CKO) led to the development of an almost normal retina, indicating that G9a activity mainly in retinal progenitor cells, but not in photoreceptor precursors, is essential for normal terminal differentiation of and survival of the retina. Our results suggest that proper epigenetic marks in progenitor cells are important for subsequent appropriate terminal differentiation and survival of retinal cells by repressing progenitor cell-related genes in differentiating retinal cells.

Monoallelic but not biallelic loss of Dicer1 promotes tumorigenesis in vivo

Human tumors are characterized by widespread reduction in microRNA (miRNA) expression, although it is unclear how such changes come about and whether they have an etiological role in the disease. Importantly, miRNA knockdown has been shown to enhance the tumorigenic potential of human lung adenocarcinoma cells. A defect in miRNA processing is one possible mechanism for global downregulation. To explore this possibility in more detail in vivo, we have manipulated Dicer1 gene dosage in a mouse model of retinoblastoma. We show that although monoallelic loss of Dicer1 does not affect normal retinal development, it dramatically accelerates tumor formation on a retinoblastoma-sensitized background. Importantly, these tumors retain one wild-type Dicer1 allele and exhibit only a partial decrease in miRNA processing. Accordingly, in silico analysis of human cancer genome data reveals frequent hemizygous, but not homozygous, deletions of DICER1. Strikingly, complete loss of Dicer1 function in mice did not accelerate retinoblastoma formation. miRNA profiling of these tumors identified members of the let-7 and miR-34 families as candidate tumor suppressors in retinoblastoma. We conclude that Dicer1 functions as a haploinsufficient tumor suppressor. This finding has implications for cancer etiology and cancer therapy.

Vimentin isoform expression in the human retina characterized with the monoclonal antibody 3CB2

The antigen recognized by the monoclonal antibody 3CB2 (3CB2-Ag and 3CB2 mAb) is expressed by radial glia and astrocytes in the developing and adult vertebrate central nervous system (CNS) of vertebrates as well as in neural stem cells. Here we identified the 3CB2-Ag as vimentin by proteomic analysis of human glial cell line U-87 extracts (derived from a malignant astrocytoma). Indeed, the 3CB2 mAb recognized three vimentin isoforms in glial cell lines. In the human retina, 3CB2-Ag was expressed in Müller cells, astrocytes, some blood vessels, and cells in the horizontal cell layer, as determined by immunoprecipitation and immunofluorescence. Three populations of astrocytes were distinguishable by double-labeling immunohistochemistry: vimentin+/GFAP+, vimentin-/GFAP+, and vimentin+/GFAP-. Hence, we conclude that 1) the 3CB2-Ag is vimentin; 2) vimentin isoforms are differentially expressed in normal and transformed astrocytes; 3) human retinal astrocytes display molecular heterogeneity; and 4) the 3CB2 mAb is a valuable tool to study vimentin expression and its function in the human retina.

Dicer inactivation leads to progressive functional and structural degeneration of the mouse retina

MicroRNAs (miRNAs) are small, highly conserved molecules that have been shown to regulate the expression of genes by binding to specific target mRNAs. Dicer, an RNase III endonuclease, is essential for the production and function of mature miRNAs, and removal of Dicer has been shown to disrupt many developmental processes. In this study, Dicer was removed specifically from the retina using a floxed Dicer conditional allele and the retinal Chx10Cre transgene. Retinal Dicer knock-out mice displayed a reproducible inability to respond to light. In addition, morphological defects were observed with the formation of photoreceptor rosettes at postnatal day 16, which progressed to more general cellular disorganization and widespread degeneration of retinal cell types as the animals aged. This was accompanied by concomitant decrease in both scotopic and photopic electroretinogram (ERG) responses. Interestingly, removing a single allele of Dicer resulted in ERG deficits throughout life but not to morphological abnormalities. Northern blot analysis of Dicer-depleted retinas showed a decrease in several miRNAs. The observation that progressive retinal degeneration occurred after removal of Dicer raises the possibility that miRNAs are involved in retinal neurodegenerative disorders.

Murine bilateral retinoblastoma exhibiting rapid-onset, metastatic progression and N-myc gene amplification

Human retinoblastoma is a pediatric cancer initiated by RB gene mutations in the developing retina. We have examined the origins and progression of retinoblastoma in mouse models of the disease. Retina-specific inactivation of Rb on a p130-/- genetic background led to bilateral retinoblastoma with rapid kinetics, whereas on a p107-/- background Rb mutation caused predominantly unilateral tumors that arose with delayed kinetics and incomplete penetrance. In both models, retinoblastomas arose from cells at the extreme periphery of the murine retina. Furthermore, late retinoblastomas progressed to invade the brain and metastasized to the cervical lymph nodes. Metastatic tumors lacking Rb and p130 exhibited chromosomal changes revealed by representational oligonucleotide microarray analysis including high-level amplification of the N-myc oncogene. N-myc was found amplified in three of 16 metastatic retinoblastomas lacking Rb and p130 as well as in retinoblastomas lacking Rb and p107. N-myc amplification ranged from 6- to 400-fold and correlated with high N-myc-expression levels. These murine models closely resemble human retinoblastoma in their progression and secondary genetic changes, making them ideal tools for further dissection of steps to tumorigenesis and for testing novel therapies.

Differentiation potential of bone marrow mesenchymal stem cells into retina in normal and laser-injured rat eye

Bone marrow mesenchymal stem cells (MSCs) can develop into hematopoietic and mesenchymal lineages but have not been known to participate in the production of retina. Here we report that bone marrow mesenchymal stem cells, after being subretinally transplanted into normal or Nd: YAG laser-injured rat eye, can integrate into RPE layer, photoreceptor layer, bipolar cell layer and ganglion layer. DAPI-labeling detection was used to trace the origin of the repopulating cells. DAPI fluorescence was used to identify retina cells of bone marrow origin 10, 20, 35 and 50 days after transplantation. No formation of rosettes was found but some random cells were found at the end of the observation. MSCs-originated cells spread more widely in the injured retinas than in the normal ones. Immunohistochemical detection showed that though the cells could express neuronal nuclei (NeuN), neuron specific enolase (NSE), glial fibrillary acidic protein (GFAP) and cytokeratin (CK), the proteins expression in the injured transplantation group was abnormal in some region compared with that in the normal transplantation group. Electroretinogram (ERG) showed that ERG-b wave of the injured transplantation group is significantly higher than that of the two laser-injured control groups. These results suggest that a proportion of MSCs can differentiate into retina-like structure in vivo and the differentiation differs in normal and laser-injured retinas.

Absence of phosphoglucose isomerase-1 in retinal photoreceptor, pigment epithelium and Muller cells

Macroarray analysis was used to compare equal amounts of cDNA from wild-type and rd/rd (retinal degeneration) mice, collected at P90 when photoreceptor degeneration is virtually complete. A stronger signal for the glycolytic enzyme phosphoglucose isomerase (Gpi1) was observed in the rd/rd sample. Extracellularly, Gpi1 may act as a cytokine, independently described as neuroleukin and autocrine motility factor. Retinal Gpi1 expression was investigated by Northern and Western blot analysis and immunohistochemistry. Double-labelling was performed with antibodies against Gpi1 and calbindin-D, glutamine synthetase, RPE65, calretinin and ultraviolet opsin in order to provide positive cell type identification. Northern and Western blots showed double expression levels per microgram of RNA and protein, respectively, in the rd/rd retina compared with wild-type. However, the total amount of Gpi1 protein per retina was indistinguishable. Gpi1 immunoreactivity was found in ganglion, amacrine, horizontal and bipolar cells, but not in rods, cones, pigment epithelium and Muller cells. This distribution explains why the absolute amounts of Gpi1 protein were not appreciably different between wild-type and the rd/rd phenotype, where rods and cones are absent, whilst the relative contribution of Gpi1 to the total protein and RNA pools differed. Some extracellular immunoreactivity was observed in the photoreceptor matrix around cones in freshly fixed tissue only, which could possibly reflect a role as a cytokine. We propose that glycolysis in Gpi1-negative cells proceeds entirely through the pentose phosphate pathway, creating NADPH at the cost of organic carbon. We hypothesize that the unique metabolic needs of photoreceptors justify this trade-off.

Immunohistochemical localization of human pineal tissue antigens in normal retina and retinoblastomas

The normal human retina and retinoblastomas were examined immunohistochemically to assess the localization of pineal antigens in the retina and the oncogenesis and differentiation of retinoblastoma. In the present study, 41 eyes excised from children (aged 4 months to 7 years, all unilateral occurrence) diagnosed to have retinoblastoma and 4 eyes with normal retinas, were used. Retinoblastomas were histopathologically classified into well-differentiated, moderately-differentiated, and poorly-differentiated types. The antibodies used were 9 monoclonal antibodies to human pineal antigens and 6 antibodies to neural tissues. In the normal retina, staining patterns characteristic of retinal cell layers were observed with PP1, PP3, PP5, PP6, PI1, and PI2 antibodies. In retinoblastomas, PP5 antibody, which reacts with horizontal cells and ganglion cells, and PP6 antibody, which reacts with part of the bipolar cells in the inner nuclear layer, showed intense staining in well-differentiated retinoblastomas, but the intensity of staining and the positivity decreased with the degree of dedifferentiation. Antigens recognized by PP3 and PP4 antibodies were positive in all retinoblanstomas. Reactions to GFAP antibody and antibodies that recognize Müller cells were negative. Retinoblanstomas may express markers of not only photoreceptor cells but also other retinal nuclear cells. These results suggest that the retinoblastoma might be developed from visual stem cells, which are common progenitor cells of photoreceptor cells, intermediate neurons, and ganglion cells.

Intermediate-filament expression in ocular tissue

Intermediate-filament proteins (IFPs) occur in the intracellular cytoskeleton of eukaryotic cells, and their expression in diverse tissues is related both to embryology as well as to differentiation. Although the available information concerning their functional properties in vivo is still incomplete, antibodies against individual IFPs are commonly used in immunohistochemical procedures as markers for differentiation, and these antibodies are of outstanding value in the routine histopathological evaluation of tumor specimens. This review presents a compilation of the currently available data concerning IFP expression in normal and diseased ocular tissues. Representatives of every known class of IFP have been detected in normal ocular tissues. The external epithelia exhibit complex expression patterns of cytokeratin (CK) polypeptides, with CK3 and CK12 being specific markers of the corneal epithelium. Recent research has revealed that single mutant CK polypeptides may play a role in the pathogenesis of corneal dystrophies. The internal ocular epithelia reveal simple but specific patterns of IFP expression, these comprising simple-epithelial CKs and/or the mesenchymal IFP, vimentin. The IFP complement of the neuronal structures of the eye embraces several distinct IFP classes and reflects the diversity of the cell types present at these sites. With respect to ocular tumors, the IFP profile of melanomas might be correlated with metastatic potential. In conclusion, IFP analysis may be able to cast light on the pathogenesis of ocular diseases, as well as being a valuable adjunct in ophthalmopathological diagnosis.

Apoptosis in developing retinal tissue

The mechanisms of apoptosis are strongly dependent on cell-cell interactions typical of organized tissues. Experimental studies of apoptosis using a histotypical preparation of retinal explants are reported in the present article. We found that various characteristics of apoptosis are selectively associated with retinal cell death depending on cell type, stage of maturation, and means of induction of apoptosis. Among these were: (1) the requirements of protein synthesis; (2) the role of cAMP; (3) the expression of certain apoptosis-associated proteins; and (4) the sensitivity to excitotoxicity, modulation of protein phosphatases and calcium mobilization. Dividing cells undergo apoptosis in response to several inducers in specific phases of the cell cycle, and in distinct regions within their pathway of interkinetic nuclear migration. Recent post-mitotic cells are selectively sensitive to apoptosis induced by blockade of protein synthesis, while both proliferating and differentiated cells are more resistant. We also studied the association of several proteins, some of which play critical roles in the cell cycle, with both differentiation and apoptosis in the retinal tissue. Detection of cell cycle markers did not support the hypothesis that retinal cells re-enter the cell cycle on their pathway to apoptosis, although some proteins associated with cell proliferation re-appeared in degenerating cells. The transcription factors c-Jun, c-Fos and c-Myc were found associated with apoptosis in retinal cells, but their sub-cellular location in apoptotic bodies is not consistent with their canonical functions in the control of gene expression. The bifunctional redox factor/AP endonuclease Ref-1 and the transcription factor Max are associated with progressive cell differentiation, and both are down-regulated during cell death in the retina. The data suggest that Ref-1 and Max may normally function as negative modulators of retinal apoptosis. The results indicate that nuclear exclusion of transcription factors and other important control proteins is a hallmark of retinal apoptosis. Histotypical explants may be a choice preparation for the experimental analysis of the mechanisms of apoptosis, in the context both of cell-cell interactions and of the dynamic behavior of developing cells within the organized retinal tissue.

Expression patterns of cyclin D1 and related proteins regulating G1-S phase transition in uveal melanoma and retinoblastoma

BACKGROUND/AIMS

A checkpoint mechanism in late G1, whose regulation via loss of retinoblastoma protein (pRB) or p16, or overexpression of cyclin D1 or cyclin dependent kinase 4 (CDK4), has been proposed to constitute a common pathway to malignancy. The aims of this study were (a) to compare markers of cell cycle G1-S phase transition in an intraocular tumour with known pRB deficiency (retinoblastoma) and compare it with one with an apparently functional pRB (uveal melanoma); (b) to determine if one of these markers may have a role in the pathogenesis of uveal melanoma; and (c) to determine if there is a difference in cell cycle marker expression following treatment of uveal melanoma and retinoblastoma.

METHODS

90 eyes were enucleated from 89 patients for retinoblastoma (n = 24) or for choroidal or ciliary body melanoma (n = 66). Conventional paraffin sections were assessed for cell type and degree of differentiation. Additional slides were investigated applying standard immunohistochemical methods with antibodies specific for cyclin D1 protein, pRB, p53, p21, p16, BCL-2, and MIB-1.

RESULTS

Cyclin D1 protein and pRB were negative in retinoblastoma using the applied antibodies. In contrast, cyclin D1 protein expression was observed in 65% of uveal melanomas; a positive correlation between cyclin D1 cell positivity and tumour cell type, location, growth fraction, as well as with pRB positivity was observed. p53, p21, and p16 could be demonstrated in both tumours. An inverse relation between p53 and p21 expression was demonstrated in most choroidal melanomas and in some retinoblastomas. Apart from a decrease in the growth fractions of the tumours as determined by MIB-1, a significant difference in the expression of G1-S phase transition markers in vital areas of uveal melanoma and retinoblastoma following treatment with radiotherapy and/or chemotherapy was not observed.

CONCLUSION

Retinoblastomas and uveal melanomas, two tumours of differing pRB status, differ also in their immunohistochemical pattern for markers of the G1-S phase transition of the cell cycle. The results of the present study support the concept of (a) an autoregulatory loop between pRB and cyclin D1 in tumours with a functional pRB and the disruption of this loop in the presence of pRB mutation, as well as (b) a checkpoint mechanism in late G1, whose regulation via loss of p16 or pRB, or overexpression of cyclin D1 constitutes a common pathway to malignancy. Further, the results raise the possibility of cyclin D1 overexpression having a role in the pathogenesis of uveal melanoma.

Trilateral retinoblastoma: insights into histogenesis and management

Trilateral retinoblastoma (TRb) is a syndrome involving midline intracranial malignancies in children with the heritable form of retinoblastoma. All cases of TRb reported from 1971 to 1997 were reviewed. The histopathologic findings, clinical features, treatment modalities, and survival rates from 80 cases were evaluated. Histopathologic findings from intracranial malignancies demonstrated primitive neuroectodermal tumors in 61.5% of cases. Various degrees of neuronal or photoreceptor differentiation were seen in the other 38.5% of cases. Autopsy, histopathologic, and radiologic examinations did not show a more definitive site of origin of these intracranial tumors, although "pinealoblastoma" was often the diagnosis reported. These findings, together with analysis of the histopathologic similarities among human primitive neuroectodermal tumors, pinealoblastoma, retinoblastoma, and ependymoblastoma, suggest that TRb more likely arises from a germinal layer of predisposed primitive subependymal neuroblasts that are not necessarily destined for pineal or photoreceptor differentiation. Trilateral tumors have also been found in transgenic mice expressing the simian virus 40 T-antigen. Transgenic murine intracranial tumors are primitive neuroectodermal tumors arising from the subependymal layer. Transgenic mice with the murine interphotoreceptor cell binding protein promoter and simian virus 40 T-antigen also develop pineal tumors. Trilateral retinoblastoma is usually fatal, with an average survival time of 11.2 months. Therapies include radiation, systemic chemotherapy, intrathecal chemotherapy, and surgical resection/craniotomy in combination with radiation and/or chemotherapy. Survival may be prolonged with combination chemotherapy (24.6 months) and if neuroradiologic screening identifies TRb before symptoms are present (23.5 months). Recent success with platinum-based chemoreduction of intraocular retinoblastoma may indicate a similar role for platinum-based chemotherapy in the treatment of TRb. Routine central nervous system imaging should be considered in the management of TRb.

AC133, a Novel Marker for Human Hematopoietic Stem and Progenitor Cells

AC133 is one of a new panel of murine hybridoma lines producing monoclonal IgG antibodies (mAbs) to a novel stem cell glycoprotein antigen with a molecular weight of 120 kD. AC133 antigen is selectively expressed on CD34bright hematopoietic stem and progenitor cells (progenitors) derived from human fetal liver and bone marrow, and blood. It is not detectable on other blood cells, cultured human umbilical vein endothelial cells (HUVECs), fibroblast cell lines, or the myeloid leukemia cell line KG1a by standard flow cytometric procedures. All of the noncommitted CD34+ cell population, as well as the majority of CD34+ cells committed to the granulocytic/monocytic pathway, are stained with AC133 antibody. In vitro clonogenicity assays have demonstrated that the CD34+AC133+ double-positive population from adult bone marrow contains the majority of the CFU-GM, a proportion of the CFU-Mix, and a minor population of BFU-E. The CD34dim and AC133− population has been shown to contain the remaining progenitor cells. AC133-selected cells engraft successfully in a fetal sheep transplantation model, and human cells harvested from chimeric fetal sheep bone marrow have been shown to successfully engraft secondary recipients, providing evidence for the long-term repopulating potential of AC133+ cells. A cDNA coding for AC133 antigen has been isolated, which codes for a polypeptide consisting of 865 amino acids (aa) with a predicted size of 97 kD. This antigen is modeled as a 5-transmembrane molecule, a structure that is novel among known cell surface structures. AC133 antibody provides an alternative to CD34 for the selection and characterization of cells necessary for both short- and long-term engraftment, in transplant situations, for studies of ex vivo expansion strategies, and for gene therapy.

AC133, a Novel Marker for Human Hematopoietic Stem and Progenitor Cells

AC133 is one of a new panel of murine hybridoma lines producing monoclonal IgG antibodies (mAbs) to a novel stem cell glycoprotein antigen with a molecular weight of 120 kD. AC133 antigen is selectively expressed on CD34bright hematopoietic stem and progenitor cells (progenitors) derived from human fetal liver and bone marrow, and blood. It is not detectable on other blood cells, cultured human umbilical vein endothelial cells (HUVECs), fibroblast cell lines, or the myeloid leukemia cell line KG1a by standard flow cytometric procedures. All of the noncommitted CD34+ cell population, as well as the majority of CD34+ cells committed to the granulocytic/monocytic pathway, are stained with AC133 antibody. In vitro clonogenicity assays have demonstrated that the CD34+AC133+ double-positive population from adult bone marrow contains the majority of the CFU-GM, a proportion of the CFU-Mix, and a minor population of BFU-E. The CD34dim and AC133− population has been shown to contain the remaining progenitor cells. AC133-selected cells engraft successfully in a fetal sheep transplantation model, and human cells harvested from chimeric fetal sheep bone marrow have been shown to successfully engraft secondary recipients, providing evidence for the long-term repopulating potential of AC133+ cells. A cDNA coding for AC133 antigen has been isolated, which codes for a polypeptide consisting of 865 amino acids (aa) with a predicted size of 97 kD. This antigen is modeled as a 5-transmembrane molecule, a structure that is novel among known cell surface structures. AC133 antibody provides an alternative to CD34 for the selection and characterization of cells necessary for both short- and long-term engraftment, in transplant situations, for studies of ex vivo expansion strategies, and for gene therapy.

Intermediate filaments in the nervous system: implications in cancer

In this review, we describe the different intermediate filament (IF) proteins, their assembly into IFs, the functions of IFs and their relation to disease with a particular emphasis on the intermediate filaments expressed in the nervous system. In the mammalian nervous system, seven intermediate filament proteins are known to be expressed in neurons or neuroblasts. These include the three neurofilament triplet proteins, which are present in both central and peripheral neurons; alpha-internexin, which is the first neuronal intermediate filament protein expressed in the developing mammalian nervous system and present primarily in CNS neurons in the adult nervous system; peripherin, which is most abundant in the PNS; vimentin, which is expressed in neuronal progenitor cells along with nestin, as well as in a few adult neurons. In contrast to these neuron-specific IF proteins, the glial fibrillary acidic protein (GFAP) is glial specific and expressed in mature astrocytes. Vimentin and nestin are also expressed in glial progenitor cells and vimentin is expressed along with GFAP in some mature astrocytes. As a whole, the expression of IF proteins is tissue specific and developmentally regulated. As a result, IF proteins are good markers for determining the cell origin and differentiation status of tumor cells. For example, peripherin is expressed in neuroblastomas, GFAP in astrocytomas and neurofilaments in tumors of neuronal origin. However, tumor cells may express IF patterns which are irrelevant to their cell origin. Therefore, one has to be very careful in using IF patterns as sole indicators of cell origin and differentiation status of tumors.