RESUMEN
During ocular development, periocular neural crest cells (pNC) migrate into the region between the lens and presumptive corneal epithelium to form the corneal endothelium and stromal keratocytes. Although defects in neural crest cell development are associated with ocular dysgenesis, very little is known about the molecular mechanisms involved in this process. This study focuses on the corneal endothelium, a monolayer of specialized cells that are essential for maintaining normal hydration and transparency of the cornea. In avians, corneal endothelial cells are first to be specified from the pNC during their migration into the presumptive corneal region. To investigate the signals required for formation of the corneal endothelium, we utilized orthotopic and heterotopic injections of dissociated quail pNC into chick ocular regions. We find that pNC are multipotent and that the nascent cornea is competent to induce differentiation of ectopically injected pNC into corneal endothelium. Injected pNC downregulate expression of multipotency transcription factors and upregulate genes that are consistent with ontogenesis of the chick corneal endothelium. Importantly, we showed that TGFß2 is expressed by the nascent lens and the corneal endothelium, and that TGFß signaling plays a critical role in changing the molecular signature of pNC in vitro. Collectively, our results demonstrate the significance of the ocular environmental cues towards pNC differentiation, and have potential implications for clinical application of stem cells in the anterior segment.
Asunto(s)
Proteínas Aviares/metabolismo , Endotelio Corneal/embriología , Cresta Neural/embriología , Transducción de Señal/fisiología , Factor de Crecimiento Transformador beta2/metabolismo , Animales , Embrión de Pollo , Pollos , Endotelio Corneal/citología , Cresta Neural/citologíaRESUMEN
Purpose: To investigate the initial events in the development of the human cornea, focusing on cell migration, and extracellular matrix synthesis and organization. To determine whether elastic fibers are present in the extracellular matrix during early human corneal development. Methods: Human corneas were collected from week 7 to week 17 of development. An elastic fiber-enhancing stain, tannic acid-uranyl acetate, was applied to all tissue. Three-dimensional serial block-face scanning electron microscopy combined with conventional transmission electron microscopy was used to analyze the corneal stroma. Results: An acellular collagenous primary stroma with an orthogonal arrangement of fibrils was identified in the central cornea from week 7 of corneal development. At week 7.5, mesenchymal cells migrated toward the central cornea and associated with the acellular collagenous matrix. Novel cell extensions from the endothelium were identified. Elastic fibers were found concentrated in the posterior peripheral corneal stroma from week 12 of corneal development. Conclusions: This study provides novel evidence of an acellular primary stroma in the early development of the embryonic human cornea. Cell extensions exist as part of a communication system and are hypothesized to assist in the migration of the mesenchymal cells and the development of the mature cornea. Elastic fibers identified in early corneal development may play an important role in establishing corneal shape.
Asunto(s)
Córnea/embriología , Sustancia Propia/embriología , Tejido Elástico/embriología , Endotelio Corneal/embriología , Movimiento Celular/fisiología , Córnea/ultraestructura , Sustancia Propia/ultraestructura , Tejido Elástico/ultraestructura , Endotelio Corneal/ultraestructura , Matriz Extracelular/ultraestructura , Edad Gestacional , Humanos , Imagenología Tridimensional , Microscopía Electrónica de Rastreo , Microscopía Electrónica de TransmisiónRESUMEN
PURPOSE: The homeodomain transcription factor, PITX2, is at the apex of a genetic pathway required for corneal development, but the critical effector genes regulated by the PITX2 remain unknown. The purpose of this study was to discover and validate PITX2-dependent mechanisms required for specifying cell lineages and establishing angiogenic privilege within the developing cornea. METHODS: Microarrays were used to compare gene expression in corneas isolated from temporal Pitx2 knockout embryos and control littermates. Quantitative RT-PCR and immunohistochemistry was used to further validate Tfap2b expression differences in Pitx2 knockout versus control corneas. In situ hybridization and protein immunohistochemistry were used to assay eyes of a Tfap2b allelic series of embryos to identify differentiated cellular lineages in the cornea, blood vessel endothelium, or lymphatic vessel endothelium. RESULTS: We show that PITX2 is required for the expression of Tfap2b, encoding the AP-2ß transcription factor, in the neural crest during corneal development. Markers of differentiated corneal epithelium and stroma are expressed in the absence of AP-2ß. In contrast, markers of differentiated corneal endothelium are not expressed in the absence of AP-2ß. Endomucin+ blood vessels are present throughout the developing corneal stroma in the absence of AP-2ß, whereas LYVE1+ lymphatic vessels are not found. CONCLUSIONS: The AP-2ß transcription factor is an important effector of PITX2 function during corneal development, required for differentiation of corneal endothelium and establishment of angiogenic privilege. Unlike PITX2, AP-2ß is not required for the early expression of available lineage specific markers for the corneal epithelium and stroma during embryogenesis, nor establishment of lymphangiogenic privilege. Therefore, additional PITX2-dependent factors likely regulate these latter processes during embryonic development. These results extend our understanding of the genetic mechanisms regulating cornea development.
Asunto(s)
Endotelio Corneal/embriología , Regulación del Desarrollo de la Expresión Génica , Proteínas de Homeodominio/genética , Morfogénesis/genética , Neovascularización Fisiológica/genética , Preñez , Factor de Transcripción AP-2/genética , Factores de Transcripción/genética , Animales , Diferenciación Celular , Córnea/embriología , Córnea/metabolismo , Endotelio Corneal/metabolismo , Femenino , Proteínas de Homeodominio/biosíntesis , Proteínas de Homeodominio/metabolismo , Inmunohistoquímica , Hibridación in Situ , Ratones , Ratones Noqueados , Embarazo , Factor de Transcripción AP-2/metabolismo , Factores de Transcripción/biosíntesis , Factores de Transcripción/metabolismo , Proteína del Homeodomínio PITX2RESUMEN
Development of the vertebrate cornea is a multistep process that involves cellular interactions between various ectodermal-derived tissues. Bilateral interactions between the neural ectoderm-derived optic vesicles and the cranial ectoderm give rise to the presumptive corneal epithelium and other epithelia of the ocular surface. Interactions between the neural tube and the adjacent ectoderm give rise to the neural crest cells, a highly migratory and multipotent cell population. Neural crest cells migrate between the lens and presumptive corneal epithelium to form the corneal endothelium and the stromal keratocytes. The sensory nerves that abundantly innervate the corneal stroma and epithelium originate from the neural crest- and ectodermal placode-derived trigeminal ganglion. Concomitant with corneal innervation is the formation of the limbal vascular plexus and the establishment of corneal avascularity. This review summarizes historical and current research to provide an overview of the genesis of the cellular layers of the cornea, corneal innervation, and avascularity.
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Córnea/citología , Córnea/embriología , Células Madre/citología , Animales , Córnea/irrigación sanguínea , Córnea/inervación , Sustancia Propia/citología , Sustancia Propia/embriología , Desarrollo Embrionario , Endotelio Corneal/citología , Endotelio Corneal/embriología , Epitelio Corneal/citología , Epitelio Corneal/embriología , HumanosRESUMEN
The human cornea contains stem cells that can be induced to express markers consistent with multipotency in cell culture; however, there have been no studies demonstrating that human corneal keratocytes are multipotent. The objective of this study is to examine the potential of human fetal keratocytes (HFKs) to differentiate into neural crest-derived tissues when challenged in an embryonic environment. HFKs were injected bilaterally into the cranial mesenchyme adjacent to the neural tube and the periocular mesenchyme in chick embryos at embryonic days 1.5 and 3, respectively. The injected keratocytes were detected by immunofluorescence using the human cell-specific marker, HuNu. HuNu-positive keratocytes injected along the neural crest pathway were localized adjacent to HNK-1-positive migratory host neural crest cells and in the cardiac cushion mesenchyme. The HuNu-positive cells transformed into neural crest derivatives such as smooth muscle in cranial blood vessels, stromal keratocytes, and corneal endothelium. However, they failed to form neurons despite their presence in the condensing trigeminal ganglion. These results show that HFKs retain the ability to differentiate into some neural crest-derived tissues. Their ability to respond to embryonic cues and generate corneal endothelium and stromal keratocytes provides a basis for understanding the feasibility of creating specialized cells for possible use in regenerative medicine.
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Diferenciación Celular , Queratocitos de la Córnea/fisiología , Endotelio Corneal/citología , Animales , Movimiento Celular , Células Cultivadas , Embrión de Pollo , Córnea/citología , Córnea/embriología , Queratocitos de la Córnea/trasplante , Vasos Coronarios/citología , Endotelio Corneal/embriología , Feto/citología , Humanos , Microinyecciones , Cresta Neural/citología , Cráneo/irrigación sanguínea , Ganglio del Trigémino/citologíaRESUMEN
During embryonic development, surface ectoderm differentiates to form corneal, conjunctival, and eyelid epidermal epithelia, and glandular epithelium (lacrimal and meibomian glands). Periocular mesenchymal cells of neural crest origin migrate and differentiate, leading to the formation of corneal endothelium and the stromas of the cornea, conjunctiva, eyelids, and trabecular meshwork. The formation of functional ocular surface tissues requires coordinated spatial and temporal expression of transcription factors and signaling molecules of various cytokines and signaling pathways, and the synthesis and remodeling of unique extracellular matrix. Although bidirectional interactions and signaling between mesenchyme and epithelium are considered necessary for embryonic formation of ocular surface tissues and homeostasis in adults, the molecular and cellular mechanisms that regulate such processes remain largely unknown. To investigate possible mechanisms, we have developed mouse models in which the gene functions of ocular surface epithelia and stromas can be altered by Doxycycline induction in spatial and temporal specific manners.
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Conjuntiva/embriología , Sustancia Propia/embriología , Endotelio Corneal/embriología , Transición Epitelial-Mesenquimal/fisiología , Epitelio Corneal/embriología , Regulación del Desarrollo de la Expresión Génica/fisiología , Morfogénesis/fisiología , Animales , HumanosRESUMEN
Primary cilia are required for several signaling pathways, but their function in cellular morphogenesis is poorly understood. Here we show that emergence of an hexagonal cellular pattern during development of the corneal endothelium (CE), a monolayer of neural crest-derived cells that maintains corneal transparency, depends on a precise temporal control of assembly of primary cilia that subsequently disassemble in adult corneal endothelial cells (CECs). However, cilia reassembly occurs rapidly in response to an in vivo mechanical injury and precedes basal body polarization and cellular elongation in mature CECs neighboring the wound. In contrast, CE from hypomorphic IFT88 mutants (Tg737(orpk)) or following in vivo lentiviral-mediated IFT88 knockdown display dysfunctional cilia and show disorganized patterning, mislocalization of junctional markers, and accumulation of cytoplasmic acetylated tubulin. Our results indicate an active role of cilia in orchestrating coordinated morphogenesis of CECs during development and repair and define the murine CE as a powerful in vivo system to study ciliary-based cellular dynamics.
Asunto(s)
Cilios/fisiología , Pérdida de Celulas Endoteliales de la Córnea/fisiopatología , Endotelio Corneal/embriología , Endotelio Corneal/lesiones , Morfogénesis , Animales , Endotelio Corneal/ultraestructura , Técnicas de Silenciamiento del Gen , Etiquetado Corte-Fin in Situ , Ratones , Ratones Endogámicos C57BL , Microscopía Electrónica de Rastreo , Microscopía Fluorescente , Interferencia de ARN , Proteínas Supresoras de Tumor/genéticaRESUMEN
PURPOSE: The zinc finger transcription factor Zeb1 binds to E-box-like sequences and is important for maintaining repression of epithelial specification genes in vivo. Overexpression of Zeb1 in cancer triggers epithelial-mesenchymal transition, which facilitates metastasis. The mutation of ZEB1 in humans is linked to posterior polymorphous corneal dystrophy (PPCD), in which an epithelial transition of the corneal endothelium is associated with abnormal endothelial proliferation. The purpose of this study is to determine whether Zeb1 null or heterozygous mice may provide an animal model for PPCD. METHODS: Corneal morphology, protein and mRNA expression, and cell proliferation were compared in wild-type and Zeb1 gene knockout mice by immunostaining, real-time PCR, and BrdU incorporation. mRNA expression in isolated embryo fibroblasts derived from wild-type, Zeb1 heterozygous, and null mice was analyzed by real-time PCR RESULTS: Zeb1 null mice late in gestation show ectopic expression of epithelial genes in the corneal endothelium and keratocytes, including the basement membrane component COL4A3, which is ectopically expressed by the corneal endothelium in PPCD. These embryos also show abnormal corneal endothelial and keratocyte proliferation, corneal thickening, and corneolenticular and iridocorneal adhesions. Adult Zeb1 heterozygous mice exhibit these same corneal defects. The ectopic expression of epithelial genes extended to embryonic fibroblasts derived from Zeb1 heterozygous and null mice, suggesting that Zeb1 may have a more general role in the suppression of an epithelial phenotype. CONCLUSIONS: The authors conclude that Zeb1 heterozygous and null mice show features of PPCD and thus should provide an animal model for genetic dissection of pathways contributing to the disease.
Asunto(s)
Distrofias Hereditarias de la Córnea/genética , Modelos Animales de Enfermedad , Endotelio Corneal/metabolismo , Proteínas de Homeodominio/fisiología , Factores de Transcripción de Tipo Kruppel/fisiología , Mutación/fisiología , Dedos de Zinc/fisiología , Animales , Autoantígenos/genética , Autoantígenos/metabolismo , Bromodesoxiuridina/metabolismo , Cadherinas/genética , Cadherinas/metabolismo , Proliferación Celular , Colágeno Tipo IV/genética , Colágeno Tipo IV/metabolismo , Distrofias Hereditarias de la Córnea/embriología , Distrofias Hereditarias de la Córnea/patología , Endotelio Corneal/embriología , Endotelio Corneal/patología , Epitelio Corneal/embriología , Epitelio Corneal/metabolismo , Epitelio Corneal/patología , Femenino , Fibroblastos/metabolismo , Técnica del Anticuerpo Fluorescente Indirecta , Dosificación de Gen , Genotipo , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , ARN Mensajero/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Homeobox 1 de Unión a la E-Box con Dedos de ZincRESUMEN
PURPOSE: Collagen fibrils and proteoglycans are the main components of the corneal extracellular matrix and corneal transparency depends crucially on their proper arrangement. In the present study, we investigated the formation of collagen fibrils and proteoglycans in the developing cornea of the zebrafish, a model organism used to study vertebrate embryonic development and genetic disease. METHODS: We employed thin-section electron microscopy to investigate the ultrastructure of the zebrafish cornea at different developmental stages. RESULTS: The layering of the zebrafish cornea into an epithelium, a Bowman's layer, stroma and endothelium was observed starting at 72 hr post-fertilization. At this stage, the stroma contained orthogonally arranged collagen fibrils and small proteoglycans. The density of proteoglycans increased gradually throughout subsequent development of the cornea. In the stroma of 2-week-old larvae, the collagen fibrils were organized into thin lamellae and were separated by very large, randomly distributed proteoglycans. At 4 weeks, a regular arrangement of proteoglycans in relation to the collagen fibrils was observed for the first time and the lamellae were also thickened. CONCLUSION: The present study, for the first time, provides ultrastructural details of collagen fibril and proteoglycan development in the zebrafish cornea. Furthermore, it directly correlates the collagen fibril and proteoglycan composition of the zebrafish cornea with that of the human cornea. The similarities between the two species suggest that the zebrafish could serve as a model for investigating the genetics of human corneal development and diseases.
Asunto(s)
Sustancia Propia/embriología , Colágenos Fibrilares/ultraestructura , Proteoglicanos/ultraestructura , Pez Cebra/embriología , Anciano , Animales , Sustancia Propia/ultraestructura , Desarrollo Embrionario , Endotelio Corneal/embriología , Endotelio Corneal/ultraestructura , Humanos , Microscopía Electrónica de Transmisión , MorfogénesisRESUMEN
PURPOSE: To examine the expression of transcription factor Sp1 in the cornea of the mouse eye throughout developmental stages. The environmental effect of light on Sp1 expression was also assessed. METHODS: C57BL/6 mice were set up for timed mating. Embryos on embryonic day (E)10.5, E12.5, E15.5, and E18.5 and eyes from mice on postnatal day (P)0, P7, P11, P15, P30, and P60 were collected for immunohistochemical staining and in situ hybridization. One group of mice was bred strictly in the dark between E18.5 and P15, and the eyes were collected at P0, P7, P11, and P15 time points. RESULTS: Sp1 expression was observed in the ectoderm and lens vesicle as early as E10.5. Both Sp1 protein and mRNA were abundant in the corneal basal epithelium and keratocytes until P11. Their levels were markedly reduced at P15, right after eyelid opening, and declined further between P15 and P60. In those mice bred in the dark, Sp1 was evident in the cornea at P0. The Sp1 level gradually increased until P11 and was decreased at P15. This expression pattern was nearly identical in mice bred either in a light/dark cycle or in the dark. The Sp1 level in the central lens epithelium was much lower than that in the cornea from E15.5 to late stages. CONCLUSIONS: The present study indicates that Sp1 expression is developmentally regulated, providing a basis for further investigations on the regulation of the Sp1 gene during the course of corneal development and in diseases such as keratoconus.
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Córnea/embriología , Regulación del Desarrollo de la Expresión Génica/fisiología , Factor de Transcripción Sp1/genética , Animales , Córnea/crecimiento & desarrollo , Córnea/metabolismo , Sustancia Propia/embriología , Sustancia Propia/metabolismo , Endotelio Corneal/embriología , Endotelio Corneal/metabolismo , Epitelio Corneal/embriología , Epitelio Corneal/metabolismo , Femenino , Técnicas para Inmunoenzimas , Hibridación in Situ , Masculino , Ratones , Ratones Endogámicos C57BL , Embarazo , ARN Mensajero/metabolismo , Factor de Transcripción Sp1/metabolismoRESUMEN
The purpose of this study was to investigate the histomorphometric change in the normal development of human fetal corneal endothelial cells. Eighty one human fetal corneas, ranging from 12 to 40 weeks of gestation, were examined. For determination of gross parameters, corneal diameter and height were measured. Then the corneal endothelium including Descemet's membrane was stained with hematoxylin-eosin using a flat preparation method. In addition to histologic examination under the light microscope, computer-assisted image analysis was performed to determine the cell area, coefficient of variation in cell area and cell density, in both central and peripheral cornea, from each specimen. Total cell count per cornea was obtained by multiplying endothelial cell density by corneal surface area. Linear and nonlinear regression analysis of gestational age and each parameter were used to model corneal endothelial development during the prenatal period. Fetal cornea grows rapidly throughout the prenatal period. During the same period, mean cell area and total cell count also increases gradually, but there is a steep increase in the total cell count in the early period and of the cell area in the late period. The mean cell density decreases rapidly from 16 015 to 6167 cell x mm(-2). There was no significant difference in all parameters except cell density, between the central and peripheral cornea and the difference in cell density was only 2%. In the early prenatal period, there is a rapid increase of total cell count by mitosis, whereas in the late period enlarged endothelial cells cover the rapidly widening inner corneal surface without a significant change in the total cell count.
Asunto(s)
Endotelio Corneal/embriología , Recuento de Células , Tamaño de la Célula , Colorantes , Desarrollo Embrionario y Fetal , Eosina Amarillenta-(YS) , Edad Gestacional , Hematoxilina , Humanos , Procesamiento de Imagen Asistido por Computador , Modelos Lineales , Análisis de RegresiónRESUMEN
The anterior segment of the vertebrate eye is constructed by proper spatial development of cells derived from the surface ectoderm, which become corneal epithelium and lens, neuroectoderm (posterior iris and ciliary body) and cranial neural crest (corneal stroma, corneal endothelium and anterior iris). Although coordinated interactions between these different cell types are presumed to be essential for proper spatial positioning and differentiation, the requisite intercellular signals remain undefined. We have generated transgenic mice that express either transforming growth factor (alpha) (TGF(alpha)) or epidermal growth factor (EGF) in the ocular lens using the mouse (alpha)A-crystallin promoter. Expression of either growth factor alters the normal developmental fate of the innermost corneal mesenchymal cells so that these cells often fail to differentiate into corneal endothelial cells. Both sets of transgenic mice subsequently manifest multiple anterior segment defects, including attachment of the iris and lens to the cornea, a reduction in the thickness of the corneal epithelium, corneal opacity, and modest disorganization in the corneal stroma. Our data suggest that formation of a corneal endothelium during early ocular morphogenesis is required to prevent attachment of the lens and iris to the corneal stroma, therefore permitting the normal formation of the anterior segment.
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Cámara Anterior/anomalías , Cámara Anterior/embriología , Ectodermo/fisiología , Endotelio Corneal/embriología , Factor de Crecimiento Epidérmico/fisiología , Cristalino/embriología , Factor de Crecimiento Transformador alfa/fisiología , Animales , Cadherinas/análisis , Cadherinas/genética , Cristalinas/genética , Modelos Animales de Enfermedad , Desarrollo Embrionario y Fetal , Endotelio Corneal/anomalías , Factor de Crecimiento Epidérmico/genética , Receptores ErbB/genética , Regulación del Desarrollo de la Expresión Génica , Humanos , Ratones , Ratones Endogámicos ICR , Ratones Transgénicos , Factor de Crecimiento Transformador alfa/genéticaRESUMEN
PURPOSE: To count the number of the corneal endothelial cells per unit of tissue area in 25 human fetal eyes ranging from 12-40 weeks of gestation with the histologic method. METHODS: The endothelium including Descemet's membrane was stained with hematoxylin-eosin by the flat preparation method. We photographed the endothelium using light microscopy. The number of nuclei was counted on each photograph. A calibrated micrometer was photographed with the light microscopy, and this was used to measure the number of corneal endothelial cells per square millimeter. RESULTS: The prenatal endothelial cell density of the human cornea decreases rapidly from 14,095 cells/mm2 (12 weeks of gestation) to 6,820 cells/mm2 (40 weeks of gestation). CONCLUSION: The estimate of the endothelial cell density at 12 weeks of gestation is twofold higher than the estimate at 40 weeks of gestation.
Asunto(s)
Endotelio Corneal/citología , Endotelio Corneal/embriología , Feto/citología , Recuento de Células , Técnicas Citológicas , Edad Gestacional , HumanosRESUMEN
Current thinking on the embryological origin of human corneal endothelium has it that this cellular population stems from neural crest precursors. There are arguments in support of this assumption but equally persuasive ones against it. We present a discussion of the evidence for and against a neural crest origin for human corneal endothelial cells. In suggesting that caution be applied to extrapolating from non-human work, we would question the fallibility of the current thinking on this subject. To denote human corneal dystrophies as neurocristopathies may be a premature assumption.
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Distrofias Hereditarias de la Córnea/embriología , Cresta Neural/embriología , Animales , Embrión de Pollo , Endotelio Corneal/embriología , Humanos , Melanocitos/citología , Codorniz/embriologíaRESUMEN
PURPOSE: To investigate whether the human corneal keratocyte density changes during aging. METHODS: Comparative data on keratocyte and endothelial cell density (ECD) were obtained from 178 normal corneas (89 persons ranging in age from 30 weeks of gestation to 90 years). Keratocyte density was quantified by using biochemical measurements of the stromal DNA/ mass content within the central 7-mm diameter zone (sDNA) (1 U equals 1 microgram DNA per milligram of dry tissue weight), whereas central ECD was assessed after alizarin red staining. RESULTS: In the first decade of life, there was a mean sDNA of 1.64 +/- 0.29 U, corresponding to 6.22 +/- 1.1 x 10(4) keratocytes per mm3. A direct correlation between keratocyte density and donor age was found (r = -0.49; p < 0.0001) with a physiologic decline of 0.3% per year throughout life (density = 6.30 x 10(4) keratocytes per mm3-190 x age). A similar decrease of 0.3% per year was observed in the ECD during adulthood, whereas the annual decline was 2.9% during infancy and childhood. The interindividual variation in keratocyte density was of the same magnitude as that seen in ECD. Moreover, keratocyte density was positively correlated with ECD (r = 0.23; p < 0.001); however, after correcting for age by multiple regression analysis, this correlation disappeared, indicating that keratocytes and endothelial cells form distinct cell populations. CONCLUSIONS: The study demonstrates a linear loss of human corneal keratocytes as a function of age, a loss that parallels the well established decline in ECD.
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Envejecimiento/fisiología , Córnea/citología , Endotelio Corneal/citología , Fibroblastos/citología , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Recuento de Células , Niño , Preescolar , Córnea/embriología , Córnea/crecimiento & desarrollo , Sustancia Propia/química , ADN/análisis , Replicación del ADN , Endotelio Corneal/embriología , Endotelio Corneal/crecimiento & desarrollo , Femenino , Humanos , Lactante , Masculino , Persona de Mediana Edad , Donantes de TejidosRESUMEN
Using an organotypic culture method, we evaluated the biocompatibility of two kinds of intraocular lenses: conventional poly(methyl methacrylate) (PMMA) and heparin-surface-modified (HSM) PMMA. Chicken corneal endothelium from embryos incubated for 14 days was placed on an agar medium and covered with one of three types of materials: PMMA, HSM PMMA, and a control, Thermanox. Experiments at five different times measured cell migration, cell multiplication, and cell adhesion. Scanning electron microscopy showed a low level of corneal endothelial adhesion on the HSM IOL surface. There was a significant difference between the HSM and untreated lenses in migration surface and cell density, with the HSM lenses having better biocompatibility.
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Materiales Biocompatibles , Endotelio Corneal/ultraestructura , Heparina , Lentes Intraoculares , Animales , Adhesión Celular , División Celular , Movimiento Celular , Embrión de Pollo , Endotelio Corneal/embriología , Endotelio Corneal/fisiología , Ensayo de Materiales , Metilmetacrilato , Metilmetacrilatos , Técnicas de Cultivo de Órganos/métodosRESUMEN
Embryos of the clearnose skate, Raja eglanteria, develop in sea water at 20-22 degrees C, hatching after 82 +/- 4 days (Luer and Gilbert, Environ. Biol. Fishes, 13:161-171, 1985). Eyes develop as steadily enlarging spheres whose corneas have the same radius of curvature as the sclera. The cornea begins development as a 2-cell thick epithelium beneath which by Day 12 there is only a basal lamina and a wispy matrix separating it from the underlying lens. This matrix, modified by Day 16, is displaced on Day 22 by a few orthogonal plies of fibrillar primary stroma. Ply number increases to at least 13 by Day 30, reaching the final number of 20 +/- 2 by Day 42. Stromal fibroblasts (keratocytes) appear at the corneal periphery by Day 22, and in increased numbers by Day 30, a time at which no keratocytes are seen in the central stroma. However, by Day 40, many fibroblasts are present at the corneal periphery, invading the primary stroma between plies, occasionally reaching even the central cornea. By Day 53, keratocytes are present between all plies, from corneal periphery to center. Thickness of each ply in this secondary stroma increases, but the number of plies remains the same as in the primary stroma. Bowman's layer, non-invaded matrix beneath the epithelial basal lamina, is not evident until Day 53. Sutural fibers, first seen on Day 22, originate in the corneal epithelial basal lamina, traversing perpendicularly the plies of the primary stroma. Sutural fibers persist throughout development of the secondary stroma and into adulthood. In contrast to chicks, skate corneas remain transparent throughout development, and never form an endothelium.
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Córnea/embriología , Endotelio Corneal/embriología , Rajidae/embriología , Animales , Córnea/ultraestructura , Endotelio Corneal/ultraestructura , Células del Estroma/ultraestructuraRESUMEN
The main bulk of corneal endothelial cells is formed during early embryonic development. In the course of development, two-layered endothelium becomes single-layered; the cell layer consists of rosette-like structures formed of a central cell (9 to 10% of all endothelial cells) surrounded by peripheral cells. The central cell is not a stem cell, and the peripheral cells are not its descendants. The presence in corneal endothelium of a constant number of peripheral cells surrounding the central cell, as in other epithelia with different proliferative potential, is evidence that the central cells can organize the peripheral cells and exercise control over them.
Asunto(s)
Endotelio Corneal/embriología , División Celular , Núcleo Celular/ultraestructura , Endotelio Corneal/ultraestructura , Edad Gestacional , Humanos , Microscopía Electrónica , MitosisRESUMEN
The ultra-microstructure of the human corneal endothelium was examined by scanning and transmission electron microscopy. The samples were corneas of 26 human eyes taken from fetuses of 5-22 weeks gestation and a newborn 10 months after birth. Corneal endothelium appeared at the seventh or eighth week after gestation. Initially, they formed an irregular structure of two to three layers. From the 17th week of gestation they formed a single layer, and assumed the form of a cuboidal epithelium. Scanning and transmission electron microscopy showed numerous microvilli protruding towards the anterior chamber. Within the microvilli uniform microtubules were observed. By the 20th week, these microvilli disappeared, and subsequently, a single long narrow cilium appeared in the center of each cell. Each cilium had an axial filament complex structure. This cilium involuted as development progressed, and was barely visible by the 10th month after birth. The significance of this cilium is not clear.