The role of calcium in depigmentation of iris epithelial cells during cell-type conversion

Molecular Signatures Integral to Natural Reprogramming in the Pigment Epithelium Cells after Retinal Detachment in Pleurodeles waltl

The reprogramming of retinal pigment epithelium (RPE) cells into retinal cells (transdifferentiation) lies in the bases of retinal regeneration in several Urodela. The identification of the key genes involved in this process helps with looking for approaches to the prevention and treatment of RPE-related degenerative diseases of the human retina. The purpose of our study was to examine the transcriptome changes at initial stages of RPE cell reprogramming in adult newt Pleurodeles waltl. RPE was isolated from the eye samples of day 0, 4, and 7 after experimental surgical detachment of the neural retina and was used for a de novo transcriptome assembly through the RNA-Seq method. A total of 1019 transcripts corresponding to the differently expressed genes have been revealed in silico: the 83 increased the expression at an early stage, and 168 increased the expression at a late stage of RPE reprogramming. We have identified up-regulation of classical early response genes, chaperones and co-chaperones, genes involved in the regulation of protein biosynthesis, suppressors of oncogenes, and EMT-related genes. We revealed the growth in the proportion of down-regulated ribosomal and translation-associated genes. Our findings contribute to revealing the molecular mechanism of RPE reprogramming in Urodela.

Immunocytochemical study of extracellular matrix components during lens and neural retina regeneration in the adult newt

We have conducted an immunocytochemical study of fibronectin, laminin, heparan sulfate proteoglycans and nidogen-entactin during lens and neural retina regeneration in the adult newt from 0 to 60 days. In the normal eye, fibronectin was detected in the corneal stroma and Descemet's membrane, in dorsal and ventral irises and lens capsule but not in Bowman's membrane of the cornea. In normal neural retina, fibronectin was found in Bruch's and inner limiting membranes. Heparan sulfate proteoglycans gave a slight signal in both irises and the lens capsule. Nidogen-entactin distribution in the cornea was similar to that of fibronectin; it was absent from the stroma of both irises, and the signal was weak in the pigmented iris epithelium. Nidogen-entactin was not detected in the lens capsule and inner limiting membrane of the neural retina but was present in Bruch's membrane. During the first 15 days of lens regeneration, fibronectin and nidogen-entactin decreased but did not disappear from the pupillary margin of both irises, and no signal was obtained for laminin and heparan sulfate proteoglycans. From day 15 to day 60 fibronectin and nidogen-entactin increased in both irises and lens capsule. The signal for laminin was restricted to the lens capsule. Heparan sulfate proteoglycans gave a slight signal in both irises and in the lens capsule. During the first 25 days of neural retina regeneration, fibronectin was the first to appear in Bruch's membrane and the cell border of the new neuroepithelium and remained during the entire process. Laminin appeared after 41 days in the inner limiting and Bruch's membranes, but by day 50 it appeared as a weak signal only in the inner limiting membrane. Heparan sulfate proteoglycans were not detected at any of the regeneration stages studied. Nidogen-entactin was only detected in Bruch's membrane and around the cells and blood vessels of the new neural retina. Later it was detected in the inner limiting membrane but not in Bruch's membrane. Thus, the results obtained showed that extracellular matrix components do change during both lens and neural retina regeneration. These changes may play an important role during both regenerating processes.

Macrophage mobilization and morphology during lens regeneration from the iris epithelium in newts: studies with correlated scanning and transmission electron microscopy

The lens was removed from both eyes of adult newts (Notophthalmus viridescens), and the eyes were fixed in Karnovsky's fixative every 2 days 0-20 days after operation. Anterior half-eyes were prepared by standard procedures for scanning electron microscopy of the surface. Before fixation, the posterior iris surface was cleaned of adhering vitreous mechanically with forceps or by treatment with bovine testicular hyaluronidase or with hyaluronidase and collagenase. Some specimens were cryofractured in buffer or ethanol transverse to the mid-dorsal iris, and the fractured surface viewed with scanning electron microscopy (SEM). Cells with various combinations of ridges, blebs, filopodia, and lamellipodia were observed adhering to the posterior surface of the iris by 6 days after lentectomy. These cells, which exhibited the surface characteristics of macrophages, became more numerous in specimens fixed after longer intervals. Invasion of the iris epithelium was observed in a cryofractured specimen. After observations with SEM, selected specimens were embedded in plastic and sectioned for study with transmission electron microscopy (TEM). The cells on the iris surface had the cytological characteristics of macrophages, and other macrophages were located within the iris epithelium. In specimens fixed 16 or more days after lentectomy, a bulging lens vesicle was regenerating from the dorsal pupillary margin of the iris. Macrophages were absent or few on the surface of this developing lens but remained scattered over the adjoining iris. Roles that might be played by these macrophages during the transdifferentiation of iris epithelium into lens are discussed.

Fibronectin distribution during cell type conversion in newt lens regeneration

The distribution of fibronectin during the cell type conversion from iris into lens that occurs in newt lens regeneration was studied by immunofluorescence. Newts were lentectomized and irises at different stages of dedifferentiation and redifferentiation were examined using as a probe a rabbit antiserum prepared to Xenopus plasma fibronectin. In the normal iris, fibronectin is predominantly located at the basal surface of the pigmented iris epithelial cells. During activation and early dedifferentiation fibronectin staining is progressively displayed at the basolateral and apical surface of the depigmenting cell, to eventually surround the surface of the dedifferentiated cells. As cells redifferentiate into lens fibers, staining for cell surface fibronectin decreases and is displayed mainly in the nascent lens capsule. Fibronectin deposition may be associated with the formation of intercellular spaces during dedifferentiation. The fibronectin-rich extracellular matrix could be important in cell reprogramming.

Cell type expression mediated by cell cycle events, and signaled by mitogens and growth inhibitors

It is initially pointed out that the majority of factors that induce cell type expression in mature precursor cells are either mitogens or growth inhibitors. On the basis of available data, a theoretical model of regulation of cell type expression for each group of factors is proposed. In model A the mitogen affects the expression of cell type through the positive control of cell cycle progression, while in model B the growth inhibitor induces the negative control of cell cycle progression, which in its turn causes the cell type expression. In connection with those two models, various systems of cell type expression are classified into three groups. In model A systems, the cell lineage has an option of autotypic and allotypic cell types. The former is expressed in the absence of added mitogen, and the latter is expressed in its presence. In model B systems the cell lineage-specific cell type is expressed by the negative cell cycle control induced by the growth inhibitor. In model A-B systems both mitogen and inhibitor are needed in tandem for the expression of a cell type. The second major point made is that the expression of cell type follows the negative control of cell cycle progression even in model A systems. However, in this system the control occurs spontaneously. This suggests that the negative control is essential for cell type expression in all systems, and directly precedes the expression. In contrast, the positive control induced by exogenous mitogen is not required in the expression in model B systems or in that of autotypic cell types in model A systems. The third point is that on the basis of the hypothesis of replication-transcription coupling, proposed by Sauer and colleagues, it is speculated that the pattern of early-replicating genes may be functioning as the potential gene transcription pattern for cell type expression in precursor cells. If this pattern is perpetuated through cell generations, the original cell type specificity of the precursor cell lineage should be maintained. If this pattern is modified by the positive control of cell cycle progression in model A systems, the potential transcriptional pattern for the allotypic pathway may emerge. Furthermore, it is proposed that the realization of the potential pattern may depend on a signal, informing the completion of the negative control of cell cycle progression. Thus in all cell lineages, when the negative cell cycle control is completed, chromatin receives this signal, and the potential transcription pattern is converted into cell type differentiation.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of catecholamines and adenosine on the induction of morphological alterations and depigmentation of newt iris epithelial cells in vitro

Catecholamines and adenosine have a stimulating effect on the process of dedifferentiation of cultured iris epithelial cells (IECs) from the adult newt Notophthalmus viridescens. Micromolar concentrations of adrenergic ligands such as isoproterenol, norepinephrine, and epinephrine induced marked morphological alterations culminating in the stellate configuration and depigmentation of IECs. Dopamine at 100 microM or higher induced the morphological response, while serotonin was ineffective. The morphological change was transient, requiring 80-90 min for maximum induction, and only a fraction of the cells was responsive. The response was blocked by beta-adrenergic antagonists, such as propranolol and alprenolol, but not by alpha-adrenergic blockers. Adenosine at 10 microM, or higher, also induced morphological alterations of IECs. The effect of adenosine was partially blocked by various adenosine receptor antagonists. The effect of isoproterenol and norepinephrine on the induction of morphological alterations was potentiated by adenosine. The release of melanosomes from IECs was increased in the presence of catecholamines and adenosine. Catecholamines and adenosine at 10 microM increased the intracellular levels of cAMP of dedifferentiating dorsal irides. The increase in cAMP levels induced by isoproterenol was inhibited by propranolol and the adenosine receptor antagonist 5'-deoxy-5'-methyl thioadenosine (MTA) partially blocked the effect of adenosine. Our results suggest that adrenergic hormones may be coupled to a beta-adrenergic adenylate cyclase system. The presence of an adenosine receptor is also suggested by the results. Our data strongly support previous work in which cAMP and substances related to it induced morphological alterations and depigmentation of IECs. It is proposed that catecholamines and adenosine may participate in the regulation of dedifferentiation during the transdifferentiation of IECs into lens cells.

The antitumor drug 3-nitrobenzothiazolo(3,2-a)quinolinium chloride (NBQ): effects on lens regeneration and interaction with DNA of Notophthalmus viridescens

We have studied the effect of 3-nitrobenzothiazolo(3,2-a)quinolinium (NBQ) on the regeneration of the lens in adult newt Notophthalmus viridescens. NBQ has marked cytotoxic effects in tumor cells, intercalates DNA, and was found to enhance lens regeneration. Newt liver DNA was isolated, and the thermal denaturation temperature (Tm) determined to be 76.6% +/- 0.8%. The G-C content was determined to be 44.0% +/- 0.4% and 45.0% +/- 0.1%. Parameters of NBQ binding to newt DNA were determined by spectrophotometric methods and compared with those obtained for calf thymus and Micrococcus lysodeikticus. The association constant, K(o), was found to be 1.1 x 10(+5) M-1 with a site-size parameter, n, of 8.7 nucleotides. No explanation is apparent for the paradoxical stimulation of lens regeneration.

Hyaluronic acid production and hyaluronidase activity in the newt iris during lens regeneration

The process of lens regeneration in newts involves the dedifferentiation of pigmented iris epithelial cells and their subsequent conversion into lens fibers. In vivo this cell-type conversion is restricted to the dorsal region of the iris. We have examined the patterns of hyaluronate accumulation and endogenous hyaluronidase activity in the newt iris during the course of lens regeneration in vivo. Accumulation of newly synthesized hyaluronate was estimated from the uptake of [3H]glucosamine into cetylpyridinium chloride-precipitable material that was sensitive to Streptomyces hyaluronidase. Endogenous hyaluronidase activity was determined from the quantity of reducing N-acetylhexosamine released upon incubation of iris tissue extract with exogenous hyaluronate substrate. We found that incorporation of label into hyaluronate was consistently higher in the regeneration-activated irises of lentectomized eyes than in control irises from sham-operated eyes. Hyaluronate labeling was higher in the dorsal (lens-forming) region of the iris than in ventral (non-lens-forming) iris tissue during the regeneration process. Label accumulation into hyaluronate was maximum between 10 and 15 days after lentectomy, the period of most pronounced dedifferentiation in the dorsal iris epithelium. Both normal and regenerating irises demonstrated a high level of endogenous hyaluronidase activity with a pH optimum of 3.5-4.0. Hyaluronidase activity was 1.7 to 2 times higher in dorsal iris tissue than in ventral irises both prior to lentectomy and throughout the regeneration process. We suggest that enhanced hyaluronate accumulation may facilitate the dedifferentiation of iris epithelial cells in the dorsal iris and prevent precocious withdrawal from the cell cycle. The high level of hyaluronidase activity in the dorsal iris may promote the turnover and remodeling of extracellular matrix components required for cell-type conversion.

Conversion of iris epithelial cells as a model of differentiation control

It has been shown that, upon lentectomy or in culture, iris epithelial cells (IECs) of adult newts become converted into lens cells, and this conversion is the basic event of lens regeneration in newts. Whether in situ or in cell culture, the conversion requires the passage of a specific number of cell cycles. The progeny of IECs which fails to traverse this cell-cycle number redifferentiates as IECs in situ. The passage through cell cycles of IECs is associated with progressive alterations of cytoplasm and cell surface, during which the original state of differentiation disappears (dedifferentiation). It is speculated that the altered state of cells caused by proliferation leads to the appearance of factors which interact with the genome and switch the gene activation pattern to that of the lens cell. In this model, developmental controls are geared to the cell-cycle progression and not directly to the activation of lens-characteristic genes. A number of points are raised which speak against the long-held idea that a factor from neural retina induces lens differentiation in IECs. It is proposed that the retinal factor plays the role of growth factor which is essential in the conversion in situ, but not required in the conversion in cell culture. The proposed model is compared with reprogramming of differentiation of some cell lines by cytidine analogs and with ontogenic systems of differentiation control.