Synergistic Effects of Adenosine and Compounds Related to Adenosine 3′: 5′-cyclic Monophosphate on Dedifferentiating Iris Epithelial Cells in Culture

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.

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.

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.

Orchestration of tooth movement

Recent advances in the art and mechanics of delivering orthodontic forces have achieved greater precision and control of tooth movement. The exact mechanism by which these forces orchestrate tooth movement is not thoroughly understood. An accurate understanding and precise control over the factors responsible for initiating and carrying out the tissue reaction will ultimately optimize the rate of tooth movement. An integrated hypothetical model for the mechanism of tooth movement is discussed here. This model is based on the most recent body of information available to explain how various stimuli affect bone cells. The roles played by piezoelectric responses, prostaglandin production, and biochemical factors are discussed, with particular emphasis on their importance and contribution in terms of maximizing the rate of tooth movement. The intelligent use of this knowledge will permit us to modify the orthodontic appliance and treatment regimen in order to achieve an optimum tissue response.

Intracellular levels of adenosine 3':5'-cyclic monophosphate in the dorsal iris of the adult newt, during lens regeneration

The intracellular levels of adenosine 3':5'-cyclic monophosphate (cAMP) were measured in the dorsal iris of the adult newt, during the first 20 days of lens regeneration. It was found that by day 2 after lens removal there is a significant drop in the levels of cAMP. After day 2 the levels of the nucleotide increase and by day 3 they are higher than those detected on day 0. The levels of cAMP remain high up to day 8. From day 8 to day 9 there is a second drop. From day 9 to day 20 the levels of cAMP did not differ significantly from the value obtained for day 0, except for days 10, 12, and 15. The period of high levels of cAMP coincides with the period of depigmentation of iris epithelial cells, the key event of lens regeneration.

The influence of hormones and other substances on lens regeneration in vitro

Culturing the dorsal iris epithelium of a newt with a pituitary gland in organ culture greatly enhances the ability of the iris epithelium to produce advanced lens regenerates in vitro. In an attempt to elucidate the mechanism by which the pituitary enhances lens regeneration irido-corneal complexes from adult newts were cultured in medium to which various substances had been added either singly or in numerous combinations. Prolactin, insulin, hydrocortisone, and thyroxine failed to enhance the production of advanced lens regenerates in any of the doses or combinations tested. Similarly, addition of 50 microgram/ml of sodium or calcium ascorbate had no effect on the progress of lens regeneration in vitro. Addition of dibutyryl cyclic-AMP caused an inhibition of depigmentation and regeneration at high doses. The results of these experiments show that the effects of the pituitary cannot be duplicated by hormones which other authors have asserted to be beneficial to limb or tail regenerates in vitro. The results with cyclic AMP suggest that prolonged exposure to high doses of cyclic AMP inhibit regeneration and indicate that further studies on the fluctations in cyclic AMP levels throughout the process of lens regeneration must be done.