Macrophage activity in Wolffian lens regeneration

The cell type mainly involved in the phagocytic uptake of melanosomes from iris epithelial cells during Wolffian lens regeneration in the adult newt is identified on the basis of electron and light microscopic evidence as a macrophage of monocytic origin. Appearance of macrophages in iris and ciliary epithelia following lentectomy is a part of leucocytic infiltration of the area, in which granulocytes, mast cells, and other cell types also participate. The general pattern of leucocytic infiltration was studied as a function of time after lentectomy. Infiltration of the iris epithelium by macrophages is reduced when most of the melanosomes have been removed from the cytoplasm of the epithelial cells and finally ceases when depigmentation has been completed. The possibility that an immune mechanism mediated by macrophages is involved in dedifferentiation of iris epithelial cells is discussed.     

Cellular and molecular background of Wolffian lens regeneration

Based on studies of wolffian lens regeneration in the newt, in which the lens can be regenerated from the iris pigmented epithelium, we have shown by cell culture studies that the capacity of lens transdifferentiation is not limited to the newt cells, but widely conserved in pigmented epithelial cells (PECs) of chick and quail embryos and even of human fetuses. Recently, we have established a unique in vitro model system of chick embryonic PECs. In this culture system we are able to control each step of transdifferentiation from PECs into lens cells by regulating culture conditions and to produce a homogeneous cell population with potential for synchronous differentiation into either lens or pigment cell phenotype. These multipotent (at least bipotent) cells showed cellular characteristics resembling neoplastic cells in many ways. They did not express both lens and pigment cell specific genes analyzed so far, except δ-crystallin gene, which is expressed in developing lens of chick embryos. It has been proved by application of cell culture procedures of the system that PECs dissociated from fully-grown human eyes readily transdifferentiated into lens phenotypes in the manner observed in chick embryo PECs. In addition, we could predict that molecules detected in either cell surface or intercellular space stabilized the differentiated state of PECs in the newt and that the loss of these molecules might be one of the key steps of lens regeneration from the iris epithelium.     

Influence of indomethacin on lens regeneration in the newt notophthalmus viridescens

Summary Following lentectomy newts were injected with indomethacin in a variety of carrier solutions at doses ranging from 1.2–120 mg/kg body weight every other day for 15–17 days. The results show that injection of this drug according to the regimen used has no significant effect on regeneration of the lens. The data suggest, but do not prove, that prostaglandins may not play a major role in the early phases of lens regeneration in the newt.     

Effect of bovine pituitary hormone preparations on newt lens regeneration in vitro: stimulation by thyrotropin

The anterior lobe of the pituitary gland can stimulate lens regeneration from the dorsal iris in the newt Notophthalmus viridescens. We have studied the effect of pituitary hormone preparations on this process. Dorsal irises were cultured for 20 days in diluted Medium 199 supplemented with 10% fetal calf serum. Bovine thyrotropin TSH-B8 at concentrations of 30 to 3000 μg/ml significantly stimulated lens regeneration in these dorsal irises. Well-developed lenses, up to stage 9, were formed, in which γ-crystallin, a protein specific for lens fibers of young lenses, was detected by immunofluorescence. Additionally, the mitotic index was 5.5 times elevated in these explants when compared to their controls. Lutropin LH-B10 at concentrations of 30 to 3000 μg/ml, prolactin PRL-B4 at concentrations of 23 to 1600 μg/ml, and porcine adrenocorticotropin ACTH-6002 at concentrations of 3 to 300 μg/ml did not stimulate lens regeneration. A weak stimulation of lens formation was observed in iris cultures with 2700 μg/ml of follitropin FSH-B1 or 3000 μg/ml somatotropin GH-B18, but not at concentrations of 30 μg/ml. Our results suggest that the inherent ability of the dorsal iris to form lens can be activated by the bovine thyrotropin preparation TSH-B8.     

Signaling during lens regeneration

The newt is one of the few organisms that is able to undergo lens regeneration as an adult. This review will examine the signaling pathways that are involved in this amazing phenomenon. In addition to outlining the current research involved in elucidating the key signaling molecules in lens regeneration, we will also highlight some of the similarities and differences between lens regeneration and development.     

干细胞与晶状体再生

白内障摘除联合人工晶状体植入术是目前治疗白内障的唯一有效措施。然而,人工晶状体作为替代材料,仍然存在一些如屈光调节力差以及术后眩光等未能克服的缺陷。寻找更理想的晶状体替代物及低等两栖类动物（如蝾螈）强大的晶状体再生能力,为晶状体再生的研究提供了原动力和依据。近年来,人们已探索出将胚胎干细胞/诱导的多能干细胞在体外诱导分化为类晶状体样结构的培养方法,为白内障的治疗开辟了新的思路。晶状体再生的研究为探索晶状体正常发育机制及晶状体疾病的发生和防治提供了新的平台。晶状体再生的成功也将为白内障的防治带来里程碑性的突破。本文拟总结晶状体正常发育过程及其调控机制,回顾国内外对晶状体体内再生能力的研究成果,并对目前人们探索利用胚胎干细胞和诱导的多能干细胞再造晶状体的研究进展作一概述,希望对干细胞与晶状体再生的后续相关研究提供一定的借鉴。     

Effect of vitamin A on lens regeneration in pigs

Intraperitoneal injections of vitamin A (0.5 ml of 1500 IU/ml) to lentectomized pigs on alternate days up to 60 th day after lentectomy induced lens regeneration in not only 10 days old young ones but also in 40 and 100 days old pigs. Lens regeneration did not occur even in a single case of control groups. In shape, size, transparency and histological features regenerated lenses were similar to normal intact lenses. The experimental model is the first to show that mitogenic and dedifferentiate activity of vitamin A can induce iris pigmented epithelial cells to trans-differentiate into new lens in pigs.     

A newt's eye view of lens regeneration

In this paper we describe the basic process of lens regeneration in adult newt and we pinpoint several issues in order to obtain a comprehensive understanding of this ability, which is restricted to only a few salamanders. The process is characterized by dynamic changes in the organization of the extracellular matrix in the eye, re-entering of the cell cycle and dedifferentiation of the dorsal iris pigment epithelial cells. The ability of the dorsal iris to contribute to lens regeneration is discussed in light of iris-specific gene expression as well as in relation to factors present in the eye.     

A novel role of the hedgehog pathway in lens regeneration

Lens regeneration in the adult newt is a classic example of replacing a lost organ by the process of transdifferentiation. After lens removal, the pigmented epithelial cells of the dorsal iris proliferate and dedifferentiate to form a lens vesicle, which subsequently differentiates to form a new lens. In searching for factors that control this remarkable process, we investigated the expression and role of hedgehog pathway members. These molecules are known to affect retina and pigment epithelium morphogenesis and have been recently shown to be involved in repair processes. Here we show that Shh, Ihh, ptc-1, and ptc-2 are expressed during lens regeneration. The expression of Shh and Ihh is quite unique since these genes have never been detected in lens. Interestingly, both Shh and Ihh are only expressed in the regenerating and developing lens, but not in the intact lens. Interfering with the hedgehog pathway results in considerable inhibition of the process of lens regeneration, including decreased cell proliferation as well as interference with lens fiber differentiation in the regenerating lens vesicle. Down-regulation of ptc-1 was also observed when inhibiting the pathway. These results provide the first evidence of a novel role for the hedgehog pathway in specific regulation of the regenerating lens.     

Retina and lens regeneration in anuran amphibians

Anuran amphibians can regenerate the retina through differentiation of stem cells in the ciliary marginal zone and through transdifferentiation of the retinal pigmented epithelium. By contrast, the regeneration of the lens has been demonstrated only in larvae of species belonging to the Xenopus genus, where the lens regenerates through transdifferentiation of the outer cornea. Retinal pigmented epithelium to neural retina and outer cornea to lens transdifferentiation processes are triggered and sustained by signaling molecules belonging to the family of the fibroblast growth factor. Both during retina and lens regeneration there is a re-activation of many of the genes which are activated during development of the eye, even though the spatial and temporal pattern of gene expression is not a simple repetition of that found in development.     

Influence of denervation on the regeneration of Pleurodele limbs

Abstract. A cytophotometric study of Feulgen-stained mesenchymal cell nuclei from regeneration blastemas of both innervated and denervated limbs over the 1st 7 days following the midbud stage showed a diminution of the percentage of cells in the S + G₂ phases and a corresponding augmentation of the percentage of cells in the G₀+ G₁ phases. This change, which was temporally correlated with the redifferentiation of the innervated blastemas, was greater in denervated blastemas, even though they do not redifferentiate. From these results, it is concluded that the denervation of midbud blastemas brings about either an extension of the G₁ phase or an exiting from the cell cycle to G₁ (G_0–1), or both phenomena.     

Regulation of Wolffian duct development

Wolffian ducts (WDs) are the embryonic structures that form the male internal genitalia. These ducts develop in both the male and female embryo. However, in the female they subsequently regress, whereas in the male they are stabilised by testosterone. The WDs then develop into separate but contiguous organs, the epididymis, vas deferens and seminal vesicles. Recently, considerable progress has been made in identifying genes that are involved in these different stages of development which is described in this review. In addition, WD development in (atypical forms of) cystic fibrosis and intersex disorders, such as the complete androgen insensitivity syndrome, 17beta-hydroxysteroid dehydrogenase deficiency and LH-receptor defects, is discussed. The apparent increase in male reproductive tract disorders is briefly discussed from the perspective of the potential endocrine-disrupting effects of the numerous chemicals in the environment to which the developing male foetus can be exposed.