In Vivo and in Vitro Experimental Analysis of Lens Regeneration in Larval Xenopus laevis

Abstract

After lentectomy of larval Xenopus laevis, the outer cornea undergoes tissue transformation resulting in formation of a new lens. This lens regeneration is triggered and sustained by neural retina. In the present study, lens-forming transformation of the outer cornea was completed in vitfo when the outer cornea was cultured within the lentectomized eye-cup. Well-differentiated lens fiber cells, which showed positive immunofluorescence for total crystallins, were also formed when the outer cornea was cultivated with the retina. No lens tissue was formed when the cornea was cultured alone. Lens-forming transformation, originating from the cornea three and five days after lentectomy, completely regressed when the tissue was isolated in vitro. Fom the present and previous findings, we concluded that, the interaction of corneal cells with the retina plays a decisive role in lens regeneration in situ.

Control mechanisms of in vitro lens transdifferentiation ofXenopus laevisouter cornea

“…These results were consistent with those we previously reported (Bosco et al, 1993b(Bosco et al, , 1997.…”

“…It can be isolated and cultivated for several days and under these experimental conditions the outer cornea maintains its typical bilayered epithelial structure without showing any sign of lens-transdifferentiation. Lensforming transformations originating from the cornea after lentectomy completely regress when left out of the action of the retinal factor(s) or •when implanted between the outer and inner cornea of host larvae or isolate in vitro (Bosco et al, 1986(Bosco et al, , 1993b. On the contrary, well-differentiated lens fibre cells, which show positive immunofluorescence for total crystallins are formed when the outer cornea is cultivated with neural retina.…”

“…During in vitro lens-transdifferentiation the corneal cells of Xenopiis (Bosco et al, 1993b(Bosco et al, , 1997 show the same series of cytological changes observed during lens ontogenesis (Papaconstantinou, 1967) and in vivo lens regeneration (Freeman, 1963): enlargement of nuclei and nucleoli, massive increase of ribosomal population (cytoplasm basophilia), cell elongation, gradual loss of basophilic properties and acquisition of acidophilia properties for active crystallin synthesis and accumulation (McDevitt & Brahma, 1973;Brahma & McDevitt, 1974). Taking into account that under the present experimental conditions, increase of ribosomal population was never observed, also a control on the expression of the ribosomal genes cannot be excluded.…”

“…The studies on lens-transdifferentiation of the corneal cells (Brahma & McDevitt, 1974;Bosco & Filoni, 1992;Bosco et al, 1993b) show that during this process the crystallins are actively synthesized and accumulated into lens fibres. It is likely that the control at the transcriptional level, evidenced in this paper, can be exerted on the enhancement rather than on the crystallin gene^ expression.…”

“…An in vitro experimental analysis of the lens-transdifferentiation of X. laevis outer cornea has recently evidenced that this process is dependent on the presence of the neural retina, not only for its start but also for the completion of the lens-transdifferentiation of the outer cornea (Bosco et al, 1993b(Bosco et al, , 1997. The epithelial corneal cells can transdifferentiate into lens fibres also when these cells are cultured in the presence of neural retina conditioned medium (Bosco et al, in press).…”