THE INHIBITION OF CELL-PROLIFERATION BY MITOMYCIN-C DOES NOT PREVENT TRANSDIFFERENTIATION OF OUTER CORNEA INTO LENS IN LARVAL XENOPUS-LAEVIS

The aim of the present work is to evaluate the relationship between ce ll proliferation and transdifferentiation (TS) of the outer cornea int o lens in larval Xenopus laevis. Data obtained from corneal fragments treated with Mitomycin C (MMC) (0.1 mg/ml, 50 min) and implanted into the vitreous chamber (MMC/v ch) were compared with those obtained from untreated corneal fragments implanted into the vitreous chamber (cont r/v ch) or between outer and inner corneas (contr/o c). Results demons trated that in contr/v ch implants, which transdifferentiated into len ses or lentoid bodies in 88% of cases, the mitotic index (MI) showed a sharp increase during the period of lens vesicle formation (3 days) a nd became very low when the formation of lens fibres was under way (7 days). In contro c implants, which did not undergo any lens forming tr ansformations, the MI remained unchanged in comparison to time O. In M MC/v ch implants, the inhibition of the mitotic activity was 100% up t o the third day after implantation. On the fifth and seventh days, sca nt mitotic activity was observed in some cases, but the MI was much lo wer than the MI of contr/o c implants. The MMC/v ch implants transdiff erentiated into lentoid bodies in 26% of cases. The lentoid bodies wer e much smaller than those observed in control implants, but they react ed positively with the lens antibodies at the same time after implanta tion as controls. Even the complete inhibition of proliferation due to stronger MMC treatments (e.g. 0.15 mg/ml, 50 min) did not prevent len s TS. On the whole, these data indicate that in larval Xenopus laevis the retinal factor present in the vitreous chamber, besides promoting cell proliferation in the outer cornea, also has an instructive action in specifying the lens phenotype. An increased proliferation may be f avourable for lens TS of cornea but is not a prerequisite for it.