The correlation between patterns of dye transfer through gap junctions and future developmental fate in Xenopus: the consequences of u.v. irradiation and lithium treatment

Abstract

ABSTRACT The correlation between cell-to-cell communication through gap junctions at the 32-cell stage and the subsequent patterning of the embryonic axis has been examined in Xenopus laevis embryos. Disturbances of embryonic axis formation were generated by exposure to u.v. irradiation at the vegetal pole before 0·6 in the cell cycle, which generates embryos with dorsal axial deficiencies. Alternatively embryos were treated with 100 mm-lithium chloride between the 2-cell and 32-cell stage, which generates embryos with ventral axial deficiencies. The cell-to-cell transfer of Lucifer Yellow was used to monitor junctional permeability. Injections were made into animal hemisphere cells, lying in tiers 1 and 2 of the 32-cell embryo, whose position relative to the future dorsoventral axis of the embryo was determined on the basis of differences in pigmentation. The frequency of Lucifer Yellow transfer in the future dorsal half of the animal hemisphere was compared with that in the future ventral half for control (untreated), u.v.-irradiated and Li-treated embryos. Injected embryos were subsequently scored for axial development for comparison with dye transfer frequencies. In control embryos at the 32-cell stage, Lucifer Yellow transfer was both more frequent and more extensive in future dorsal regions than in future ventral regions, as observed previously. In embryos that had been u.v. irradiated before 0·6 in the first cell cycle, Lucifer transfer was the same in both light and dark regions of the animal hemisphere and at the low level characteristic of future ventral regions in normal embryos. These embryos developed with massive reductions in dorsal axial structures. Embryos irradiated after 0-8 in the first cell cycle, when u.v. irradiation no longer inhibits the cytoplasmic movements initiated at fertilization, showed a normal dorsoventral difference in Lucifer Yellow transfer and developed with normal dorsoventral polarity. Embryos exposed to 100mm-LiCl contained 1·4 mm-lithium at the end of the treatment period. The transfer of Lucifer Yellow between animal pole cells of 32-cell embryos previously treated with LiCl was the same in both light (dorsal) and dark (ventral) and at the high level characteristic of future dorsal regions in normal embryos. Such embryos subsequently developed with substantial ventral axis deficiencies. U.v.-irradiated embryos subsequently treated with lithium showed transfer rates in ventral regions equivalent to that in embryos treated with Li alone and developed with ventral axial deficiencies. We conclude that the frequency with which Lucifer Yellow transfers through gap junctions at the 32-cell stage indicates the future developmental fate of animal cells and can be used to predict the subsequent organization of the embryonic axis.