Biochemical properties of abnormal embryos of echinoderms and amphibians

The role of Ca2+ in the regulation of embryogenesis in early amphibian and echinoderm embryos

It is difficult to measure intracellular calcium concentrations in dividing embryos and, furthermore, these interact with pHi and with cyclic nucleotides. Nevertheless, the evidence currently suggests that changing [Ca2+]i levels probably do not have a major role in controlling normal cell-to-cell communication and so do not integrate cell division during programmed cleavage in amphibian embryos. However, treatments that are known or expected to raise artificially cytoplasmic calcium to relatively high levels cause abnormal embryogenesis, probably via the uncoupling of intercellular communication of the blastomeres, and also cortical contractions in early echinoderm and amphibian embryos.

Electron microscope observations on preimplantation mouse embryos cultured with LiCl

We have recently shown that LiCl in the culture medium retards cleavage of mouse preimplantation embryos without delaying their blastulation and causes the formation of blastocysts with few large cells and a reduced or absent inner cell mass (Izquierdo and Becker 1982). In this study we compare the ultrastructure of major cellular organelles of Li+-treated and control embryos. No subcellular alterations were found that correlate with the altered morphology of the blastocysts. On the basis of these results we submit that the malformation of blastocysts developed in a Li+-containing medium is the morphogenetic consequence of a retardation of cleavage coupled with a normal timing in the establishment of zonular tight junctions around the peripheral cells of the morula.

A note on the mechanism of action of UV-irradiation of amphibian embryos

The actions on amphibian embryos of UV-irradiation, exposure to Li+ or exposure to ouabain show interesting parallels with their effects on spontaneous release at the presynaptic terminals of the neuromuscular junction. It is suggested that these treatments serve to raise intracellular Ca2+ ([Ca2+]i) in these examples, and that UV-promoted abnormalities in embryogenesis are a consequence of changes in [Ca2+]i at critical stages in development.