Xenopus laevis embryo development: Arrest of epidermal cell differentiation by the chelating agent 1,10-phenanthroline

The embryonic epidermis of stage 35 Xenopus laevis embryos is a highly diff erentiated structure composed of four cell types arranged in a regular arch itecture. Each type is distinguished by its distinct morphological characte ristics. Some cells are ciliated (type 1); others have their surfaces cover ed by abundant, secreted Vesicles of 0.1 mu m diameter (type 2), or multipl e linear aggregates of spherical subunits on their apical surfaces (type 3) or large secreted vesicles that emanate from prominent apical holes of 1 m u m diameter (type 4). In contrast, the macroscopic appearance of embryos e xposed to 10 mu M 1,10-phenanthroline (OP) as well as the ultramicroscopic structure and organization of their epidermal cells are markedly altered. T he most predominant cells of the embryonic epidermis are undifferentiated a nd of heterogeneous size. They lack any characteristic morphology and are a rranged irregularly. Ghost cells are also identified. The recognizable diff erentiated cells are decreased in number and present in a scattered arrange ment. These are identified as either type 1 or 2 cells but with ciliae that are shorter and thicker than control or with only a few Vesicles larger th an 0.1 mu m in diameter on their surface. No cells with linear aggregates o r prominent apical holes are identified. Except for the altered epidermis, the embryos do not develop any other major organs and exhibit axial abnorma lities with an average dorso-anterior index of three. Thus, the chelating a gent OP perturbs metal dependent processes essential for terminal different iation that may likely account for the resultant abnormalities of embryo or ganogenesis and morphogenesis. (C) 2000 Wiley-Liss, Inc.