Distinct embryotoxic effects of lithium appeared in a new assessment model of the sea urchin: the whole embryo assay and the blastomere culture assay.

Early embryogenesis is one of the most sensitive and critical stages in animal development. Here we propose a new assessment model on the effect of pollutant to multicellular organism development. That is a comparison between the whole embryo assay and the blastomere culture assay. We examined the LiCl effect on the sea urchin early development in both of whole embryos and the culture of isolated blastomeres. The mesoderm and endoderm region were capable to differentiate into skeletogenic cells when they were isolated at 60-cell stage and cultured in vitro. The embryo developed to exogastrula by the vegetalizing effect of the same LiCl condition where ectodermal region changed their fate to endoderm, while the isolated blastomeres from the presumptive ectoderm region differentiated into skeletogenic cells in the culture with LiCl. The effect of LiCl to the sea urchin embryo and to the dissociated blastomere is a unique example where same cells response distinctly to the same agent depend on the condition around them. Present results show the importance of examining the process in cellular and tissue levels for the exact understanding on the morphological effect of chemicals and metals.

Exogastrulation and interference with the expression of major yolk protein by estrogens administered to sea urchins.

Although estrogens have been detected in some echinoderm species, their role is not clearly understood; so we examined the effects of estrogens administered to sea urchin embryos and larvae. A typical malformation was exogastrulation, induced by the exposure to ethynylestradiol (EER) in a defined period of 12 h from 12 h after fertilization (HAF). Morphogenesis for gastrulation was delayed in the treated embryos: protrusion of the archenteron started at 30 HAF when gastrulation had already finished in normal embryos. Exogastrulation induced by EER was cancelled by the antiestrogen chemical, ICI182,780. Feeding larvae were less sensitive to estrogens than those in early embryogenesis and, at certain concentrations, developed without abnormal morphology. The effect of estrogens was examined at the level of gene expression of the major yolk protein (MYP). MYP expression started during the larval stage and was suppressed by estrone at the six-armed stage, but not by beta-estradiol, and in later stage larvae, the expression was not affected by treatment with either estrogen. Estrogens affect sea urchins in the early stage of embryogenesis, leading to abnormal morphogenesis and interference with gene expression.