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		Ultraviolet irradiation impairs epiboly via microtubules in Zebrafish embryos Didier Alcaraz,Developmental Biology, Franklin and Marshall College, Lancaster, PA Introduction Zebrafish have transparentembryos that develop outside the mother. They develop rapidly, so that at 24 hours after fertilization, the embryo has formed most of its tissue and organ primordia and displays the characteristic tadpole-like form. Also, the cell division occur only in the animal pole blastodisc. These divisions are rapid, with a periodicity of about 15 minutes each. The first 12 divisions occur synchronously, forming a mound of cells that sits at the animal pole of a large yolk cell. Three kind of movements (epiboly, involution and convergence) can be distinguished in the early development of zebrafish embryo. Involution and convergence result of migration of deep cells moving presumably using fibroblasts, but the molecular nature of the mechanism driving the epiboly is not known yet. Previous experiments showed that irradiation of zebrafish zygotes with ultraviolet light selectively impairs epiboly resulting in embryos with open blastopores but well-formed anterior axes. The ultraviolet light effect is not restricted to the zygote stage as irradiation of later embryonic stages also impairs epiboly. The ultraviolet-sensitive target may thus be maternally encoded components of the machinery driving epiboly. Reference: U. Strahle and S. Jesuthasan, Development 119, 909-919 (1993) Objective The objective of this experiment was to expose several embryos at different level of UV irradiation and observe the potential malformations .