ZN2-INDUCTION OF METALLOTHIONEIN IN MYOTOMAL CELL-NUCLEI DURING SOMITOGENESIS OF XENOPUS-LAEVIS()

The localization of metallothionein in control and Zn-exposed embryos of Xenopus laevis was studied by whole-mount immunohistochemical stain ing. The embryos were grown according to the FETAX (Frog Embryo Terato genesis Assay: Xenopus) protocol from N/F stage 8 to stage 47, with or without addition of ZnCl2 (300 mu M) to the medium. At stages 27, 38, 42, 45, and 47, control and Zn-exposed embryos were fixed in buffered formalin, and whole mounts were stained by an immunoperoxidase techni que, using monoclonal murine antibody to equine metallothionein. Stain ing of metallothionein was evident in myotomal cell nuclei of developi ng somites by stage 27, stomatodeum, oropharynx, and gills by stage 38 , developing kidneys (mesonephros) by stage 45, and liver by stage 47. The staining of metallothionein at these sites was more intense in Zn -exposed embryos than controls. The central nervous system (especially the spinal cord) and the yolk mass were faintly stained for metalloth ionein in controls and Zn-exposed embryos. Staining of metallothionein in myotomal cell nuclei was most prominent at stage 38, diminished at stages 42 and 45, and practically disappeared by stage 47. This is th e first report that metallothionein is expressed in myotomal cell nucl ei of Xenopus embryos during normal somitogenesis and becomes increase d when the embryos are exposed to teratogenic levels of Zn2+. (C) 1996 Wiley-Liss, Inc.