Temporal and spatial manipulation of gene expression in Xenopus embryos by injection of heat shock promoter-containing plasmids.

The temporal and spatial manipulation of gene expression is useful in analyzing the mechanisms of early embryogenesis. This report describes a modified strategy to achieve controlled gene expression by directed plasmid injection using the hsp70 promoter and heat treatment. Two control genes, enhanced green fluorescent protein (EGFP) and beta-catenin, were also expressed by this method. When embryos were injected with HsS1/EGFP and subsequently heat-treated, ectopic EGFP was expressed only in the injected area. No severe defects were attributable to the heat treatment alone. Western blotting confirmed that no EGFP induction occurred in the absence of heat treatment and that, in the presence of heat induction, EGFP expression was detected within 1 hr after treatment. These results suggest that heat-mediated gene expression in the restricted area was regulated temporally. In addition, HsS1/beta-catenin injection into the animal pole of 8-cell embryos, followed by heat treatment, caused loss of head formation that was similar to that seen with CS2/beta-catenin injection. Although a hormone-inducible gene induction system already exists in Xenopus, our modified technique provides an alternative method for controlling temporal and spatial gene expression.