The promoter from the metallothionein gene may be a useful conditional promoter for the construction of chimeric genes to be expressed in Drosophila cells in culture. To explore this possibility the responses of the endogenous metallothionein gene and an in vitro constructed chimeric gene containing the metallothionein promoter were examined. Copper and cadmium, when added to the growth medium of Drosophila Schneider's line 2 cells, can produce a 30-100 fold induction of metallothionein mRNA levels. The level of induction depends on the amount of copper or cadmium added to the medium and these mRNA levels remain high for at least four days. Copper is less toxic than cadmium and does not induce a typical heat-shock response in the cells. Finally, a chimeric gene containing the metallothionein promoter shows a similar induction when transformed into the cells.

Wnt and Hedgehog signaling pathways play central roles in embryogenesis, stem cell maintenance, and tumorigenesis. However, the mechanisms by which these two pathways interact are not well understood. Here, we identified a novel mechanism by which Wnt signaling pathway stimulates the transcriptional output of Hedgehog signaling. Wnt/β-catenin signaling induces expression of an RNA-binding protein, CRD-BP, which in turn binds and stabilizes GLI1 mRNA, causing an elevation of GLI1 expression and transcriptional activity. The newly described mode of regulation of GLI1 seems to be important to several functions of Wnt, including survival and proliferation of colorectal cancer cells. [Cancer Res 2009;69(22):8572-8]

Wnt growth factors acting through the canonical intracellular signaling cascade play fundamental roles during vertebrate brain development. In particular, canonical Wnt signaling is crucial for normal development of the dorsal midbrain, the future optic tectum. Wnts act both as patterning signals and as regulators of cell growth. In the developing tectum, Wnt signaling is mitogenic; however, the mechanism of Wnt function is not known. As a step towards better understanding this mechanism, we have identified two new Wnt targets, the closely linked zic2a and zic5 genes. Using a combination of in vivo assays, we show that zic2a and zic5 transcription is activated by Tcf/Lef transcription factors in the dorsal midbrain. Zic2a and Zic5, in turn, have essential, cooperative roles in promoting cell proliferation in the tectum, but lack obvious patterning functions. Collectively these findings suggest that Wnts control midbrain proliferation, at least in part, through regulation of two novel target genes, the zic2a-zic5 gene pair.

Anteroposterior (A/P) patterning of the vertebrate neurectoderm begins early during development. In vitro explant assays have been used to show that an A/P subdivision of the zebrafish neurectoderm is in place by early gastrulation. However, no direct markers of this subdivision had been described. We report isolation of two members of the zic gene family, zic2 and zic3, which mark distinct regions in the developing nervous system. zic3 is expressed in early gastrula embryos in a posterior domain, directly demonstrating that A/P pattern is present in the future neurectoderm by this stage. Analysis of mutants in genes encoding bone morphogenetic proteins (BMPs) shows that dorsal restriction of zic3 expression requires intact BMP function, and that posterior restriction of zic3 expression is regulated independently of BMP signaling. These data show an early subdivision of the A/P axis in the presumptive neurectoderm.