Lara Salvany, Julius Muller, Ernesto Guccione, and Pernille Rørth
Published in Genes & Development on 15 May 2014.
The transcription cofactor MAL is regulated by free actin levels and thus by actin dynamics. MAL, together with its DNA-binding partner, SRF, is required for invasive cell migration and in experimental metastasis. Although MAL/SRF has many targets, we provide genetic evidence in both Drosophila and human cellular models that actin is the key target that must be regulated by MAL/SRF for invasive cell migration. By regulating MAL/SRF activity, actin protein feeds back on production of actin mRNA to ensure sufficient supply of actin. This constitutes a dedicated homeostatic feedback system that provides a foundation for cellular actin dynamics.
Figure Legend: Transposon mutagenesis induces medulloblastoma.
Identification of direct target genes for mal-d in Drosophila. (A) Stage 10 egg chamber from a mal-dD7 homozygous female. The border cell cluster is labeled by GFP and indicated by a green arrow. Anterior is to the left in this and all other images. Border cells normally migrate from the anterior end and to the oocyte (white asterisk in A and C) by stage 10 (as in C), so migration here is severely defective. DAPI (nuclei) is
in gray, and phalloidin (F-actin) is in red. (B) Ovary from a mal-dD7 homozygous female stained with DAPI (gray) and phalloidin (red). (C) Stage 10 egg chamber and ovary (shown in D) from tub mal-d3xGFP; mal-dD7 homozygous females. Ubiquitous expression of mal d3xGFP rescues border cell migration (green arrow) and ovary defects (stained as in A and B). (E) Diagram of strategy to identify direct targets of mal-d. ChIP on tub mald3xGFP; mal-dD7 ovaries identified 168 enriched peaks. Expression profiling of ovaries identified 98 genes with a significant decrease in expression in mal-dD7 homozygous females compared with wild type (OR+). The overlap is the six listed genes. (F, top) Binding profile of Mal-d-GFP to the Actin5C genomic region (blue) represented by score (number of reads per peak). Actin5C mRNA and ORF are indicated below (red). Peaks 2 and 3 (and peak 4) are in the promoter region, and peak 1 is 10 kb upstream. (Below) Aligned genomic regions from other Drosophilids(Drosophila simulans and Drosphila pseudoobscura) (same scale; data from FlyBase). The actin genes are highly conserved, the overall locus organization is similar, and the upstream peak 1 is conserved (blue boxes).
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