Genetic screen for regulators of ind expression identifies shrew as encoding a novel twisted gastrulation-like protein involved in Dpp signaling.

Initiation and refinement of expression of the Ind homeodomain protein in the Drosophila embryo is coordinately regulated by global dorsoventral patterning pathways Dorsal, Egfr, and Dpp, and well as by Vnd, which positions the ventral boundary of Ind. Therefore, we set out to look for novel regulators of dorsoventral patterning by screening the Exelixis deficiency collection for modified expression of Ind. Indeed, we found deficiencies that remove components of the known signaling pathways had altered or lost ind expression.

Identification of an upstream regulatory element reveals a novel requirement for Ind activity in maintaining ind expression.

A maternally established gradient of nuclear Dorsal protein is the first step in subdivision of the Drosophila neurectoderm into stripes of homeodomain gene expression. Dorsal in combination with the EGF and TGFbeta signaling pathways are key regulators of the expression of the genes ventral nervous system defective (vnd), intermediate neuroblasts defective (ind), and muscle segment homeobox (msh) in the developing neurectoderm. These three genes encode homeodomain transcription factors that can repress each other, which ensures adjacent, non-overlapping expression domains.