The brinker gradient controls wing growth in Drosophila

The Decapentaplegic (Dpp) morphogen gradient controls growth and patterning in the Drosophila appendages. There is recent evidence indicating that the Dpp gradient is converted into an inverse gradient of activity of the gene brinker (brk), which encodes a transcriptional repressor and is negatively regulated by the Dpp pathway. We have studied how alterations in the Brk gradient affect the growth of the wing disc. We find that there is a negative correlation between brk activity and growth of the disc: high levels of brk prevent or reduce growth, whereas loss of brk activity results in excessive growth. This effect is concentration dependent: different amounts of Brk produce distinct rates of growth. Furthermore, our results demonstrate that although brk is able to induce apoptosis where there is a sharp difference in Brk levels, its role as a growth repressor is not achieved by inducing apoptosis but by reducing cell proliferation. Brk appears to downregulate the activity of genes that control cell proliferation, such as bantam.