The Bi-functional Role of BMP in mid Regulation in Drosophila

Abstract

During early embryogenesis, intracellular signals determine whether follicle cells differentiate towards  anterior or posterior fate. Bone Morphogenetic Protein (BMP) is one of the regulatory proteins repressing mid, a transcription factor that induces the posterior pattern formation in Drosophila. BMP regulates mid expression by binding to the intron segment of the mid gene, known as mid-in. Previous work using the lacZ reporter in mid-in has shown that  mid-,requires BMP expression in some cases, presenting a potential bi-functional role of BMP. We hypothesize that such a property might be determined by the availability of schnurri, a well-known co-repressor of BMP. We examined lacZ fused with mid-in in three groups of Drosophila, over expression of BMP, knock-down of schnurri, and the combination of both genotypes. Each group contained 40 samples  and was analyzed using genetic mosaic analysis.  We found that reporter expression decreased substantially when schnurri was present and BMP was over expressed. In contrast,  the reporter was ectopically expressed when schnurri was absent and BMP signalling was overactivated. However, because schnurri was only knocked down using schnurri RNAi in this experiment, the activation phenotype was not strong. Future experiments could repeat this analysis using Drosophila with a schnurri gene mutation instead. Overall, these results demonstrate the bifunctional property of BMP pathway in the regulation of the mid-in reporter. Future work may focus on identifying the locations of the BMP activation and repression motif within the mid-in sequence.