Local overexpression of Su(H)-MAPK variants affects Notch target gene expression and adult phenotypes in Drosophila

摘要

In Drosophila , Notch and EGFR signalling pathways are closely intertwined. Their relationship is mostly antagonistic, and may in part be based on the phosphorylation of the Notch signal transducer Suppressor of Hairless [Su(H)] by MAPK. Su(H) is a transcription factor that together with several cofactors regulates the expression of Notch target genes. Here we address the consequences of a local induction of three Su ( H ) variants on Notch target gene expression. To this end, wild-type Su ( H ), a phospho-deficient Su ( H ) MAPK- ko and a phospho-mimetic Su ( H ) MAPK-ac isoform were overexpressed in the central domain of the wing anlagen. The expression of the Notch target genes cut, wingless, E ( spl ) m8-HLH and vestigial , was monitored. For the latter two, reporter genes were used ( E ( spl ) m8-lacZ, vg BE -lacZ ). In general, Su ( H ) MAPK- ko induced a stronger response than wild-type Su ( H ), whereas the response to Su ( H ) MAPK-ac was very weak. Notch target genes cut, wingless and vg BE -lacZ were ectopically activated, whereas E ( spl ) m8-lacZ was repressed by overexpression of Su(H) proteins. In addition, in epistasis experiments an activated form of the EGF-receptor ( DER act ) or the MAPK ( rl SEM ) and individual Su(H) variants were co-overexpressed locally, to compare the resultant phenotypes in adult flies (thorax, wings and eyes) as well as to assay the response of the Notch target gene cut in cell clones.