A Non-Canonical Raf Function Is Required for Dorsal-Ventral Patterning in Drosophila Embryogenesis

Embryonic development requires the establishment of directional axes. In Drosophila, spatially discrete expression of transcription factors determines the anterior to posterior organization of the early embryo, while the Toll and TGF-beta signalling pathways determine the early dorsal to ventral pattern. Embryonic MAPK/ERK signaling contributes to both anterior to posterior patterning in the terminal regions and to dorsal to ventral patterning during oogenesis and embryonic stages. Here we describe a novel loss of function mutation in the Raf kinase gene, which leads to loss of ventral cell fates as seen through the loss of the ventral furrow, the absence of Dorsal/NF-kB nuclear localization, the absence of mesoderm determinants Twist and Snail, and the expansion of TGF-beta. Gene expression analysis showed cells adopting ectodermal fates similar to loss of Toll signaling. Our results combine novel mutants, live imaging, optogenetics and transcriptomics to establish a novel role for Raf, that appears to be independent of the MAPK cascade, in embryonic patterning. Overall design: Embryo RNA profiles of wild type (WT) and Raf926-/- Drosophila