Rab11 plays a key role in stellate cell differentiation via non-canonical Notch pathway in Malpighian tubules of Drosophila melanogaster

Rab11, a member of Rab-GTPase family, and a marker of recycling endosomes has been reported to be involved in the differentiation of various tissues in Drosophila. Here we report a novel role of Rab11 in the differentiation of stellate cells via the non-canonical Notch pathway in Malpighian tubules. During Malpighian tubule development caudal visceral mesodermal cells intercalate into the epithelial tubule of ectodermal origin consisting of principal cells, undergo mesenchymal to epithelial transition and differentiate into star shaped stellate cells in adult Malpighian tubule. Two transcription factors, Teashirt and Cut (antagonistic to each other) are known to be expressed in stellate cells and principal cells, respectively, from early stages of development and serve as markers for these cells. Inhibition of Rab11 function or over-expression of activated Notch in stellate cells resulted in the expression of Cut that leads to down-regulation of Teashirt or vice-versa that leads to hampered differentiation of stellate cells. The stellate cells do not transform to star/bar shaped and remain in mesenchymal state in adult Malpighian tubule. Over-expression of Deltex, which plays important role in non-canonical Notch signaling pathway, shows similar phenotype of stellate cells as seen in individuals with down-regulated Rab11, while downregulation of Deltex in genetic background of Rab11(RNAi) rescues Teashirt expression and shape of stellate cells. Our experiments suggest that an inhibition or reduction of Rab11 function in stellate cells results in the faulty recycling of Notch receptors to plasma membrane as they accumulate in early and late endosomes, leading to Deltex mediated non-canonical Notch activation.