Src42A is required for E-cadherin dynamics at cell junctions during Drosophila axis elongation.

Src kinases are important regulators of cell adhesion. Here we explored the function of Src42A in junction remodelling during Drosophila gastrulation. Src42A is required for tyrosine phosphorylation at bicellular (bAJ) and tricellular junctions (tAJ) in germband cells and localizes to hotspots of mechanical tension. The role of Src42A was investigated using maternal RNAi and CRISPR-Cas9-induced germline mosaics. We find that during cell intercalations, Src42A is required for the contraction of junctions at anterior-posterior cell interfaces. The planar polarity of E-cadherin is compromised and E-cadherin accumulates at tricellular junctions after Src42A knock down. Furthermore, we show that Src42A acts in concert with Abl kinase, which has also been implicated in cell intercalations. Our data suggest that Src42A is involved in two related processes; in addition to establishing tension generated by the planar polarity of MyoII, it may also act as a signalling factor at tAJs in controlling E-cadherin residence time.