Functional Analysis of Src42A in embryonic epithelial morphogenesis of Drosophila melanogaster

Src42A is one of the Src family kinases (SFKs) present in Drosophila melanogaster. In mammals there are 8 SFKs and so far, a loss of function analysis of SFKs were difficult to conduct due to their functional redundancy. In Drosophila, there are only two SFKs namely Src42A and Src64B, the former is essential for embryonic development and the latter is a non-essential gene. Since Src42A is supplied as a maternal component, the zygotic mutant were showing defects in later developmental stages, because the contribution of maternal Src42A is stronger in early stages of development. Depleting maternal Src42A was challenging because of its genomic locus. To understand the function of Src42A during early developmental stages, loss of function analyses were performed using RNAi and CRISPR/Cas9 methods. Upon depletion of maternal Src42A, the early developmental stages including cellularization and germband elongation processes were affected. I explored the function of Src42A in adherens junction remodelling during Drosophila germband elongation. Src42A localizes at the hotspots of mechanical tension and is required for tyrosine phosphorylation at bicellular (bAJ) and tricellular junctions (tAJ) in germband cells. I found that during cell intercalations, Src42A is required for the contraction of AP cell junctions and the AP cell junction of intercalating cells displayed less tension. In addition, the planar cell polarity of E-cadherin and β-catenin is compromised, and E-cadherin accumulates at tricellular junctions after Src42A knock down. Furthermore, Src42A acts upstream of Abl and together they control the speed of germband elongation. 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. In this thesis I have also reported preliminary findings on the impact of Src42A in cellular arrangement during cellularization. The experimental results include the impact of Src42A kinase in regulating AJ formation, by clustering Bazooka protein which is core of adherens junction.