Roles of Mind bomb 2, microRNAs and tissue architecture in the regulation of collective cell migration in Drosophila

Abstract

Cell migration is essential in animal development and co-opted during metastasis and inflammatory diseases. Some cells migrate as a collective, which requires them to maintain epithelial characteristics, such as stable cell-cell adhesions, while adopting motile characteristics, such as rapid turnover of adhesions and dynamic cytoskeletal structures. How this regulation is unclear but important to study. We examined this issue at the levels of protein regulation, gene regulation, and physical regulation. While investigating Drosophila oogenesis, we found that the putative E3 ubiquitin ligase, Mind bomb 2 (Mib2), is required to promote epithelial stability as well as the collective cell migration of border cells. mib2 mutant follicle cells have drastically reduced E-cadherin-based adhesion complexes and lower levels of actin filaments. Through mass spectroscopy and biochemical analysis, we identified components of Mib2 complexes, which include E-cadherin and ?- and ?-catenins, as well as actin regulators. We also found new roles for three Mib2 interacting proteins, RhoGAP19D, Supervillin, and Modulo, in border cell migration. We conclude that Mib2 acts to stabilize E-cadherin-based adhesion complexes and promote a robust actin cytoskeletal network, which is important both for epithelial integrity and collective cell migration. In addition to protein regulators, the Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) pathway is required during border cell migration to modulate gene expression. To get a deeper understanding of JAK/STAT signaling regulation, we examined candidate microRNAs. We focused on microRNAs predicted to regulate or be regulated by STAT signaling components such as Apontic and Slow border cells. Our analysis suggests that miR-8, miR-279, mir-315, and let-7 may act within a JAK/STAT signaling feedback loop to influence collective cell migration. In the third type of regulation, prior work suggests that the JAK/STAT activator Unpaired (Upd) asymmetrically signals in egg chambers owing to the tissue architecture. Here, we developed a new tool to assay the distribution of Upd in extracellular regions of egg chambers. This will be used to study how the contours of surrounding cells affect the JAK/STAT activation pattern in follicle cells. In our work, we identified several regulators of cytoskeletal meshwork and JAK/STAT signaling that are crucial in oogenesis and provide avenues for further research. Both collective cell migration and JAK/STAT signaling are involved in autoimmune disorders and metastatic cancer progression, so our results may apply to other contexts.