Cytocortex-dependent dynamics of Drosophila Crumbs controls junctional stability and tension during germ band retraction

Abstract

During morphogenesis, epithelia undergo dynamic rearrangements, which requires continuous remodelling of junctions and cell shape, but at the same time mechanisms preserving cell polarity and tissue integrity. Apico-basal polarity is key for the localisation of the machinery that enables cell shape changes. The evolutionarily conserved Drosophila Crumbs protein is critical for maintaining apico-basal polarity and epithelial integrity. How Crumbs is maintained in a dynamically developing embryo remains largely unknown. Here, we applied quantitative fluorescence techniques to show that, during germ band retraction, Crumbs dynamics correlates with the morphogenetic activity of the epithelium. Genetic and pharmacological perturbations revealed that the mobile pool of Crumbs is fine-tuned by the actomyosin cortex in a stage-dependent manner. Stabilisation of Crumbs at the plasma membrane depends on a proper link to the actomyosin cortex via an intact FERM-domainbinding site in its intracellular domain, loss of which leads to increased junctional tension and higher DE-cadherin (also known as Shotgun) turnover, resulting in impaired junctional rearrangements. These data define Crumbs as a mediator between polarity and junctional regulation to orchestrate epithelial remodelling in response to changes in actomyosin activity. This article has an associated First Person interview with the first author of the paper.

Tissue-wide coordination of epithelium-to-neural stem cell transition in the Drosophila optic lobe requires Neuralized

“…For instance, E-cad could be internalized at a faster rate in the absence of the Crb complex in epi-NSCs. This working hypothesis is consistent with the notion that the Crb complex stabilizes AJs and regulates MyoII at junctions to maintain epithelium integrity during morphogenesis (Harris and Tepass, 2008;Flores-Benitez and Knust, 2015;Campbell et al, 2009;Bajur et al, 2019;Perez-Mockus et al, 2017b;Röper, 2012;Salis et al, 2017;Sen et al, 2012). It is also consistent with our observation that loss of Crb regulation by Neur led to E-cad persisting in NSCs past the TZ.…”

“…Sdt interacts with Pals1-associated tight junction (Patj) to form a Crb-Sdt-Patj complex (Bulgakova and Knust, 2009). The apical Crb complex is required to stabilize adherens junctions (AJs) and maintain epithelial integrity during tissue remodeling in Drosophila (Harris and Tepass, 2008;Bajur et al, 2019;Flores-Benitez and Knust, 2015;Campbell et al, 2009;Perez-Mockus et al, 2017b;Röper, 2012;Salis et al, 2017). Recently, the conserved E3 ubiquitin ligase Neuralized (Neur) was found to interact with specific isoforms of Sdt, and this interaction appeared to target the Crb complex proteins for endocytosis and degradation (Chanet and Schweisguth, 2012;Perez-Mockus et al, 2017b).…”

Crumbs organizes the transport machinery by regulating apical levels of PI(4,5)P2 in Drosophila

“…Moreover, by using dominant active or inactive forms of Rab5 (Zhang et al, 2007), we obtained inconsistent results (data not shown), probably due to pleiotropic effects of these versions of Rab5, which tend to titer effectors shared with other Rab proteins (Pylypenko et al, 2017; Müller and Goody, 2018). Although loss of β H -Spec function has been linked to increased endocytosis in some Drosophila epithelia (Williams et al, 2004; Pellikka et al, 2002; Richard et al, 2009; Phillips and Thomas, 2006), or Crb mobility in the embryonic epidermis (Bajur et al, 2019) data presented here support the conclusion that in larval SGs Crb predominantly regulates apical membrane traffic and secretion, though we cannot completely rule out a minor contribution of endocytosis to the phenotypes observed.…”

Neuralized regulates a travelling wave of Epithelium-to-Neural Stem Cell morphogenesis inDrosophila

“…While it is not known whether the kinetics of E-cad endocytosis vary between NE and epi-NSCs, we note that this view is entirely consistent with the notion that Crb stabilizes AJs and is required to maintain epithelium integrity in contexts of morphogenesis, e.g. cell delamination, cell-cell intercalation and division (Harris and Tepass, 2008;Bajur et al, 2019;Flores-Benitez and Knust, 2015;Campbell et al, 2009;Perez-Mockus et al, 2017b;Röper, 2012;Salis et al, 2017). Future studies will address whether Neur promotes a faster turn-over of E-cad via its regulatory activity on the Crb complex and/or cortical actomyosin.…”

“…These NSCs give rise to the medulla neurons that will comprise part of the visual processing center of the adult brain. This proneural wave is proposed to travel through the NE via an required to stabilize AJs and maintain epithelial integrity during tissue remodeling in Drosophila (Harris and Tepass, 2008;Bajur et al, 2019;Flores-Benitez and Knust, 2015;Campbell et al, 2009;Perez-Mockus et al, 2017b;Röper, 2012;Salis et al, 2017). Recently, the conserved E3 ubiquitin ligase Neuralized (Neur) was found to directly interact with specific isoforms of Sdt and this interaction appeared to target Crb for endocytosis and degradation (Perez-Mockus et al, 2017b).…”