Actin-dependent membrane polarization reveals the mechanical nature of the neuroblast polarity cycle

Abstract

Highlights d Drosophila neural stem cell membranes are heterogenous d Membrane features become polarized during asymmetric division d Membrane and protein polarity cycles are precisely synchronized d Actin-dependent forces deform the surrounding tissue during the polarity cycle

Phases of cortical actomyosin dynamics coupled to the neuroblast polarity cycle

“…While both LatA and CytoD inhibited aPKC coalescence into an apical cap, we noticed that aPKC was maintained in the apical hemisphere for a longer period in CytoD-treated neuroblasts ( Figure 3B–D , Figure 3—video 3 , Figure 3—video 4 , and neuroblasts used for measurements in Figure 3—video 5 ). Some localized enrichments remained in the apical hemisphere in neuroblasts treated with either drug, possibly due to their association with localized membrane enrichments, as recently reported ( LaFoya and Prehoda, 2021 ). However, aPKC signal entered the basal hemisphere more rapidly in LatA- versus CytoD-treated neuroblasts ( Figure 3D ).…”

“…The cycle of cortical actomyosin dynamics is completed when the movement abruptly changes direction at anaphase leading to the cleavage furrow-directed flows that have been previously characterized ( Barros et al, 2003 ; Roubinet et al, 2017 ). While we have examined the relationship between actomyosin dynamics and cortical protein polarity, we note that a neuroblast membrane polarity cycle was recently discovered and found to require the actin cytoskeleton ( LaFoya and Prehoda, 2021 ). The mechanical phases of the membrane polarity cycle may be related to the phases of cortical actomyosin dynamics we report here.…”

“…The current model for neuroblast actomyosin dynamics is primarily based on the analysis of fixed cells or by imaging a small number of medial sections in live imaging experiments and we recently found that rapid imaging of the full neuroblast volume can reveal dynamic phases of movement that are not detected with other methods ( LaFoya and Prehoda, 2021 ; Oon and Prehoda, 2019 ). Here, we use rapid full volume imaging to investigate whether cortical actomyosin dynamics are present in neuroblasts when the Par complex undergoes its polarity cycle.…”

Phases of cortical actomyosin dynamics coupled to the neuroblast polarity cycle

“…Here we find that when cortical actin is depolymerized during interphase (Figure 3A,A’ and Figure 3-video 1), aPKC is recruited to the apical cortex, but fails to undergo apically-directed movements and spreads prematurely to the basal pole (n = 36/36 neuroblasts from 15 larvae). Localized enrichments of aPKC have been reported at plasma membrane domains (LaFoya and Prehoda, 2021), and these domains normally move towards the apical pole shortly before metaphase. Consistent with previous observations (LaFoya and Prehoda, 2021), we find that these aPKC enrichments stop movement once cortical actin is depolymerized.…”

“…Localized enrichments of aPKC have been reported at plasma membrane domains (LaFoya and Prehoda, 2021), and these domains normally move towards the apical pole shortly before metaphase. Consistent with previous observations (LaFoya and Prehoda, 2021), we find that these aPKC enrichments stop movement once cortical actin is depolymerized. Thus, cortical actin and aPKC dynamics are highly correlated during mitosis, and aPKC coalescence into an apical cap ceases immediately following the loss of cortical actin.…”