A novel mechanism of bulk cytoplasmic transport by cortical dynein in Drosophila ovary

Abstract

Cytoplasmic dynein, a major minus-end directed microtubule motor, plays essential roles in eukaryotic cells. Drosophila oocyte growth is mainly dependent on the contribution of cytoplasmic contents from the interconnected sister cells, nurse cells. We have previously shown that cytoplasmic dynein is required for Drosophila oocyte growth and assumed that it simply transports cargoes along microtubule tracks from nurse cells to the oocyte. Here we report that instead of transporting individual cargoes along stationary microtubules into the oocyte, cortical dynein actively moves microtubules within nurse cells and from nurse cells to the oocyte via the cytoplasmic bridges, the ring canals. This robust microtubule movement is sufficient to drag even inert cytoplasmic particles through the ring canals to the oocyte. Furthermore, replacing dynein with a minus-end directed plant kinesin linked to the actin cortex is sufficient for transporting organelles and cytoplasm to the oocyte and driving its growth. These experiments show that cortical dynein performs bulk cytoplasmic transport by gliding microtubules along the cell cortex and through the ring canals to the oocyte. We propose that the dynein-driven microtubule flow could serve as a novel mode of fast cytoplasmic transport.

Drosophilaoocyte specification is maintained by the dynamic duo of microtubule polymerase Mini spindles/XMAP215 and dynein

“…Characterizations of Orb concentration and Orb dispersion were previously described (27). For control samples: stage 5-6, 100% Orb concentrated and 0% Orb dispersed All samples with one copy of maternal αtub-Gal4 [V37] .…”

“…Young mated female adults of (1) yw; mat αtub-Gal4 [V37] /UASp-MoxMaple3-K10.TLS and (2) yw; mat αtub-Gal4 [V37] (F) Percentages of oocyte growth phenotypes in the listed genetic background (all with one copy of maternal αtub-Gal4 [V37] ). Classifications of oocyte growth phenotypes were previously described (27). For control samples: normal oocyte growth, 100%; delayed oocyte growth, 0%; partial small oocytes, 0%; complete small oocytes, 0% (N=72).…”

“…Dynein is not only required for oocyte specification but is also indispensable for maintaining oocyte differentiation. Later or weaker inhibition of dynein or its cofactors (such as Dhc64C, Dlic, p150/Glued, Lis1, Dlc, and Egl) results in gradual loss of oocyte identity (21,27), indicating that maintenance of the oocyte differentiation requires continuous dyneindriven activity. Intriguingly, dynein is not just working as a minus-end-directed motor along the pre-formed polarized microtubule network originating from the MTOC in the oocyte; rather, it is involved in organizing and maintaining this polarized network itself.…”

“…(G) Percentages of the Orb staining phenotypes in stage 5-6, stage 7-8, and stage 9 egg chambers in listed genotypes (all with one copy of maternal αtub-Gal4 [V37] ). Characterizations of Orb concentration and Orb dispersion were previously described (27). For control samples: stage 5-6, 100% Orb concentrated and 0% Orb dispersed (N=203); stage 7-8, 100% Orb concentrated and 0% Orb dispersed (N=91); stage 9, 100% Orb concentrated and 0% Orb dispersed (N=74).…”

Microtubules in Motion: dynamics and diversity of the microtubule cytoskeleton

“…Next, we aimed to identify the molecular motor proteins responsible for the observed MT motility. As Kinesin-1 has been identified as a robust MT-sliding motor in several model systems and cell types (Jolly et al 2010;Winding et al 2016;Straube et al 2006;Lu et al 2015;Lu et al 2022;Lu et al 2013;Lu et al 2016), we assessed the level of MT-motility in HeLa Kif5B KO cells (Serra-Marques et al 2020;) using the paGFPtubulin assay. However, we still observed clear translocation of photo-converted MT segments over time in absence of Kinesin-1, with the decrease in fluorescence signal in the initial photo-conversion region similar to the WT condition (Fig.…”