Live imaging of the Drosophila ovarian niche shows spectrosome and centrosome dynamics during asymmetric germline stem cell division

Abstract

Drosophila female germline stem cells (GSCs) are found inside the cellular niche at the tip of the ovary. They undergo asymmetric divisions to renew the stem cell lineage and to produce sibling cystoblasts that will in turn enter differentiation. GSCs and cystoblasts contain spectrosomes, membranous structures essential to orientate the mitotic spindle and that, particularly in GSCs, change shape depending on the cell cycle phase. Using live imaging and a GFP fusion of the spectrosome component Par-1, we follow the complete spectrosome cycle throughout GSC division and quantify the relative duration of the different spectrosome shapes. We also determine that the Par-1 kinase shuttles between the spectrosome and the cytoplasm during mitosis and observe the continuous addition of new material to the GSC and cystoblast spectrosomes. Next, we utilise the Fly-FUCCI tool to define in live and fixed tissues that GSCs have a shorter G1 compared to the G2 phase. The observation of centrosomes in dividing GSCs allowed us to determine that centrosomes separate very early in G1, prior to centriole duplication. Furthermore, we show that the anterior centrosome associates with the spectrosome only during mitosis and that, upon mitotic spindle assembly, it translocates to the cell cortex, where it remains anchored until centrosome separation. Finally, we demonstrate that the asymmetric division of GSCs is not an intrinsic property of these cells, since the spectrosome of GSC-like cells located outside of the niche can divide symmetrically. Thus, GSCs display unique properties during division, a behaviour influenced by the surrounding niche.

The deubiquitinase USP8 targets ESCRT-III to promote incomplete cell division

“…This apparent contradiction could be explained by a major difference in cell cycle length between GSCs and germline cysts. GSCs cycle in 24 hours and take ~15 hours to complete abscission ( 23 , 24 ). In contrast, cysts go through four rounds of mitosis in 24 hours, that is, 6 hours for each cycle.…”

Regulation of Mating-Induced Increase in Female Germline Stem Cells in the Fruit Fly Drosophila melanogaster

“…In addition, it has not been elucidated whether the increase of female GSCs after mating is also implemented by the increase in dedifferentiation of the cysts ( Herrera and Bach, 2018 ). Therefore, in future, ex vivo live-imaging techniques for D. melanogaster ovaries ( Parton et al, 2010 ; He et al, 2011 ; Morris and Spradling, 2011 ; Cetera et al, 2016 ; Reilein et al, 2018 ; Villa-Fombuena et al, 2021 ), might be a powerful tool to resolve this debate. In particular, a recent report has optimized the experimental conditions that allow prolonged observation of ex vivo cultured germaria, and has succeeded in capturing the live images of both symmetric and asymmetric GSC division by visualizing the spectrosome cycle with GFP-fused Par-1 protein ( Villa-Fombuena et al, 2021 ).…”

Stress-induced reversible cell-cycle arrest requires PRC2/PRC1-mediated control of mitophagy in Drosophila germline stem cells and human iPSCs

“…To dissect the GSC reversible cell-cycle block in more detail we employed the IR-induced insult paradigm and fly fluorescent ubiquitination-based cell-cycle indicator (FUCCI) to visualize distinct cell-cycle stages in GSCs ( Zielke et al., 2014 ) ( Figures 1 C–1E). In the fly FUCCI line GFP-E2F1 1–230 is degraded by ubiquitin ligase CRL4 Cdt2 in S phase, and mRFP-CycB 1–266 is degraded by APC/C in late mitosis/G1 ( Figures 1 C and 1E) ( Zielke et al., 2014 ; Villa-Fombuena et al., 2021 ). Hence, FUCCI cells are green (GFP + /RFP − ) in G1, red (GFP − /RFP + ) in S, yellow (GFP + /RFP + ) in G2/M, and black (GFP − /RFP − ) in the G1-S transition ( Figures 1 C–1E).…”