Microtubule‐dependent organization of subcortical microfilaments in the early Drosophila embryo

Abstract

Dynamic alterations in the spatial organization of cytoskeletal elements constitute a prominent morphological feature of the early, syncytial stages of embryogenesis in Drosophila. Here, we describe and characterize the dynamic behavior of cytoplasmic, subcortical microfilaments, which form a series of nucleus-associated structures, at different phases of the simultaneous nuclear division cycles characteristic of early Drosophila embryos. Remodeling of the cytoplasmic microfilament arrays takes place in parallel to the established cyclic reorganization of cortical microfilament structures. We provide evidence that the cortical and subcortical microfilament populations organize independently of each other, and in response to distinct instructive cues. Specifically, formation of subcortical microfilament structures appears to rely on, and spatially mirror, the organization of polarized microtubule arrays, while cortical microfilament restructuring constitutes a centrosome-dependent process. Genetic analysis identifies a requirement for SCAR, a key mediator of Arp2/3-based microfilament dynamics, in organization of subcortical microfilament structures. Developmental Dynamics 236:662-670, 2007.

Cortical movement of Bicoid in early Drosophila embryos is actin- and microtubule-dependent and disagrees with the SDD diffusion model

“…To investigate whether actin is involved in the movement, we subjected bcd +5+8 embryos to drugs such as phalloidin that prevents F-actin degradation ( S3A and S3B Fig ), or to latrunculin B that disrupts the formation of actin bundles ( S3C and S3D Fig ). In phalloidin-treated embryos, long cortical microfilaments (MFs) were observed ( S3B Fig ), consistent with a stabilization of F-actin [ 41 ]. In contrast, latrunculin B-treated embryos revealed absence of long MFs, and only globular actin particles were detected, instead ( S3D Fig ), demonstrating that these drugs can efficiently alter the actin cytoarchitecture.…”

Aster migration determines the length scale of nuclear separation in the Drosophila syncytial embryo

“…However, autonomous aster movement argues against nuclear migration driven solely by central spindle pushing (Foe et al, 1993). The reported ringlike arrangement of the most outer nuclei seen in fixed embryos (Baker et al, 1993) might be a consequence of an increasing density of the actin cytoskeleton toward the cell cortex (von Dassow and Schubiger, 1994; Foe et al, 2000; Riparbelli et al, 2007), possibly generating an exclusion zone that promotes ordered, directional expansion (Field and Lénárt, 2011). Gradual disassembly of an actin gel in this exclusion zone might assist the final stages of cortical migration (Hatanaka and Okada, 1991), requiring additional mechanisms, such as microtubule-based actin remodeling (Waterman-Storer et al, 2000), that are absent in our simplified cell-free system.…”