Filopodia-like actin cables position nuclei in association with perinuclear actin in Drosophila nurse cells

Investigating spermatogenesis in Drosophila melanogaster

The process of spermatogenesis in Drosophila melanogaster provides a powerful model system to probe a variety of developmental and cell biological questions, such as the characterization of mechanisms that regulate stem cell behavior, cytokinesis, meiosis, and mitochondrial dynamics. Classical genetic approaches, together with binary expression systems, FRT-mediated recombination, and novel imaging systems to capture single cell behavior, are rapidly expanding our knowledge of the molecular mechanisms regulating all aspects of spermatogenesis. This methods chapter provides a detailed description of the system, a review of key questions that have been addressed or remain unanswered thus far, and an introduction to tools and techniques available to probe each stage of spermatogenesis.

Distinct roles for hu li tai shao and swallow in cytoskeletal organization during Drosophila oogenesis

BACKGROUND

Cytoskeletal organization is essential for localization of developmentally significant molecules during Drosophila oogenesis. Swallow (Swa) and an isoform of Hu li tai shao (Ovhts-RC) have been implicated in the organization of actin filaments in developing oocytes but their precise roles have been obscured by the dependence of hts RNA localization on swa function. The functional significance of hts RNA localization in the oocyte has not been established.

RESULTS

In this study we examine Ovhts-RC distribution and cytoskeletal organization under conditions in which Swa protein and/or hts RNA localization are perturbed. We find Swa is required for overall actin organization and for the maintenance of a distinct subset of microtubules in the oocyte. hts RNA localization modulates the distribution of Ovhts-RC in the oocyte and, in turn, local actin filament proliferation.

CONCLUSIONS

Our results support separate contributions of Swa and hts RNA localization to actin organization during oogenesis. Swa is crucial for the organization of actin networks that lead to the formation of a specialized microtubule population, while Ovhts-RC acts to modulate spatially restricted actin filament growth at the oocyte cortex. This suggests RNA localization can lead to modifications of both the actin and microtubule cytoskeletons at specific subcellular locales.

Tissue guidance without filopodia

Filopodia are highly dynamic, rod-like protrusions that are found in abundance at the leading edge of migrating cells such as endothelial tip cells and at axonal growth cones of developing neurons. One proposed function of filopodia is that of an environmental probe, which serves to sense guidance cues during neuronal pathfinding and blood vessel patterning. However, recent studies show that tissue guidance occurs unhindered in the absence of filopodia, suggesting a dispensability of filopodia in this process. Here, we discuss evidence that support as well as dispute the role of filopodia in guiding the formation of stereotypic neuronal and blood vessel patterns.

Methods for studying oogenesis

Drosophila oogenesis is an excellent system for the study of developmental cell biology. Active areas of research include stem cell maintenance, gamete development, pattern formation, cytoskeletal regulation, intercellular communication, intercellular transport, cell polarity, cell migration, cell death, morphogenesis, cell cycle control, and many more. The large size and relatively simple organization of egg chambers make them ideally suited for microscopy of both living and fixed whole mount tissue. A wide range of tools is available for oogenesis research. Newly available shRNA transgenic lines provide an alternative to classic loss-of-function F2 screens and clonal screens. Gene expression can be specifically controlled in either germline or somatic cells using the Gal4/UAS system. Protein trap lines provide fluorescent tags of proteins expressed at endogenous levels for live imaging and screening backgrounds. This review provides information on many available reagents and key methods for research in oogenesis.

Prostaglandins temporally regulate cytoplasmic actin bundle formation during Drosophila oogenesis

Tight regulation of actin remodeling is essential for development, and misregulation results in disease. Cytoskeletal dynamics are regulated by prostaglandins (PGs)—lipid signals. PGs temporally regulate actin remodeling during Drosophila oogenesis, at least in part, by modulating the activity of the actin elongation factor Enabled.

Prostaglandins (PGs)—lipid signals produced downstream of cyclooxygenase (COX) enzymes—regulate actin dynamics in cell culture and platelets, but their roles during development are largely unknown. Here we define a new role for Pxt, the Drosophila COX-like enzyme, in regulating the actin cytoskeleton—temporal restriction of actin remodeling during oogenesis. PGs are required for actin filament bundle formation during stage 10B (S10B). In addition, loss of Pxt results in extensive early actin remodeling, including actin filaments and aggregates, within the posterior nurse cells of S9 follicles; wild-type follicles exhibit similar structures at a low frequency. Hu li tai shao (Hts-RC) and Villin (Quail), an actin bundler, localize to all early actin structures, whereas Enabled (Ena), an actin elongation factor, preferentially localizes to those in pxt mutants. Reduced Ena levels strongly suppress early actin remodeling in pxt mutants. Furthermore, loss of Pxt results in reduced Ena localization to the sites of bundle formation during S10B. Together these data lead to a model in which PGs temporally regulate actin remodeling during Drosophila oogenesis by controlling Ena localization/activity, such that in S9, PG signaling inhibits, whereas at S10B, it promotes Ena-dependent actin remodeling.