Shining light on Drosophila oogenesis: live imaging of egg development

Abstract

Drosophila oogenesis is a powerful model for the study of numerous questions in cell and developmental biology. In addition to its longstanding value as a genetically tractable model of organogenesis, recently it has emerged as an excellent system in which to combine genetics and live imaging. Rapidly improving ex vivo culture conditions, new fluorescent biosensors and photo-manipulation tools, and advances in microscopy have allowed direct observation in real time of processes such as stem cell self-renewal, collective cell migration, and polarized mRNA and protein transport. In addition, entirely new phenomena have been discovered, including revolution of the follicle within the basement membrane and oscillating assembly and disassembly of myosin on a polarized actin network, both of which contribute to elongating this tissue. This review focuses on recent advances in live-cell imaging techniques and the biological insights gleaned from live imaging of egg chamber development.

Figure 1

(a) Major stages of the Drosophila life cycle with the tissues and developmental events studied by live-cell imaging listed below. (b) Anatomy of fruit fly ovary and expanded view of egg chambers in a single ovariole. Germline stem cell self-renewal, follicle rotation, border cell migration, periodic actomyosin contraction, and polarized mRNA localization are further illustrated below. Arrows indicate the direction of movement (PGC: primordial germ cell; CNS: central nervous system; PNS: peripheral nervous system; NMJs: neuromuscular junctions; SOP: sensory organ precursor; GSC: germline stem cell; CB: cystoblast; EC: escort cell; FSC: follicle stem cell; FS: fusome; ECM: extracellular matrix; PC: polar cell; BC: border cell; NC: nurse cell; Myo: myosin; FAs: focal adhesion; MT: microtubule; Nos: nanos; Grk: gurken; and PCP: planar cell polarity).

Figure 2

(a) Timeline of Drosophila oogenesis with major developmental events labeled below. The beginning of each developmental stage is indicated by a mark on the line. The interval between stages was drawn in proportion to estimated development time. (b) Micrographs of major developmental stages of Drosophila oogenesis. Top panels show three-dimensional projections of z-stacks of confocal images with nuclei labeled in blue, E-cadherin labeled in green, and myosin labeled in red. Bottom panels show single-plane confocal images through the middle of the tissue with nuclei labeled in white, E-cadherin in green, and myosin in red. Scale bar is 50 μm.