Microtubule polarity and axis formation in theDrosophila oocyte

Abstract

The body axes of the fruit fly are established in mid-oogenesis by the localization of three mRNA determinants, bicoid, oskar, and gurken, within the oocyte. General mechanisms of RNA localization and cell polarization, applicable to many cell types, have emerged from investigation of these determinants in Drosophila oogenesis. Localization of these RNAs is dependent on the germline microtubules, which reorganize to form a polarized array at mid-oogenesis in response to a signaling relay between the oocyte and the surrounding somatic follicle cells. Here we describe what is known about this microtubule reorganization and the signaling relay that triggers it. Recent studies have identified a number of ubiquitous RNA binding proteins essential for this process. So far, no targets for any of these proteins have been identified, and future work will be needed to illuminate how they function to reorganize microtubes and whether similar mechanisms also exist in other cell types.

Hsp60C is required in follicle as well as germline cells during oogenesis in Drosophila melanogaster

“…Mutations in genes encoding cell adhesion molecules such as Armadillo, DE-cadherin, Merlin, ␣-Spectrin, etc. affect follicle cell remodeling (Oda et al, 1997;Muller, 2000;MacDougall et al, 2001;Hudson and Cooley, 2002;Steinhauer and Kalderon, 2006), and the resulting phenotypes are in several ways similar to those seen in the Hsp60C 1 mutant egg chambers. In addition to the posterior group of follicle cells, Hsp60C is also essential for generating and maintaining a patterned monolayer of all other follicle cells as evidenced by the irregular arrangement of Hsp60C 1 /Hsp60C 1 follicle cells in mitotic clones, irrespective of their location and size (Fig.…”

“…The mode of interaction between Hsp60C and cytoskeletal components remains to be analyzed. The cytoskeletal elements and cadherin-mediated differential adhesion of the follicle cells are critical for their proliferation, migration, remodeling, fate adaptation, and for communication with nurse cells and the growing oocyte (Zhang and Kalderon, 2000;Steinhauer and Kalderon, 2006). Several actin-binding proteins are known to be essential for maintenance of cellular integrity and follicle cell morphogenesis during Drosophila oogenesis (Hudson and Cooley, 2002).…”

“…Posterior follicle cells in wild-type early egg chambers signal the posterior MTOC in oocyte for microtubule remodeling, which is responsible for the localization of several polarity determinants and movement of oocyte nucleus (Riechmann and Ephrussi, 2001;Steinhauer and Kalderon, 2006). Because Hsp60C 1 /Hsp60C 1 egg chambers showed abnormal distribution of actin and cell-adhesion proteins and aberrant arrangement of posterior follicle cells, we examined distribution of microtubules using anti-␣-tubulin antibody.…”

Spindle assembly in the oocytes of mouse and Drosophila – similar solutions to a problem

“…These nucleating centers could be numerous. Microtubule growth is nucleated from many organizing centers along the cortex of Drosophila oocytes prior to nuclear envelop breakdown as part of the axis specification during oogenesis (Theurkauf et al 1992, Cha et al 2002, Steinhauer & Kalderon 2006. Assembling the spindle, therefore, could be primarily done by the bundling and sliding of microtubule fibers, the result of which would be a structure composed of an overlapping array of many short fibers.…”

Oskar-induced endocytic activation and actin remodeling for anchorage of the Drosophila germ plasm

“…Pole plasm components are synthesized in the nurse cells and transported into the oocyte along the microtubule cytoskeleton emanating from the posterior end of the oocyte. 2 During stages 6-7, intercellular signaling between the oocyte and surrounding somatic follicle cells promotes the reorganization of oocyte polarity, such that the microtubule minus ends are lost from the oocyte posterior, and instead nucleate along the lateral and anterior cortex. The plus ends transiently accumulate in the middle of the oocyte at stage 7, and subsequently point to the posterior pole.…”