Spindle F-actin coordinates the first metaphase-anaphase transition in Drosophila meiosis

Abstract

Meiosis is a highly conserved feature of sexual reproduction that ensures germ cells have the correct number of chromosomes prior to fertilization. A subset of microtubules, known as the spindle, are essential for accurate chromosome segregation during meiosis. Building evidence in mammalian systems has recently highlighted the unexpected requirement of the actin cytoskeleton in chromosome segregation; a network of spindle actin filaments appear to regulate many aspects of this process. Here we show that Drosophila oocytes also have a spindle population of actin that regulates the formation of the microtubule spindle and chromosomal movements throughout meiosis. We demonstrate that genetic and pharmacological disruption of the actin cytoskeleton has a significant impact on spindle morphology, dynamics, and chromosome alignment and segregation during the metaphase-anaphase transition. We further reveal the requirement of calcium in maintaining the microtubule spindle and spindle actin. Together, our data highlights the significant conservation of morphology and mechanism of the spindle actin during meiosis.