Microtubule reorganization during female meiosis in C. elegans.

Ina Lantzsch,Hossein Yazdkhasti,Norbert Lindow,Vitaly Zimyanin,Erik Szentgyoergyi,Steffen Prohaska,Yu-Zen Chen,Sebastian Fürthauer,Martin Srayko,Stefanie Redemann,Che-Hang Yu,Ariel M Pani

doi:10.7554/elife.58903

Abstract

Most female meiotic spindles undergo striking morphological changes while transitioning from metaphase to anaphase. The ultra-structure of meiotic spindles, and how changes to this structure correlate with such dramatic spindle rearrangements remains largely unknown. To address this, we applied light microscopy, large-scale electron tomography and mathematical modeling of female meiotic Caenorhabditis elegans spindles. Combining these approaches, we find that meiotic spindles are dynamic arrays of short microtubules that turn over within seconds. The results show that the metaphase to anaphase transition correlates with an increase in microtubule numbers and a decrease in their average length. Detailed analysis of the tomographic data revealed that the microtubule length changes significantly during the metaphase-to-anaphase transition. This effect is most pronounced for microtubules located within 150 nm of the chromosome surface. To understand the mechanisms that drive this transition, we developed a mathematical model for the microtubule length distribution that considers microtubule growth, catastrophe, and severing. Using Bayesian inference to compare model predictions and data, we find that microtubule turn-over is the major driver of the spindle reorganizations. Our data suggest that in metaphase only a minor fraction of microtubules, those closest to the chromosomes, are severed. The large majority of microtubules, which are not in close contact with chromosomes, do not undergo severing. Instead, their length distribution is fully explained by growth and catastrophe. This suggests that the most prominent drivers of spindle rearrangements are changes in nucleation and catastrophe rate. In addition, we provide evidence that microtubule severing is dependent on katanin.

Highlights

During meiosis, haploid gametes are produced from diploid progenitor cells in most sexually reproducing eukaryotes
We find that female meiotic spindles are composed of arrays of short microtubules, 90% are shorter than half spindle length, which are highly dynamic and turnover within 10 s
The underlying mechanism of the microtubule reorganization is not very well understood, and several mechanisms could be involved, for instance, katanin-mediated severing as reported for C. elegans meiosis I (Joly et al, 2016; Srayko et al, 2006), transport of microtubules as reported for C. elegans and Xenopus meiotic spindles (Mullen and Wignall, 2017; Brugues et al, 2012), or changes in microtubule polymerization dynamics a shown for Xenopus meiotic spindles (Brugues et al, 2012; Needleman et al, 2010)

Summary

Introduction

Haploid gametes are produced from diploid progenitor cells in most sexually reproducing eukaryotes. We study the structure and dynamics of female meiotic spindles in Caenorhabditis elegans. Female meiotic spindles are assembled differently from those that rely on centrosome-based microtubule-organizing centers. This is true in humans (Holubcovaet al., 2015), mice (Schuh and Ellenberg, 2007), and in nematodes (Albertson and Thomson, 1993). The structural basis of these rearrangements and their role in meiotic chromosome segregation are not well understood It remains unclear whether these structural rearrangements are driven by katanin-mediated severing (Joly et al, 2016; Srayko et al, 2006), transport (Mullen and Wignall, 2017; Brugues et al, 2012), or changes in MT nucleation or polymerization dynamics (Brugues et al, 2012; Needleman et al, 2010). The rearrangements of spindle architecture towards anaphase are likely caused by changes in nucleation and not by any changes in cutting rates

Results

Discussion

Materials and methods

Funding Funder Deutsche Forschungsgemeinschaft