Three-dimensional reconstructions of the first mitotic spindle reveals a novel mechanism for spindle assembly in C. elegans

Date

Nov 13, 2014

Time

2:30 PM - 4:00 PM

Speaker

Dr. Stefanie Redemann

Affiliation

Müller-Reichert Lab, Medical theoretical centre, Dresden

Series

IMB - Seminar

Language

en

Main Topic

Biologie

Other Topics

Biologie

Description

Upon entering mitosis, the microtubule cytoskeleton of any eukaryotic organism undergoes a fundamental reorganization to form a bipolar spindle, which first aligns the condensed chromosomes on the metaphase plate and then segregates them to the resulting daughter cells. Despite the fact, that bipolar spindles are composed of the same building blocks and conduct the same function, there is a huge variety in spindle size, assembly and architecture across eukaryotic species. In order to understand spindle architecture, it is essential to understand the detailed 3D ultrastructure of a mitotic spindle and to quantitatively study the key features. We generated full 3D reconstructions of the first mitotic spindle in C. elegans during metaphase and anaphase using serial-section electron tomography. We combined this detailed structural data with dynamic data from light microscopy. Using this approach we were able to individually detect microtubules attaching to the holocentric kinetochores. This analysis provided us with detailed information on the number of microtubules attaching per chromosome, as well as the position of attachment sites on the chromosomes. To our surprise the percentage of kinetochore microtubules within the spindle is very small, only about 5%. In contrast to our expectations, we also discovered that the kinetochore microtubules do not origin at the centrosomes, but are polymerized on the kinetochores, most likely with the minus ends of the microtubules facing towards the centrosome. This suggests a yet undescribed mechanism in C. elegans, in which microtubules nucleated from centrosomes have to interact with microtubules originating from the kinetochores to form the bipolar mitotic spindle.

Last modified: Oct 22, 2014, 1:04:41 PM