Abstract
Purified microtubules have been shown to align along the static magnetic field (SMF) in vitro because of their diamagnetic anisotropy. However, whether mitotic spindle in cells can be aligned by magnetic field has not been experimentally proved. In particular, the biological effects of SMF of above 20 T (Tesla) have never been reported. Here we found that in both CNE-2Z and RPE1 human cells spindle orients in 27 T SMF. The direction of spindle alignment depended on the extent to which chromosomes were aligned to form a planar metaphase plate. Our results show that the magnetic torque acts on both microtubules and chromosomes, and the preferred direction of spindle alignment relative to the field depends more on chromosome alignment than microtubules. In addition, spindle morphology was also perturbed by 27 T SMF. This is the first reported study that investigated the cellular responses to ultra-high magnetic field of above 20 T. Our study not only found that ultra-high magnetic field can change the orientation and morphology of mitotic spindles, but also provided a tool to probe the role of spindle orientation and perturbation in developmental and cancer biology.
Highlights
The mitotic spindle is a highly dynamic microtubule assembly responsible for chromosome segregation and cleavage furrow positioning during cell division
Using immunofluorescence analysis of cells fixed immediately after they were taken out of the magnet, we found that mitotic spindle orientation was perturbed by 27 T static magnetic field (SMF) (Figure 3A)
We propose that the SMF-induced spindle orientation and morphology changes are due to the combined alignment effects of both microtubules and chromosomes in the magnetic field (Figure 8)
Summary
The mitotic spindle is a highly dynamic microtubule assembly responsible for chromosome segregation and cleavage furrow positioning during cell division. Spindle orientation is central to cell fate determination and tissue architecture, and mounting evidences show that astral microtubules, multiple cortical proteins and their interactions with plasma membrane are all critical to achieve correct orientation (Toyoshima et al, 2007; Lancaster and Knoblich, 2012; Lu and Johnston, 2013; Bergstralh and St Johnston, 2014; Nestor-Bergmann et al, 2014). SMFs can align large biological objects that have diamagnetic anisotropy, such as microtubule polymers and nucleic acid chains, as well as some types of cells and organisms (Maret and Dransfeld, 1977; Torbet and Ronziere, 1984; Higashi et al, 1993; Emura et al, 2001; Takeuchi et al, 2002; Teodori et al, 2006; Stern-Straeter et al, 2011). The degree of alignment with the externally applied magnetic field is proportional to the product of the molecular magnetic susceptibility and the magnetic field strength
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