Abstract
Cytoplasmic microtubules (cMT) control mitotic spindle positioning in many organisms, and are therefore pivotal for successful cell division. Despite its importance, the temporal control of cMT formation remains poorly understood. Here we show that unlike the best-studied yeast Saccharomyces cerevisiae, position of pre-anaphase nucleus is not strongly biased toward bud neck in Ogataea polymorpha and the regulation of spindle positioning becomes active only shortly before anaphase. This is likely due to the unstable property of cMTs compared to those in S. cerevisiae. Furthermore, we show that cMT nucleation/anchoring is restricted at the level of recruitment of the γ-tubulin complex receptor, Spc72, to spindle pole body (SPB), which is regulated by the polo-like kinase Cdc5. Additionally, electron microscopy revealed that the cytoplasmic side of SPB is structurally different between G1 and anaphase. Thus, polo-like kinase dependent recruitment of γ-tubulin receptor to SPBs determines the timing of spindle orientation in O. polymorpha.
Highlights
Segregation of sister chromatids into two daughter cells is pivotal to the proliferation of eukaryotic cells
In O. polymorpha, nuclear position was not biased to the bud neck, it remained in the mother cell body (Figure 1A, Figure 1—figure supplement 1)
The phenotype resembled, but was more exaggerated than, that in C. albicans where the nucleus is located with a distance from the bud neck in pre-anaphase cells (Martin et al, 2004; Finley et al, 2008)
Summary
Segregation of sister chromatids into two daughter cells is pivotal to the proliferation of eukaryotic cells. Chromosome segregation is followed by cytokinesis, which results in physical separation of two daughter cells. The position of the mitotic spindle dictates the site of cytokinesis, which ensures the inheritance and maintenance of genomic information in the daughter cells. Astral microtubules or cytoplasmic microtubules (cMTs), which emanate from the spindle poles and extend to the cell cortex, have a principle role in positioning and orienting the spindle with respect to the polarity cues of the cell type. Regulations that determine the timing of establishing the spindle orientation, or the position of the centrosome, the primary MT organizing centre (MTOC), in interphase, are not well understood (Kiyomitsu, 2015; Woyke et al, 2002)
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