Spatio-temporal regulation of nuclear division by Aurora B kinase Ipl1 in Cryptococcus neoformans

Abstract

The nuclear division takes place in the daughter cell in the basidiomycetous budding yeast Cryptococcus neoformans . Unclustered kinetochores gradually cluster and the nucleus moves to the daughter bud as cells enter mitosis. Here, we show that the evolutionarily conserved Aurora B kinase Ipl1 localizes to the nucleus upon the breakdown of the nuclear envelope during mitosis in C . neoformans . Ipl1 is shown to be required for timely breakdown of the nuclear envelope as well. Ipl1 is essential for viability and regulates structural integrity of microtubules. The compromised stability of cytoplasmic microtubules upon Ipl1 depletion results in a significant delay in kinetochore clustering and nuclear migration. By generating an in silico model of mitosis, we previously proposed that cytoplasmic microtubules and cortical dyneins promote atypical nuclear division in C . neoformans . Improving the previous in silico model by introducing additional parameters, here we predict that an effective cortical bias generated by cytosolic Bim1 and dynein regulates dynamics of kinetochore clustering and nuclear migration. Indeed, in vivo alterations of Bim1 or dynein cellular levels delay nuclear migration. Results from in silico model and localization dynamics by live cell imaging suggests that Ipl1 spatio-temporally influences Bim1 or/and dynein activity along with microtubule stability to ensure timely onset of nuclear division. Together, we propose that the timely breakdown of the nuclear envelope by Ipl1 allows its own nuclear entry that helps in spatio-temporal regulation of nuclear division during semi-open mitosis in C . neoformans .

Identification of bridgin, an unconventional linker, connects the outer kinetochore to centromeric chromatin

“…6f). The sharp reduction of AuroraB Ipl1 localization at anaphase kinetochores 48 and essentiality of amino-terminus of CENP-C Mif2 (Supplementary Fig. 6e and data not shown) are observed in C. neoformans.…”

“…We subsequently examined how bgi1Δ affected cell cycle progression. For this, microscopic markers to determine cell cycle stages previously determined 44, 48 were used and summarized in Supplementary Fig. 3c.…”

Aurora kinase Ipl1 facilitates bilobed distribution of clustered kinetochores to ensure error‐free chromosome segregation in Candida albicans

“…The kinetochores were shown to be randomly localized along the spindle axis having aberrant kMT lengths (Tytell and Sorger, ; Gardner et al , ; Marco et al , ). Recently, dynamic localization of Ipl1 has been shown to regulate the integrity of MTs required for timely nuclear migration and kinetochore clustering in Cryptococcus neoformans (Varshney et al , ).…”

Mechanics of MTOC clustering and spindle positioning in budding yeast Cryptococcus neoformans

“…Like S. cerevisiae, cells divide by budding in C. neoformans as well (Fig 1, S1 Video). The major sequence of mitotic events from the formation of bud until chromosome segregation in C. neoformans can be categorized in the following temporal order: (a) Bud inception at the end of G1/onset of S phase [16], (b) clustering of KTs as a single punctum at the periphery of nucleus after bud initiation [16] (Fig 1, S1 Video), (c) nuclear migration into the daughter bud followed by spindle formation; (d) localization of the spindle near the bud-neck junction/septin ring (Fig 1) and eventually (e) equal nuclear division mother and daughter bud (Fig 1, S1 Video).…”

“…(b) In S. cerevisiae, the KTs are grouped into a single cluster and KT attachments to the SPBs by MTs are maintained through most of the cell cycle [23,[28][29][30]. Contrary to that, in C. neoformans, KTs are unclustered during interphase [15,16,25]. As the cell advances through the cell cycle, the KTs gradually cluster into a single punctum, plausibly via various MT mediated interactions.…”