MIHAELA JAGRIĆ – OBRANA DOKTORSKOG RADA

The role of kinesin-8 and PRC1 proteins in kinetochore positioning in the metaphase plate

Uloga proteina kinezina-8 i PRC1 u smještanju kinetohora u metafaznoj ravnini

utorak, 09. veljače 2021. godine u 16,00 sati putem on-line videokonferencije

- zainteresirani za dobivanje poveznice za pristup obrani molimo da se jave na mail pdsbiol@biol.pmf.hr

Povjerenstvo za obranu:

dr. sc. Juraj Simunić, znan. sur, IRB, Zagreb

izv. prof. dr. sc. Inga Urlić, PMF, Zagreb

Radhika Subramanian, PhD, Assistant Professor, Harvard University

Zamjena: prof. dr. sc. Mirjana Pavlica, PMF, Zagreb

 Mentor:

prof. dr. sc. Iva Tolić, Institut Ruđer Bošković, Zagreb

 SAŽETAK

In metaphase of mitosis, chromosomes align at the equatorial plane of the spindle, which is crucial for correct completion of later phases. Chromosome alignment is regulated by forces exerted by dynamics of kinetochore fibers (k-fibers) and polar ejection forces. This study explored a role of motor protein kinesin-8, which is known as one of main regulators of k-fiber dynamics, in chromosome alignment. Here, I showed that kinesin-8 regulates velocity and amplitude of kinetochore movements, while experiments of laser ablation of k-fibers after depletion of kinesin-8 indicate it has a role in limiting the growth of microtubules.

Furthermore, chromosome alignment could be influenced by bridging fibers, new class of microtubules in the spindle that connect sister k-fibers and balance the tension on sister kinetochores. This possibility is investigated by developing and applying optogenetic approach to manipulate localization of PRC1 protein, which specifically crosslinks microtubules within the bridging fibers. Acute removal of PRC1 led to disassembly of bridging fibers and elongation of their antiparallel overlaps, which was accompanied by misaligned and lagging chromosomes. Kif4A/kinesin-4 and Kif18A/kinesin-8 were also found within bridging fibers and largely lost upon PRC1 removal, suggesting that these proteins regulate the overlap length of bridging microtubules. Finally, I proposed a model where PRC1-mediated crosslinking of bridging microtubules and recruitment of kinesins to the bridging fiber promote chromosome alignment by overlap length-dependent forces transmitted to the associated k-fibers.