During cell division, spindle microtubules attach to chromosomes through kinetochores, protein complexes on the chromosome. The central question is how microtubules find kinetochores. According to the pioneering idea termed search-and-capture, numerous microtubules grow from a centrosome in all directions and by chance capture kinetochores. The efficiency of search-and-capture can be improved by a bias in microtubule growth towards the kinetochores, by nucleation of microtubules at the kinetochores and at spindle microtubules, by kinetochore movement, or by a combination of these processes. Here we show in fission yeast that kinetochores are captured by microtubules pivoting around the spindle pole, instead of growing towards the kinetochores. This pivoting motion of microtubules is random and independent of ATP-driven motor activity. By introducing a theoretical model, we show that the measured random movement of microtubules and kinetochores is sufficient to explain the process of kinetochore capture. Our theory predicts that the speed of capture depends mainly on how fast microtubules pivot, which was confirmed experimentally by speeding up and slowing down microtubule pivoting. Thus, pivoting motion allows microtubules to explore space laterally, as they search for targets such as kinetochores.
Trichoderma harzianum is a widely distributed soil fungus that antagonizes numerous fungal phytopathogens. The antagonism of T. harzianum usually correlates with the production of antifungal activities including the secretion of fungal cell walls that degrade enzymes such as chitinases. Chitinases Chit42 and Chit33 from T. harzianum CECT 2413, which lack a chitin-binding domain, are considered to play an important role in the biocontrol activity of this strain against plant pathogens. By adding a cellulose-binding domain (CBD) from cellobiohydrolase II of Trichoderma reesei to these enzymes, hybrid chitinases Chit33-CBD and Chit42-CBD with stronger chitin-binding capacity than the native chitinases have been engineered. Transformants that overexpressed the native chitinases displayed higher levels of chitinase specific activity and were more effective at inhibiting the growth of Rhizoctonia solani, Botrytis cinerea and Phytophthora citrophthora than the wild type. Transformants that overexpressed the chimeric chitinases possessed the highest specific chitinase and antifungal activities. The results confirm the importance of these endochitinases in the antagonistic activity of T. harzianum strains, and demonstrate the effectiveness of adding a CBD to increase hydrolytic activity towards insoluble substrates such as chitin-rich fungal cell walls.
Axon refinement is a necessary event for sculpting the final wiring of neural circuits. Although some factors have been identified that cause axonal arbor remodeling, the molecular pathways transducing these extracellular signals to adhesion disassembly and the cytoskeleton are poorly understood. Here we show that conditional ablation of Focal adhesion kinase (Fak) abolishes axon remodeling induced by Semaphorin-3A (Sema3A) in hippocampal neurons. Sema3A elicits divergent effects on different tyrosine residues of FAK: it increases phosphorylation of Tyr397, the kinase domain and the tyrosine residue 925, and decreases phosphorylation of Tyr407 and Tyr861. Moreover, Sema3A mediates mechanisms that contribute to the disassembly of adhesion contacts in a FAK-dependent manner: tyrosine phosphorylation of alpha-actinin and FAKY925 that decreases FAK-Paxillin interaction. Altogether, our results provide novel insights into the spatiotemporal dynamics of FAK activation mediated by Sema3A and on its interaction with its downstream effectors: Paxillin and alpha-actinin in neurons.
Pairing of homologous chromosomes is a crucial step in meiosis, which in fission yeast depends on nuclear oscillations. However, how nuclear oscillations help pairing is unknown. Here, we show that homologous loci typically pair when the spindle pole body is at the cell pole and the nucleus is elongated, whereas they unpair when the spindle pole body is in the cell center and the nucleus is round. Inhibition of oscillations demonstrated that movement is required for initial pairing and that prolonged association of loci leads to mis-segregation. The double-strand break marker Rec25 accumulates in elongated nuclei, indicating that prolonged chromosome stretching triggers recombinatory pathways leading to mis-segregation. Mis-segregation is rescued by overexpression of the Holliday junction resolvase Mus81, suggesting that prolonged pairing results in irresolvable recombination intermediates. We conclude that nuclear oscillations exhibit a dual role, promoting initial pairing and restricting the time of chromosome associations to ensure proper segregation.
During recombination, the DNA of parents exchange their genetic information to give rise to a genetically unique offspring. For recombination to occur, homologous chromosomes need to find each other and align with high precision. Fission yeast solves this problem by folding chromosomes in loops and pulling them through the viscous nucleoplasm. We propose a theory of pulled polymer loops to quantify the effect of drag forces on the alignment of chromosomes. We introduce an external force field to the concept of a Brownian bridge and thus solve for the statistics of loop configurations in space.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.