Pivot-and-bond model explains microtubule bundle formation

During mitosis, microtubules form a spindle, which is responsible for proper segregation of the genetic material. A common structural element in a mitotic spindle is a parallel bundle, consisting of two or more microtubules growing from the same origin and held together by cross-linking proteins. An interesting question is what are the physical principles underlying the formation and stability of such microtubule bundles. Here we show, by introducing the pivot-and-bond model, that random angular movement of microtubules around the spindle pole and forces exerted by cross-linking proteins can explain the formation of microtubule bundles as observed in our experiments. The model predicts that stable parallel bundles can form in the presence of either passive crosslinkers or plus-end directed motors, but not minus-end directed motors. In the cases where bundles form, the time needed for their formation depends mainly on the concentration of cross-linking proteins and the angular diffusion of the microtubule. In conclusion, the angular motion drives the alignment of microtubules, which in turn allows the cross-linking proteins to connect the microtubules into a stable bundle

VORBEREITUNG DER LEHRER FÜR AUFNAHME UND SCHULANFANG DER KINDER IN DER GRUNDSCHULE

Priprema djeteta za polazak u školu dulji je proces koji obuhvaća različita područja djetetova razvoja. Tradicionalni pristup pripreme djece i procjene njihove spremnosti za školu naglasak stavlja na ulogu odraslih, u prvom redu odgojitelja, koji su jedini kompetentni za tu zadaću. Osim odgojitelja i roditelja, važnu ulogu pripreme djece za polazak u osnovnu školu imaju učitelji. Važno je naglasiti da se djetetova spremnost za školu stvara tijekom prvih mjeseci školovanja, a ne prije polaska u školu. Kako bi se upoznali s predškolskom ustanovom i životom djece prije škole, u akademskoj 2010./11. godini studenti 5. godine Učiteljskoga fakulteta u više navrata boravili su u dječjem vrtiću. Hospitirali su kronološki homogenim (predškolskim) i heterogenim skupinama u kojima je raspon kronološke dobi bio od 3 do 7 godina. Studenti su svoju hospitaciju bilježili u unaprijed pripremljenim obrascima koji su sadržavali određena područja promatranja. Analiza bilježaka ukazuje na postojanje problema, točnije nerazumijevanja područja djetetova života u predškolskoj ustanovi, posebice u područjima ustrojstva aktivnosti te ustrojstva interakcije. To ukazuje na postojanje diskontinuiteta u pedagoškoj praksi između predškolske i osnovnoškolske ustanove. Stoga se ovim radom želi uputiti na potrebu mijenjanja aktualnih oblika suradnje odgojitelja i učitelja u smjeru pripreme učitelja i škole za prijem djeteta u osnovnu školu.Preparation of the child for departure in school is long process which includes different areas of child development. The traditional approach of preparing children and evaluating their readiness for school places emphasis on the role of adults, mostly pre-school teachers, who are only competent for this task. Except pre-school teachers and parents, an important part of preparing children for primary school has teachers. It is important to emphasize that the child\u27s readiness for school is formed during the first months of schooling, not before school. To be acquainted with pre-school institutions and the life of children before school, students of 5th year of Teacher’s University were in several occasions in kindergarten, during the academic year 2010. /2011. They were in the chronologically homogeneous (pre-school) and heterogeneous groups in which the chronological ages range were from 3 to 7 years. Students recorded their observation in advanced prepared forms that contained some of the certain areas. The analysis of the notes indicates to existence of problems, namely lack of understanding of the child’s life in the areas of pre-school institutions, particularly in the areas of organization and activities of the organization of interaction. This indicates the existence of discontinuity in the pedagogical practice between pre-school and primary school institutions. This paper aims to demonstrate the necessity of changing the current forms of cooperation of pre-school teachers and teachers in the direction of preparation of teachers and schools to receive a child in elementary schoolDas Vorbereiten des Kindes für die Schule ist ein langwieriger Prozess, der verschiedene Bereiche der kindlichen Entwicklung umfasst. Der traditionelle Ansatz zur Vorbereitung der Kinder und Beurteilung ihrer Bereitschaft für die Schule legt den Schwerpunkt auf die Rolle der Erwachsenen, meist Erzieher, die als Einzige kompetent für diese Aufgabe sind. Die Grundschullehrer spielen neben den Erziehern und Eltern eine wichtige Rolle bei der Vorbereitung der Kinder für den Schulanfang. Es ist wichtig zu betonen, dass die Bereitschaft des Kindes für die Schule in den ersten Schulmonaten gebildet wird, und nicht vor dem Schulbeginn. Um die vorschulischen Einrichtungen und das Leben der Kinder vor der Schule kennen zu lernen, besuchten die Studenten des 5. Studienjahres an der Fakultät für Lehrerbildung im akademischen Jahr 2010/2011 wiederholt einen Kindergarten. Sie besuchten die chronologisch homogenen (Vorschule) und heterogenen Gruppen, in denen die chronologische Alterspanne zwischen 3-7 Jahre war. Die Studenten haben ihre Hospitationen in vorbereitete Formulare eingetragen, die bestimmte Bereiche der Beobachtung enthielten. Die Analyse von Notizen wies auf bestehende Probleme hin, nämlich Mangel an Verständnis für den Bereich des Kindeslebens in der Vorschulinstitution, insbesondere in den Bereichen der Struktur von Aktivitäten und Interaktion. Dies deutet auf die Existenz einer Diskontinuität in der pädagogischen Praxis zwischen Vorschul- und Grundschulinstitutionen. Somit wollen wir mit diesem Beitrag auf die Notwendigkeit der Änderung von derzeitigen Formen der Zusammenarbeit zwischen Erziehern und Grundschullehrern hinweisen, nämlich in Richtung der Vorbereitung von Lehrern und der Schule für die Aufnahme des Kindes in die Grundschule

Microtubule Sliding within the Bridging Fiber Pushes Kinetochore Fibers Apart to Segregate Chromosomes

During cell division, mitotic spindle microtubules segregate chromosomes by exerting forces on kinetochores. What forces drive chromosome segregation in anaphase remains a central question. The current model for anaphase in human cells includes shortening of kinetochore fibers and separation of spindle poles. Both processes require kinetochores to be linked with the poles. Here we show, by combining laser ablation, photoactivation, and theoretical modeling, that kinetochores can separate without any attachment to one spindle pole. This separation requires the bridging fiber, a microtubule bundle that connects sister kinetochore fibers. Bridging fiber microtubules in intact spindles slide apart with kinetochore fibers, indicating strong crosslinks between them. We conclude that sliding of microtubules within the bridging fibers drives pole separation and pushes kinetochore fibers poleward by the friction of passive crosslinks between these fibers. Thus, sliding within the bridging fiber works together with the shortening of kinetochore fibers to segregate chromosomes

Microplastics in the Marine Environment of the Adriatic Sea

Plastika se zbog svoje široke uporabe može naći u svim dijelovima okoliša, gdje štetno utječe na različite sastavnice okoliša, a toksični spojevi koje adsorbira prenose se kroz hranidbene lance te s vremenom dolaze do čovjeka. Odabrana istraživanja u ovom radu usredotočena su na karakterizaciju i kvantifikaciju mikroplastike pronađene u Jadranskom moru kao i na toksičnost mikroplastike. Istraživanja su pokazala da je najviše mikroplastike detektirano u području Sjevernog Jadrana. Provedena ispitivanja ekotoksičnosti mikroplastike primjenom testa s algama ukazuju na to da mikroplastika uzrokuje smanjenje brzine rasta i kretanja algi, obavljanje fotosinteze, fizičke deformacije te dolazi do smanjenja plodnosti i promjena u metaboličkim ciklusima. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.The widespread use of plastics has led to the accumulation of plastics in all parts of the environment where it adversely affects the ecosystem. Plastic pollution has the biggest impact on the marine ecosystems which assimilate about 12.7 million tons of plastic yearly. Because of incomplete degradation, plastic in marine environment is accumulated in the form of large clusters and microplastic. Microplastic has a harmful impact on marine organisms due to the accumulation of toxic compounds adsorbed on its particles, which could be passed through the food chain and eventually to humans. Certain researches discussed in this paper are focused on the characterization and quantification of microplastic found in the Adriatic Sea. This work is licensed under a Creative Commons Attribution 4.0 International License

Paired arrangement of kinetochores together with microtubule pivoting and dynamics drive kinetochore capture in meiosis I

Kinetochores are protein complexes on the chromosomes, whose function as linkers between spindle microtubules and chromosomes is crucial for proper cell division. The mechanisms that facilitate kinetochore capture by microtubules are still unclear. In the present study, we combine experiments and theory to explore the mechanisms of kinetochore capture at the onset of meiosis I in fission yeast. We show that kinetochores on homologous chromosomes move together, microtubules are dynamic and pivot around the spindle pole, and the average capture time is 3-4 minutes. Our theory describes paired kinetochores on homologous chromosomes as a single object, as well as angular movement of microtubules and their dynamics. For the experimentally measured parameters, the model reproduces the measured capture kinetics and shows that the paired configuration of kinetochores accelerates capture, whereas microtubule pivoting and dynamics have a smaller contribution. Kinetochore pairing may be a general feature that increases capture efficiency in meiotic cells

Live cell X-ray imaging of autophagic vacuoles formation and chromatin dynamics in fission yeast

Seeing physiological processes at the nanoscale in living organisms without labeling is an ultimate goal in life sciences. Using X-ray ptychography, we explored in situ the dynamics of unstained, living fission yeast Schizosaccharomyces pombe cells in natural, aqueous environment at the nanoscale. In contrast to previous X-ray imaging studies on biological matter, in this work the eukaryotic cells were alive even after several ptychographic X-ray scans, which allowed us to visualize the chromatin motion as well as the autophagic cell death induced by the ionizing radiation. The accumulated radiation of the sequential scans allowed for the determination of a characteristic dose of autophagic vacuole formation and the lethal dose for fission yeast. The presented results demonstrate a practical method that opens another way of looking at living biological specimens and processes in a time-resolved label-free setting