The role of microtubule pivoting in formation of antiparallel microtubule bundles

Tijekom stanične diobe, genetski se materijal dijeli u dva jednaka djela pomoću diobenog vretena. Diobeno je vreteno poput kompleksnog mikro-stroja kojeg čine kromosomi, mikrotubuli koji se protežu iz dva pola prema kromosomima te motorni proteini. Dio mikrotubula koji se protežu iz jednog pola diobenog vretena veže se s mikrotubulima koji se protežu iz suprotnog pola te na taj način formiraju antiparalelne svežnjeve. Formiranje i stabilnost ovih struktura osiguravaju motorni proteini. Međutim, fizikalni principi formiranja antiparalelnih svežnjeva još uvijek nisu poznati. U ovom radu razvijamo teorijski opis procesa formiranja antiparalelnih svežnjeva mikrotubula koji je motiviran najnovijim eksperimentima naših suradnika. Model uključuje nasumično kutno gibanje mikrotubula oko polova diobenog vretena uzrokovano termalnim fluktuacijama te privlačne sile kojima motorni proteini djeluju na mikrotubule. Kad su mikrotubuli dovoljno blizu jedan drugom, motorni proteini se vežu za njih, te svojim kretanjem prema polovima generiraju sile koje zakreću mikrotubule prema antiparalelnoj konfiguraciji. Ovaj model pokazuje da termalne fluktuacije i sile koje stvaraju motorni proteini omogućuju nastajanje antiparalelnih svežnjeva.During cell division, the genetic material is divided into two equal parts by the mitotic spindle. This complex dynamic micro-machine is made of chromosomes, microtubules extending from two poles and a variety of accessory proteins. Microtubules extending from one spindle pole bind to those from the other spindle pole by motors and other crosslinking proteins, forming antiparallel bundles that comprise the spindle. Formation and stability of these structures is mediated by motor proteins. However, the physical principles behind the formation of antiparallel microtubule bundles are still not known. In this work we develop a theoretical description of the formation of antiparallel microtubule bundles motivated by the newest experimental work done by our collaborators. Our model includes the angular movement of microtubules around spindle poles and attractive forces exerted by motor proteins walking along the microtubules and cross-linking them. When two microtubules are found in close proximity to each other, motor proteins cross-link them and move towards the poles creating forces, which move the microtubules towards an antiparallel configuration. This model shows that thermal fluctuations and forces exerted by motor proteins facilitate formation of antiparallel microtubule bundles

Impact of harvest date on the content of volatile components in garlic

The aim of this study was to define optimal harvesting date of garlic cv. \u27Istarski crveni\u27 by comparing the amount of volatile compounds as one of quality indicators. In total 17 volatile compounds were determined in tested garlic samples by headspace solid-phase microextraction coupled to gas chromatography with flame ionization and mass spectrometric detection (HS-SPME-GC-FID-MS) regardless of harvesting date. Major volatiles diallyl trisulfide, diallyl sulfide, methyl allyl disulfide and diallyl disulfide representing 98.5 % of all the determined compounds have shown no significant difference between harvest dates. Significantly higher content of the two minor volatiles, allyl mercaptane and thieno[2,3-b]thiophene, was found in the last and second when compared to the first harvest date. Principal components PC1 and PC2 explained 78% of the total variance and pointed to certain relations between harvest dates and volatiles. The technological maturity had probably been reached at the first harvesting date since similar amounts of volatiles were found during the observed period

Glia in amyotrophic lateral sclerosis and spinal cord injury: common therapeutic targets

The toolkit for repairing damaged neurons in amyotrophic lateral sclerosis (ALS) and spinal cord injury (SCI) is extremely limited. Here, we reviewed the in vitro and in vivo studies and clinical trials on nonneuronal cells in the neurodegenerative processes common to both these conditions. Special focus was directed to microglia and astrocytes, because their activation and proliferation, also known as neuroinflammation, is a key driver of neurodegeneration. Neuroinflammation is a multifaceted process that evolves during the disease course, and can be either beneficial or toxic to neurons. Given the fundamental regulatory functions of glia, pathogenic mechanisms in neuroinflammation represent promising therapeutic targets. We also discussed neuroprotective, immunosuppressive, and stem-cell based approaches applicable to both ALS and SCI

Absolute frequency measurement of the 5s5p 1P1^1P_1 - 5s5d 1D2^1D_2 transition in strontium

We report on the absolute frequency determination of the 5s5p $^1P_1$ - 5s5d $^1D_2$ transition in atomic strontium, achieved through frequency comb-referenced laser-induced-fluorescence (LIF) spectroscopy. We excite the 5s$^2$ $^1S_0$ - 5s5p $^1P_1$ transition using an on-resonance laser at $\approx$461 nm, and then measure the variation in the LIF signal while scanning the laser at $\approx$767 nm across the 5s5p $^1P_1$ - 5s5d $^1D_2$ transition. We determine the absolute frequency of $390599571.7\pm0.4$ MHz, with an accuracy that surpasses the previous most accurate measurement by two orders of magnitude. This measurement technique can be readily applied for precision spectroscopy of high-lying states not only in strontium, but also in other atomic species

The effect of biostimulant and fertilizer on “low input” lettuce production

Lettuce production in the winter on the Adriatic coast, especially in a non-heated plastic tunnel, requires longer cultivation and is characterised by lower head mass and yield. In these conditions, the effect of biostimulant Bio-algeen S-90 and fertilizer Megagreen on the production of the traditional winter lettuce cultivar ‘Four Seasons’ was tested. Both treatments showed a positive effect on the growth and total yield of winter lettuce, and decreased the share of non-marketable yield. Bio-algeen S-90 treatment increased the plant height by 61.5%, and foliar treatment with Megagreen by 60.9%, as compared to the control treatment. Equally, both treatments resulted in higher leaf numbers (47.7% for Bio-algeen S-90 and 37.2% for Megagreen). The head mass of lettuce treated with Bio-algeen S-90 and Megagreen was 30.3% and 25.0% higher than in the control treatment, respectively. Megagreen contributed more to chlorophyll and carotenoid content, while Bio-algeen S-90 elevated the amount of vitamin C and dry matter. The pH value of lettuce juice decreased after Bio-algeen S-90, while the mineral content (N, P and K) did not differ between the tested treatments. Lower nitrate content was detected after both treatments. The obtained results elucidate the effect of Bio-algeen S-90 and Megagreen on “low input” lettuce production

Pivoting of microtubules driven by minus-end-directed motors leads to spindle assembly

Background At the beginning of mitosis, the cell forms a spindle made of microtubules and associated proteins to segregate chromosomes. An important part of spindle architecture is a set of antiparallel microtubule bundles connecting the spindle poles. A key question is how microtubules extending at arbitrary angles form an antiparallel interpolar bundle. Results Here, we show in fission yeast that microtubules meet at an oblique angle and subsequently rotate into antiparallel alignment. Our live- cell imaging approach provides a direct observation of interpolar bundle formation. By combining experiments with theory, we show that microtubules from each pole search for those from the opposite pole by performing random angular movement. Upon contact, two microtubules slide sideways along each other in a directed manner towards the antiparallel configuration. We introduce the contour length of microtubules as a measure of activity of motors that drive microtubule sliding, which we used together with observation of Cut7/kinesin-5 motors and our theory to reveal the minus-end- directed motility of this motor in vivo. Conclusion Random rotational motion helps microtubules from the opposite poles to find each other and subsequent accumulation of motors allows them to generate forces that drive interpolar bundle formation

Archaeal aminoacyl-tRNA synthetases interact with the ribosome to recycle tRNAs

Aminoacyl-tRNA synthetases (aaRS) are essential enzymes catalyzing the formation of aminoacyl-tRNAs, the immediate precursors for encoded peptides in ribosomal protein synthesis. Previous studies have suggested a link between tRNA aminoacylation and high-molecular-weight cellular complexes such as the cytoskeleton or ribosomes. However, the structural basis of these interactions and potential mechanistic implications are not well understood. To biochemically characterize these interactions we have used a system of two interacting archaeal aaRSs: an atypical methanogenic-type seryl-tRNA synthetase and an archaeal ArgRS. More specifically, we have shown by thermophoresis and surface plasmon resonance that these two aaRSs bind to the large ribosomal subunit with micromolar affinities. We have identified the L7/L12 stalk and the proteins located near the stalk base as the main sites for aaRS binding. Finally, we have performed a bioinformatics analysis of synonymous codons in the Methanothermobacter thermautotrophicus genome that supports a mechanism in which the deacylated tRNAs may be recharged by aaRSs bound to the ribosome and reused at the next occurrence of a codon encoding the same amino acid. These results suggest a mechanism of tRNA recycling in which aaRSs associate with the L7/L12 stalk region to recapture the tRNAs released from the preceding ribosome in polysome