Caveolae promote successful abscission by controlling intercellular bridge tension during cytokinesis

During cytokinesis, the intercellular bridge (ICB) connecting the daughter cells experiences pulling forces, which delay abscission by preventing the assembly of the ESCRT scission machinery. Abscission is thus triggered by tension release, but how ICB tension is controlled is unknown. Here, we report that caveolae, which are known to control membrane tension upon mechanical stress in interphase cells, are located at the midbody, at the abscission site and at the ICB/cell interface in dividing cells. Functionally, the loss of caveolae delays ESCRT-III recruitment during cytokinesis and impairs abscission. This is the consequence of a 2-fold increase of ICB tension measured by laser ablation, associated with a local increase in myosin II activity at the ICB/cell interface. We thus propose that caveolae buffer membrane tension and limit contractibility at the ICB to promote ESCRT-III assembly and cytokinetic abscission. Altogether, this work reveals an unexpected connection between caveolae and the ESCRT machinery and the first role of caveolae in cell division.

SSNA1 stabilizes dynamic microtubules and detects microtubule damage

Sjögren's Syndrome Nuclear Autoantigen 1 (SSNA1/NA14) is a microtubule-associated protein with important functions in cilia, dividing cells and developing neurons. However, the direct effects of SSNA1 on microtubules are not known. We employed in vitro reconstitution with purified proteins and TIRF microscopy to investigate the activity of human SSNA1 on dynamic microtubule ends and lattices. Our results show that SSNA1 modulates all parameters of microtubule dynamic instability - slowing down the rates of growth, shrinkage and catastrophe, and promoting rescue. We find that SSNA1 forms stretches along growing microtubule ends and binds cooperatively to the microtubule lattice. Furthermore, SSNA1 is enriched on microtubule damage sites, occurring both naturally, as well as induced by the microtubule severing enzyme spastin. Finally, SSNA1 binding protects microtubules against spastin's severing activity. Taken together, our results demonstrate that SSNA1 is both a potent microtubule stabilizing protein and a novel sensor of microtubule damage; activities that likely underlie SSNA1's functions on microtubule structures in cells.

Expression of KRAS in tissue samples of colorectal carcinoma and its correlation with various histo-pathological parameters.

Objective: To assess the expression of KRAS in tissue samples of colorectal carcinoma and to correlate it with histopathological parameters. Study Design: Cross Sectional study. Setting: Department of Pathology, PNS Shifa Hospital Karachi. Period: March 2016 to February 2019. Material & Methods: A total of 51 cases of CRC were analyzed for immunohistochemical staining using KRAS antibody on representative tissue blocks. Clinical and pathological records were retrieved for collection of data. The results of immunohistochemical analysis were correlated with the recorded clinico-pathological parameters. Results: In this study 51 cases of CRC were analyzed for immunoexpression of KRAS. The age of the patients ranged from 14 to 85 years with the mean age of 60.96 years. Among the 51 cases, 37(72.5%) cases were males and 14(27.4%) were females. 37(72.5%) were localized to left side colon and 14(27.4%) were found in the right colon. For KRAS immunostaining, 41(80.3%) out of 51 cases showed overexpression. Significant association was seen between KRAS overexpression and histological variants i.e. glandular carcinomas. Conclusion: In the present study over expression of KRAS was observed in advanced tumors. Majority of these cases were adenocarcinomas with few showed mucinous histology. The present study signifies that established KRAS expression is usually seen in rapidly dividing cells with association of advanced tumors.

The cytogenetic parameters of Pinus sylvestris L. under conditions of the Far North of Russia (Karelia)

The cytogenetic analysis of the Pinus sylvestris L. seed progeny in the forests of the northern taiga in the Far North of Russia conditions was carried out. Two Pinus sylvestris populations growing in Ambarnskoy and Pyaozerskoy forest divisions of Loukhsky district of Karelia Republic were studied. The number of chromosomes, the frequency and types of mitosis disturbances at the metaphase, anaphase and telophase (as a percentage of the total number of dividing cells at the same stages), and the frequency of micronuclei occurrence, as well as the laboratory seed germination, were studied. As a result of the study, it was found that 50–56% of the studied sprouts were mixoploid. Analysis of mitosis showed that the root meristem of the studied samples contained cells with various pathologies; simultaneously, the frequency of mitosis pathologies in the Ambarnskoy population was significantly higher than in the Pyaozerskoy one. It amounted to 6.8 ± 0.4 and 4.9 ± 0.4%, respectively. Nine types of abnormalities were identified; chromosome overrun and bridges prevailed. Micronuclei were registered in 35–38% of the studied Pinus sylvestris sprouts. At the same time, the proportion of cells with micronuclei in the Ambarnskoy population was 2-fold higher than in the Pyaozerskoy one and averaged 0.12 ± 0.03% and 0.07 ± 0.02%, respectively.

Unicellular-Multicellular Evolutionary Branching Driven by Resource Limitations

Multicellular life forms have evolved many times in our planet, suggesting that this is a common evolutionary innovation. Multiple advantages have been proposed for multicellularity (MC) to emerge. In this paper we address the problem of how the first precondition for multicellularity, namely "stay together" might have occurred under spatially limited resources exploited by a population of unicellular agents. Using a minimal model of evolved cell-cell adhesion among growing and dividing cells that exploit a localised resource with a given size, we show that a transition occurs at a critical resource size separating a phase of evolved multicellular aggregates from a phase where unicellularity (UC) is favoured. The two phases are separated by an intermediate domain where where both UC and MC can be selected by evolution. This model provides a minimal approach to the early stages that were required to transition from Darwinian individuality to cohesive groups of cells associated with a physical cooperative effect: when resources are present only in a localised portion of the habitat, MC is a desirable property as it helps cells to keep close to the available local nutrients.

Opto-Katanin: An Optogenetic Tool for Localized Microtubule Disassembly

Microtubules are major cytoskeletal filaments that drive chromosome separation during cell division, serve as rails for intracellular transport and as a scaffold for organelle positioning. Experimental manipulation of microtubules is widely used in cell and developmental biology, but tools for precise subcellular spatiotemporal control of microtubule integrity are currently lacking. Here, we exploit the dependence of the mammalian microtubule-severing protein katanin on microtubule-targeting co-factors to generate a light-activated system for localized microtubule disassembly that we named opto-katanin. Targeted illumination with blue light induces rapid and localized opto-katanin recruitment and local microtubule depolymerization, which is quickly reversible after stopping light-induced activation. Opto-katanin can be employed to locally perturb microtubule-based transport and organelle morphology in dividing cells and differentiated neurons with high spatiotemporal precision. We show that different microtubule-associated proteins can be used to recruit opto-katanin to microtubules and induce severing, paving the way for spatiotemporally precise manipulation of specific microtubule subpopulations.

Simulating the Interplay between the Uptake of Inorganic Phosphate and the Cell Phosphate Metabolism under Phosphorus Feast and Famine Conditions in Chlorella vulgaris

Using a mathematical simulation approach, we studied the dynamics of the green microalga Chlorella vulgaris phosphate metabolism response to shortage and subsequent replenishing of inorganic phosphate in the medium. A three-pool interaction model was used to describe the phosphate uptake from the medium, its incorporation into the cell organic compounds, its storage in the form of polyphosphates, and culture growth. The model comprises a system of ordinary differential equations. The distribution of phosphorous between cell pools was examined for three different stages of the experiment: growth in phosphate-rich medium, incubation in phosphate-free medium, and phosphate addition to the phosphorus-starving culture. Mathematical modeling offers two possible scenarios for the appearance of the peak of polyphosphates (PolyP). The first scenario explains the accumulation of PolyP by activation of the processes of its synthesis, and the decline in PolyP is due to its redistribution between dividing cells during growth. The second scenario includes a hysteretic mechanism for the regulation of PolyP hydrolysis, depending on the intracellular content of inorganic phosphate. The new model of the dynamics of P pools in the cell allows one to better understand the phenomena taking place during P starvation and re-feeding of the P-starved microalgal cultures with inorganic phosphate such as transient PolyP accumulation. Biotechnological implications of the observed dynamics of the polyphosphate pool of the microalgal cell are considered. An approach enhancing the microalgae-based wastewater treatment method based on these scenarios is proposed.

Cell-Projection Pumping of Fibroblast Contents into Osteosarcoma SAOS-2 Cells Correlates with Increased SAOS-2 Proliferation and Migration, as well as Altered Morphology

We earlier reported that cell-projection pumping transfers fibroblast contents to cancer cells and this alters the cancer cell phenotype. Here, we report on single-cell tracking of time lapse recordings from co-cultured fluorescent fibroblasts and SAOS-2 osteosarcoma cells, tracking 5201 cells across 7 experiments. The fluorescent lipophilic marker DiD was used to label fibroblast organelles and to trace the transfer of fibroblast cytoplasm into SAOS-2 cells. We related SAOS-2 phenotypic change to levels of fluorescence transfer from fibroblasts to SAOS-2 cells, as well as what we term ‘compensated fluorescence’, that numerically projects mother cell fluorescence post-mitosis into daughter cells. The comparison of absolute with compensated fluorescence allowed us to deduct if the phenotypic effects in mother SAOS-2 cells were inherited by their daughters. SAOS-2 receipt of fibroblast fluorescence correlated by Kendall’s tau with cell-profile area and without evidence of persistence in daughter cells (median tau = 0.51, p < 0.016); negatively and weakly with cell circularity and with evidence of persistence (median tau = −0.19, p < 0.05); and very weakly with cell migration velocity and without evidence of persistence (median tau = 0.01, p < 0.016). In addition, mitotic SAOS-2 cells had higher rates of prior fluorescence uptake (median = 64.9 units/day) than non-dividing cells (median = 35.6 units/day, p < 0.016) and there was no evidence of persistence post-mitosis. We conclude that there was an appreciable impact of cell-projection pumping on cancer cell phenotype relevant to cancer histopathological diagnosis, clinical spread and growth, with most effects being ‘reset’ by cancer cell mitosis.

Morphofunctional features of proliferating cells exposed to PSMA peptide

The effect of the synthetic PSMA peptide on dividing cells of laboratory animals was studied. The experiment was carried out on male white laboratory mice of the BALB/c-line. The toxic effect of PSMA peptidi was evaluated at therapeutic (1.4 μg / kg of animal weight or 0.04 μg / animal) and subtoxic (140 μg / kg of animal weight or 4.0 μg / animal) doses. The cytotoxic effect of PSMA peptide on red bone marrow cells and cambial intestinal cells of the of laboratory mice was determined. A decrease in the proliferative activity of the colon crypt cells was revealed upon administration of a subtoxic dose of the PSMA peptide and there were no signs of toxic damage to the red bone marrow cells of animals. Key words: toxicity, proliferation, synthetic peptides, mitotic index, micronucleus test.