Size of the cell nucleus and its effect on the chromatin structure in living cells.

DNA-architectural proteins play a major role in organization of chromosomal DNA in living cells by packaging it into chromatin, whose spatial conformation is determined by an intricate interplay between the DNA-binding properties of architectural proteins and physical constraints applied to the DNA by a tight nuclear space. Yet, the exact effects of the cell nucleus size on DNA-protein interactions and chromatin structure currently remain obscure. Furthermore, there is even no clear understanding of molecular mechanisms responsible for the nucleus size regulation in living cells. To find answers to these questions, we developed a general theoretical framework based on a combination of polymer field theory and transfer-matrix calculations, which showed that the nucleus size is mainly determined by the difference between the surface tensions of the nuclear envelope and the endoplasmic reticulum membrane, as well as the osmotic pressure created by cytosolic macromolecules on the cell nucleus. In addition, the model predicted the existence of a previously unknown link between the cell nucleus size and stability of nucleosomes, providing new insights into the potential role of nuclear organization in shaping the cell response to environmental cues.

A contour property based approach to segment nuclei in cervical cytology images

Background Segmentation of nuclei in cervical cytology pap smear images is a crucial stage in automated cervical cancer screening. The task itself is challenging due to the presence of cervical cells with spurious edges, overlapping cells, neutrophils, and artifacts. Methods After the initial preprocessing steps of adaptive thresholding, in our approach, the image passes through a convolution filter to filter out some noise. Then, contours from the resultant image are filtered by their distinctive contour properties followed by a nucleus size recovery procedure based on contour average intensity value. Results We evaluate our method on a public (benchmark) dataset collected from ISBI and also a private real dataset. The results show that our algorithm outperforms other state-of-the-art methods in nucleus segmentation on the ISBI dataset with a precision of 0.978 and recall of 0.933. A promising precision of 0.770 and a formidable recall of 0.886 on the private real dataset indicate that our algorithm can effectively detect and segment nuclei on real cervical cytology images. Tuning various parameters, the precision could be increased to as high as 0.949 with an acceptable decrease of recall to 0.759. Our method also managed an Aggregated Jaccard Index of 0.681 outperforming other state-of-the-art methods on the real dataset. Conclusion We have proposed a contour property-based approach for segmentation of nuclei. Our algorithm has several tunable parameters and is flexible enough to adapt to real practical scenarios and requirements.

Hyperpolyploidization of hepatocyte initiates preneoplastic lesion formation in the liver

Hepatocellular carcinoma (HCC) is the most predominant primary malignancy in the liver. Genotoxic and genetic models have revealed that HCC cells are derived from hepatocytes, but where the critical region for tumor foci emergence is and how this transformation occurs are still unclear. Here, hyperpolyploidization of hepatocytes around the centrilobular (CL) region is demonstrated to be closely linked with the development of HCC cells after diethylnitrosamine treatment. We identify the CL region as a dominant lobule for accumulation of hyperpolyploid hepatocytes and preneoplastic tumor foci formation. We also demonstrate that upregulation of Aurkb plays a critical role in promoting hyperpolyploidization. Increase of AURKB phosphorylation is detected on the midbody during cytokinesis, causing abscission failure and hyperpolyploidization. Pharmacological inhibition of AURKB dramatically reduces nucleus size and tumor foci number surrounding the CL region in diethylnitrosamine-treated liver. Our work reveals an intimate molecular link between pathological hyperpolyploidy of CL hepatocytes and transformation into HCC cells.

Activity of the first interstellar comet 2I/Borisov around perihelion: results from Indian observatories

ABSTRACT Comet 2I/Borisov is the first true interstellar comet discovered. Here, we present results from observational programs at two Indian observatories, 2 m Himalayan Chandra Telescope at the Indian Astronomical Observatory, Hanle (HCT) and 1.2 m telescope at the Mount Abu Infrared Observatory (MIRO). Two epochs of imaging and spectroscopy were carried out at the HCT and three epochs of imaging at MIRO. We found CN to be the dominant molecular emission on both epochs, 2019 November 30 and December 22, at distances of rH = 2.013 and 2.031 au, respectively. The comet was inferred to be relatively depleted in Carbon bearing molecules on the basis of low C2 and C3 abundances. We find the production rate ratio, Q(C2)/Q(CN) = 0.54 ± 0.18, pre-perihelion and Q(C2)/Q(CN) = 0.34 ± 0.12 post-perihelion. This classifies the comet as being moderately depleted in carbon chain molecules. Using the results from spectroscopic observations, we believe the comet to have a chemically heterogeneous surface having variation in abundance of carbon chain molecules. From imaging observations, we infer a dust-to-gas ratio similar to carbon chain depleted comets of the Solar system. We also compute the nucleus size to be in the range 0.18 km ≤ r ≤ 3.1 km. Our observations show that 2I/Borisov’s behaviour is analogous to that of the Solar system comets.

Yolk platelets impede nuclear expansion in Xenopus embryos

ABSTRACTDuring metazoan early embryogenesis, the intracellular properties of proteins and organelles change dynamically through rapid cleavage. In particular, a change in the nucleus size is known to contribute to embryonic development-dependent cell cycle and gene expression regulation. Here, we compared the nuclear sizes of various blastomeres from developing Xenopus embryos and analyzed the mechanisms that control the nuclear expansion dynamics by manipulating the amount of intracellular components in a cell-free system. There was slower nuclear expansion during longer interphase durations in blastomeres from vegetal hemispheres than those from animal hemispheres. Furthermore, upon recapitulating interphase events by manipulating the concentration of yolk platelets, which are originally rich in the vegetal blastomeres, in cell-free cytoplasmic extracts, there was slower nuclear expansion and DNA replication as compared to normal yolk-free conditions. Under these conditions, the supplemented yolk platelets accumulated around the nucleus in a microtubule-dependent manner and impeded organization of the endoplasmic reticulum network. Overall, we propose that yolk platelets around the nucleus reduce membrane supply from the endoplasmic reticulum to the nucleus, resulting in slower nuclear expansion in the yolk-rich vegetal blastomeres.

Homogeneous nucleation in a Poiseuille flow

Variation of the critical nucleus size and the corresponding work of formation with average flow speed at axisymmetric axis.

Megakaryocyte-Derived TGF-β1 Negatively Regulates Megakaryopoiesis in Mice

Megakaryocytes (MK) and platelets contain a high concentration of transforming growth factor β1 (TGFβ1). Mice with conditional deletion of Tgfb1 in megakaryocytes (PF4Cre/Tgfb1flox/flox) resulted in >90% reduction of TGFβ1 in platelets and 50% reduction of TGFβ1 in plasma. TGFβ1 has been shown to play an inhibitory role in megakaryopoiesis in vitro, and inhibiting TGFβ1 increased megakaryopoiesis in vivo. However, the source of TGFβ1 in megakaryopoiesis is unknown. In this study, we tested whether megakaryocyte-derived TGFβ1 contributes to megakaryopoiesis in bone marrow (BM) by comparing three groups of mice: PF4Cre/Tgfb1flox/flox, littermate control Tgfb1flox/flox, and WTC57Bl/6 mice. Bones (femurs) from these mice (n=12) (age 15-30 weeks, males 60% and females 40%) were harvested, fixed, decalcified, sectioned, and H&E stained. Whole stained BM areas of the sectioned femurs were scanned with an Aperio slide scanner to quantify the number of megakaryocytes and the demarcation membrane system (DMS) and ploidy (nucleus size) of the megakaryocytes were quantified by manually counting megakaryocytes and tracing their DMS and nucleus. The percentage of MK among total BM cells was calculated by dividing total numbers of BM cells in the total area of a BM section with the number of MK in the section. Freshly isolated BM cells were cultured in vitro in culture medium (DMEM+10%FBS) in the presence of thrombopoietin (TPO, 100 ng/ml) with and without TGFβ1 (20 ng/ml) or with a neutralized antibody against the active form of TGFβ1 (AF-101; 2 ug/ml). TGFβ1 and TPO levels in plasma, BM exudates, and cells were measured by ELISA. PF4Cre/Tgfb1flox/floxmice had >50% reduction in TGFβ1 levels in BM cells and exudates (TGFβ1 levels in BM exudates were 1.4 ± 0.033 ng in WT and 0.68 ± 0.065 ng in PF4CreTgfb1flox/floxmice, p<0.01; and in BM cells 50 ± 9 ng/ml in WT and 22 ± 4.2 ng/ml in PF4CreTgfb1flox/flox; p<0.001). MK numbers were ~25% higher in PF4Cre/Tgfb1flox/floxmice (n=6) compared to combined littermate controls (n=3) and WT (n=3) (MK was 0.30 ± 0.02% in PF4Cre/Tgfb1flox/flox and 0.23 ± 0.16% in combined controls; p<0.001 (n=6), whereas blood platelet counts were only marginally higher in PF4Cre/Tgfb1flox/flox (1114 ± 300) vs. controls (806 ± 116; p<0.05). There was a ~2-fold higher plasma TPO levels in PF4CreTgfb1flox/floxmice vs. WT (p=0.04, n=4). Increased DMS and nucleus areas in MK have been shown to correlate with proplatelets formation and platelet production. However, DMS and nuclear areas remained unchanged between genotypes [(DMS area was 197 ± 46 in PF4CreTgfb1flox/flox and 228 ± 50 um2 in combined WT and littermate controls (p=0.3), and nucleus size was 154 ± 23 in PF4CreTgfb1flox/flox and 160 ± 33 um2 in controls (p=0.7)], indicating that the role of TGFβ1 is limited to megakaryopoiesis. To test whether the in vivo phenotype was recapitulated, we cultured whole BM isolated from WT and PF4Cre/Tgfb1flox/flox mice, which showed a ~2.5-fold increase in MK numbers vs. WT when cultured for 5 days in TPO-supplemented medium. The addition of recombinant TGFβ1 in culture medium inhibited MK numbers, and a neutralizing antibody against TGFβ1 resulted in increased MK numbers. We conclude that MK-derived TGFβ1 negatively regulates megakaryopoiesis in mice. Further investigation is needed to determine the mechanism by which TGFβ1 regulates TPO-induced megakaryopoiesis. Our study may be important in megakaryocyte generation in vitro and may have important implications in vivo under normal and stress-inducing conditions where variable megakaryopoiesis is observed, such as essential thrombocythemia and primary myelofibrosis. Disclosures No relevant conflicts of interest to declare.