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1. Endoreduplication during embryogenesis in Megacyclops gigas (Crustacea: Cyclopoida): A rare example of depolyploidization

   Jordan, Kathryn; Sheveleva, Natalya; Hołyńska, Maria; Wyngaard, Grace A (February 2025, Invertebrate biology)

   Megacyclops gigas, a freshwater microcrustacean (Copepoda: Cyclopoida), undergoes endoreduplication during early embryogenesis, a process during which DNA synthesis during the cell cycle occurs without subsequent mitosis and cytokinesis. This kind of cell cycle, an endocycle, results in a doubling of the nuclear DNA content. By the 4-cell embryonic stage, two endocycles have occurred, increasing the initial 2C level of DNA at 7.5 pg DNA per nucleus to the 8C level at 30 pg DNA per nucleus. These 8C cells proliferate to produce additional cells at the 8C level in the 8-cell embryo. DNA contents were measured using Feulgen Image Analysis Densitometry. Re-entry into the typical 2C – 4C cell cycle has begun by the 6th cleavage division, with some cell lineages containing 2C amounts while others contain 4C amounts. This mixture of cells with different DNA contents persists until the ~ 500-cell stage. All adult somatic cells contain the 2C amount of DNA. Some half anaphase chromosome figures at the 64-cell stage contain ~ 5 or ~ 9 pg DNA per nucleus, indicative of aneuploidy resulting from imperfect mitoses. The large clutch sizes of M. gigas may compensate for such an error prone process. Endoreduplication of the kind found in M. gigas is rare in that (1) it involves endocycles in all cells of the organism in a particular developmental stage, rather than being limited to specific tissues and (2) the endoreduplicated cells undergo depolyploidization. Overall, genomic stability in the M. gigas population appears to be unaffected. We hypothesize that the role of endoreduplication in this species is associated with a combination of increased demands for cellular differentiation and protein transcription related to the unusually large body size of M. gigas and its habitat type characterized by extremely low temperatures. 

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2. Nucleolar dynamics and interactions with nucleoplasm in living cells

   https://doi.org/10.7554/eLife.47533  

   Caragine, Christina M; Haley, Shannon C; Zidovska, Alexandra (November 2019, eLife)

   The inside of a cell is very organized. Just as bodies contain internal organs, cells contain many different compartments, called ‘organelles’, each with its own specific role. Most organelles are surrounded by a membrane that keeps their contents separate from the cytoplasm, the water-based liquid inside the rest of the cell. Some organelles, however, are not bounded by a membrane. Instead, they act like tiny drops of oil in water, retaining their structure because they have different physical properties from the fluid around them, a phenomenon called liquid-liquid phase separation. One such organelle is the nucleolus, which sits inside the cell’s nucleus (a membrane-bound organelle containing all the genetic material of the cell in the form of DNA). The nucleolus’s job is to produce ribosomes, the cellular machines that, once transported out of the nucleus, will make proteins. Human cells start with 10 small nucleoli in the nucleus, which fuse together until only one or two larger ones remain. Previous research showed that nucleoli form and persist thanks to liquid-liquid phase separation, and they behave like liquid droplets. Despite this, exactly how nucleoli interact with each other and with the fluid environment in the rest of the nucleus remained unknown. Caragine et al. set out to measure the behavior and interactions of nucleoli in living human cells. Microscopy experiments using human cells grown in the laboratory allowed the positions, size and shape of nucleoli to be tracked over time. This also yielded detailed information about the smoothness of their surface. Mathematical analysis revealed that pairs of nucleoli normally moved independently of each other, unless they were about to fuse, when they invariably slowed down and coordinated their movements. In addition, altering the state of DNA in the surrounding nucleus also affected the nucleoli. For example, when DNA was less densely packed, nucleoli shrank and their surfaces became smoother. These results build on our knowledge of how cells are organized by showing, for the first time, that the environment within the nucleus directly shapes the behavior of nucleoli. In the future, a better understanding of how cells maintain healthy nucleoli may help develop new treatments for human diseases such as cancer, which are characterized by problems with this organelle. 

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3. Silica depleted rice hull ash (SDRHA), an agricultural waste, as a high-performance hybrid lithium-ion capacitor

   https://doi.org/10.1039/D0GC01746A  

   E. Temeche, M. Yu (July 2020, Green chemistry)

   null (Ed.)

   Rice hull ash (RHA, an agricultural waste) produced during combustion of rice hulls to generate electricity consists (following dilute acid leaching) of high surface area SiO2 (80–90 wt%) and 10–20 wt% carbon (80 m2 g−1 total). RHA SiO2 is easily extracted by distillation (spirosiloxane) producing SDRHA, which offers an opportunity to develop “green” hybrid lithium-ion capacitors (LICs) electrodes. SDRHA consists of 50–65 wt% SiO2 with the remainder carbon with a specific surface area of ≈220 m2 g−1. SDRHA microstructure presents a highly irregular and disordered nanocomposite composed of nanosilica closely connected via graphene layers enhancing Li-ion mobility during charge/discharge process. SDRHA electrochemicalproperties were assessed by assembling Li/SDRHA half-cells and LiNi0.6Co0.2Mn0.2O2 (NMC622)-SDRHA full-cells. The half-cell delivered a high specific capacity of 250 mA h g−1 at 0.5C and retained a capacity of 200 mA h g−1 at 2C for 400 h. In contrast to the poor cycle performance of NMC based batteries at high C-rates, the hybrid full-cell demonstrated a high specific capacitance of 200 F g−1 at 4C. In addition, both the half and full hybrid cells demonstrate excellent coulombic efficiencies (∼100%). These results suggest that low cost and environmentally friendly SDRHA, may serve as a potentialalternative electrode material for LICs. 

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4. Microfluidic single-cell measurements of oxidative stress as a function of cell cycle position

   https://doi.org/10.1007/s00216-023-04924-z  

   Allcroft, Tyler J; Duong, Jessica T; Skardal, Per Sebastian; Kovarik, Michelle L (November 2023, Analytical and Bioanalytical Chemistry)

   Single-cell measurements routinely demonstrate high levels of variation between cells, but fewer studies provide insight into the analytical and biological sources of this variation. This is particularly true of chemical cytometry, in which individual cells are lysed and their contents separated, compared to more established single-cell measurements of the genome and transcriptome. To characterize population level variation and its sources, we analyzed oxidative stress levels in 1278 individual Dictyostelium discoideum cells as a function of exogenous stress level and cell cycle position. Cells were exposed to varying levels of oxidative stress via singlet oxygen generation using the photosensitizer Rose Bengal. Single-cell data reproduced the dose-response observed in ensemble measurements by CE-LIF, superimposed with high levels of heterogeneity. Through experiments and data analysis, we explored possible biological sources of this heterogeneity. No trend was observed between population variation and oxidative stress level, but cell cycle position was a major contributor to heterogeneity in oxidative stress. Cells synchronized to the same stage of cell division were less heterogeneous than unsynchronized cells (RSD of 37-51% vs 93%), and mitotic cells had higher levels of reactive oxygen species than interphase cells. While past research has proposed changes in cell size during the cell cycle as a source of biological noise, the measurements presented here use an internal standard to normalize for effects of cell volume, suggesting that a more complex contribution of cell cycle in heterogeneity of oxidative stress. 

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5. Constricted migration increases DNA damage and independently represses cell cycle

   Pfeifer, C. (May 2018, Molecular biology of the cell)

   Cell migration through dense tissues or small capillaries can elongate the nucleus and even damage it, and any impact on cell cycle has the potential to affect various processes including carcinogenesis. Here, nuclear rupture and DNA damage increase with constricted migration in different phases of cell cycle-which we show is partially repressed. We study several cancer lines that are contact inhibited or not and that exhibit diverse frequencies of nuclear lamina rupture after migration through small pores. DNA repair factors invariably mislocalize after migration, and an excess of DNA damage is evident as pan-nucleoplasmic foci of phosphoactivated ATM and gamma H2AX. Foci counts are suppressed in late cell cycle as expected of mitotic checkpoints, and migration of contact-inhibited cells through large pores into sparse microenvironments leads also as expected to cell-cycle reentry and no effect on a basal level of damage foci. Constricting pores delay such reentry while excess foci occur independent of cell-cycle phase. Knockdown of repair factors increases DNA damage independent of cell cycle, consistent with effects of constricted migration. Because such migration causes DNA damage and impedes proliferation, it illustrates a cancer cell fate choice of "go or grow." 

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