Quantification of silver nanoparticle interactions with yeast Saccharomyces cerevisiae studied using single-cell ICP-MS.

Silver nanoparticles (AgNPs) have been used in many fields due to their anticancer, antimicrobial, and antiviral potential. Single-cell ICP-MS (SC-ICP-MS) is an emerging technology that allows for the rapid characterization and quantification of a metal analyte across a cell population in a single analysis. In this study, a new rapid and sensitive SC-ICP-MS method was developed to quantitatively study the interactions of AgNPs with yeast Saccharomyces cerevisiae.

Staining of the Actin Cytoskeleton During Cell Division in Budding Yeast and Mammalian Cells.

Observation of actin at the cortex in dividing cells can be accomplished using the fungal toxin phalloidin conjugated to fluorophores. Protocols for staining both budding yeast and cultured mammalian cells with fluorescent phalloidin are described. This technique can be combined with immunofluorescence to image actin filaments and other proteins involved in cell division simultaneously.

Student Preclass Preparation by Both Reading the Textbook and Watching Videos Online Improves Exam Performance in a Partially Flipped Course.

The flipped classroom has the potential to improve student performance. Because flipping involves both preclass preparation and problem solving in the classroom, the means by which increased learning occurs and whether the method of delivering content matters is of interest. In a partially flipped cell biology course, students were assigned online videos before the flipped class and textbook reading before lectures.

Dephosphorylation of Iqg1 by Cdc14 regulates cytokinesis in budding yeast.

Cytokinesis separates cells by contraction of a ring composed of filamentous actin (F-actin) and type II myosin. Iqg1, an IQGAP family member, is an essential protein in Saccharomyces cerevisiae required for assembly and contraction of the actomyosin ring. Localization of F-actin to the ring occurs only after anaphase and is mediated by the calponin homology domain (CHD) of Iqg1, but the regulatory mechanisms that temporally restrict actin ring assembly are not well defined.

Mutation of Hof1 PEST motif phosphorylation sites leads to retention of Hof1 at the bud neck and a decrease in the rate of myosin contraction.

Regulation of actomyosin ring contraction is important for the coordination of cytokinesis with mitosis. Hof1, a member of the Pombe Cdc15 homology (PCH) family of proteins, is required for efficient cytokinesis in budding yeast. Phosphorylation of Hof1 depends on the mitotic exit network (MEN), and its degradation at the end of mitosis depends on its PEST motif and interaction with the E3 ligase Grr1.

IQGAP Family Members in Yeast, Dictyostelium, and Mammalian Cells.

IQGAPs are a family of scaffolding proteins with multiple domains, named for the IQ motifs and GTPase activating protein (GAP) related domains. Despite their GAP homology, IQGAP proteins act as effectors for GTP-bound GTPases of the Ras superfamily and do not stimulate GTP hydrolysis. IQGAPs are found in eukaryotic cells from yeast to human, and localize to actin-containing structures such as lamellipodia, membrane ruffles, cell-cell adhesions, phagocytic cups, and the actomyosin ring formed during cytokinesis.

Cellular internalization of quantum dots noncovalently conjugated with arginine-rich cell-penetrating peptides.

Protein transduction domains comprised of basic amino acid-rich peptides, can efficiently deliver covalently fused macromolecules into cells. Quantum dots (QDs) are luminescent semiconductor nanocrystals that are finding increasing application in biological imaging. Previous studies showed that protein transduction domains mediate the internalization of covalently attached QDs.

Nona-arginine facilitates delivery of quantum dots into cells via multiple pathways.

Semiconductor quantum dots (QDs) have recently been used to deliver and monitor biomolecules, such as drugs and proteins. However, QDs alone have a low efficiency of transport across the plasma membrane. In order to increase the efficiency, we used synthetic nona-arginine (SR9), a cell-penetrating peptide, to facilitate uptake.

Study of uptake and loss of silica nanoparticles in living human lung epithelial cells at single cell level.

The toxicology of nanomaterials is a blooming field of study, yet it is difficult to keep pace with the innovations in new materials and material applications. Those applications are quickly being introduced in research, industrial, and consumer settings. Even though the cytotoxicity of many types of nanoparticles has been demonstrated, the behavior of those particles in a biological environment is not yet fully known.

The mechanism of elevated toxicity in HepG2 cells due to combined exposure to ethanol and ionizing radiation.

Ethanol and ionizing radiation exposure are independently known to cause tissue damage through various mechanisms. The non-enzymatic and enzymatic metabolism of ethanol, the latter via the cytochrome P(450) 2E1-dependent pathway produces free radicals, which deplete cellular glutathione (GSH). Ionizing radiation exposure has been shown to induce lipid peroxidation, DNA damage, protein oxidation and GSH depletion.

Taxol-stabilized microtubules can position the cytokinetic furrow in mammalian cells.

How microtubules act to position the plane of cell division during cytokinesis is a topic of much debate. Recently, we showed that a subpopulation of stable microtubules extends past chromosomes and interacts with the cell cortex at the site of furrowing, suggesting that these stabilized microtubules may stimulate contractility. To test the hypothesis that stable microtubules can position furrows, we used taxol to rapidly suppress microtubule dynamics during various stages of mitosis in PtK1 cells.

Mad2 and BubR1 function in a single checkpoint pathway that responds to a loss of tension.

The spindle checkpoint monitors microtubule attachment and tension at kinetochores to ensure proper chromosome segregation. Previously, PtK1 cells in hypothermic conditions (23 degrees C) were shown to have a pronounced mitotic delay, despite having normal numbers of kinetochore microtubules. At 23 degrees C, we found that PtK1 cells remained in metaphase for an average of 101 min, compared with 21 min for cells at 37 degrees C.

Anaphase onset does not require the microtubule-dependent depletion of kinetochore and centromere-binding proteins.

Spindle checkpoint proteins, such as Mad2 and BubR1, and the motors dynein/dynactin and CENP-E usually leave kinetochores prior to anaphase onset by microtubule-dependent mechanisms. Likewise, 'chromosome passenger proteins' including INCENP are depleted from the centromeres after anaphase onset and then move to the midzone complex, an event that is essential for cytokinesis. Here we test whether the cell cycle changes that occur at anaphase onset require or contribute to the depletion of kinetochore and centromere proteins independent of microtubules.

Chromosome dynamics: new light on Aurora B kinase function.

Aurora B family kinases play an essential role in chromosome segregation and cytokinesis. Recent work suggests that the kinase activity is required for bipolar chromosome orientation, kinetochore assembly, spindle checkpoint and microtubule dynamics. Aurora B also has additional functions in chromosome condensation and cohesion.