Particle-based model of cellular morphogenesis in budding yeast

We apply Lagrangian particle method combined with the level-set method to model morphogenesis of budding yeast on the subcellular level. We model the biochemical reactions, anisotropic diffusion, membrane-cytoplasmic transport of proteins and introduction of new membrane material (exocytosis) that occur on the plasma membrane. Exocytosis results in protrusion of the membrane surface. Hence, to model these phenomena we need to solve a system of reaction-diffusion-advection equations on the evolving surface

Identification of Novel, Evolutionarily Conserved Cdc42p-interacting Proteins and of Redundant Pathways Linking Cdc24p and Cdc42p to Actin Polarization in Yeast

In the yeast Saccharomyces cerevisiae, Cdc24p functions at least in part as a guanine-nucleotide-exchange factor for the Rho-family GTPase Cdc42p. A genetic screen designed to identify possible additional targets of Cdc24p instead identified two previously known genes, MSB1 and CLA4, and one novel gene, designated MSB3, all of which appear to function in the Cdc24p–Cdc42p pathway. Nonetheless, genetic evidence suggests that Cdc24p may have a function that is distinct from its Cdc42p guanine-nucleotide-exchange factor activity; in particular, overexpression of CDC42 in combination with MSB1 or a truncated CLA4 in cells depleted for Cdc24p allowed polarization of the actin cytoskeleton and polarized cell growth, but not successful cell proliferation. MSB3 has a close homologue (designated MSB4) and two more distant homologues (MDR1 and YPL249C) in S. cerevisiae and also has homologues in Schizosaccharomyces pombe, Drosophila (pollux), and humans (the oncogene tre17). Deletion of either MSB3 or MSB4 alone did not produce any obvious phenotype, and the msb3 msb4 double mutant was viable. However, the double mutant grew slowly and had a partial disorganization of the actin cytoskeleton, but not of the septins, in a fraction of cells that were larger and rounder than normal. Like Cdc42p, both Msb3p and Msb4p localized to the presumptive bud site, the bud tip, and the mother-bud neck, and this localization was Cdc42p dependent. Taken together, the data suggest that Msb3p and Msb4p may function redundantly downstream of Cdc42p, specifically in a pathway leading to actin organization. From previous work, the BNI1, GIC1, and GIC2 gene products also appear to be involved in linking Cdc42p to the actin cytoskeleton. Synthetic lethality and multicopy suppression analyses among these genes, MSB, and MSB4, suggest that the linkage is accomplished by two parallel pathways, one involving Msb3p, Msb4p, and Bni1p, and the other involving Gic1p and Gic2p. The former pathway appears to be more important in diploids and at low temperatures, whereas the latter pathway appears to be more important in haploids and at high temperatures

Particle-based model of cellular morphogenesis in budding yeast

We apply Lagrangian particle method combined with the level-set method to model morphogenesis of budding yeast on the subcellular level. We model the biochemical reactions, anisotropic diffusion, membrane-cytoplasmic transport of proteins and introduction of new membrane material (exocytosis) that occur on the plasma membrane. Exocytosis results in protrusion of the membrane surface. Hence, to model these phenomena we need to solve a system of reaction-diffusion-advection equations on the evolving surface

Identification of Novel, Evolutionarily Conserved Cdc42p-interacting Proteins and of Redundant Pathways Linking Cdc24p and Cdc42p to Actin Polarization in Yeast

In the yeast Saccharomyces cerevisiae, Cdc24p functions at least in part as a guanine-nucleotide-exchange factor for the Rho-family GTPase Cdc42p. A genetic screen designed to identify possible additional targets of Cdc24p instead identified two previously known genes, MSB1 and CLA4, and one novel gene, designated MSB3, all of which appear to function in the Cdc24p–Cdc42p pathway. Nonetheless, genetic evidence suggests that Cdc24p may have a function that is distinct from its Cdc42p guanine-nucleotide-exchange factor activity; in particular, overexpression of CDC42 in combination with MSB1 or a truncated CLA4 in cells depleted for Cdc24p allowed polarization of the actin cytoskeleton and polarized cell growth, but not successful cell proliferation. MSB3 has a close homologue (designated MSB4) and two more distant homologues (MDR1 and YPL249C) in S. cerevisiae and also has homologues in Schizosaccharomyces pombe, Drosophila (pollux), and humans (the oncogene tre17). Deletion of either MSB3 or MSB4 alone did not produce any obvious phenotype, and the msb3 msb4 double mutant was viable. However, the double mutant grew slowly and had a partial disorganization of the actin cytoskeleton, but not of the septins, in a fraction of cells that were larger and rounder than normal. Like Cdc42p, both Msb3p and Msb4p localized to the presumptive bud site, the bud tip, and the mother-bud neck, and this localization was Cdc42p dependent. Taken together, the data suggest that Msb3p and Msb4p may function redundantly downstream of Cdc42p, specifically in a pathway leading to actin organization. From previous work, the BNI1, GIC1, and GIC2 gene products also appear to be involved in linking Cdc42p to the actin cytoskeleton. Synthetic lethality and multicopy suppression analyses among these genes, MSB, and MSB4, suggest that the linkage is accomplished by two parallel pathways, one involving Msb3p, Msb4p, and Bni1p, and the other involving Gic1p and Gic2p. The former pathway appears to be more important in diploids and at low temperatures, whereas the latter pathway appears to be more important in haploids and at high temperatures

The yeast endocytic protein Epsin 2 functions in a cell-division signaling pathway

The epsins are a family of adaptors involved in recruiting other endocytic proteins, binding of ubiquitylated cargo and induction of membrane curvature. These molecules bear a characteristic epsin N-terminal homology (ENTH) domain and multiple peptide motifs that mediate protein-protein interactions. We have previously demonstrated that the ENTH domain of epsin is involved in Cdc42 signaling regulation. Here, we present evidence that yeast epsin 2 (Ent2) plays a signaling role during cell division. We observed that overexpression of the ENTH domain of Ent2 (ENTH2), but not Ent1, promoted the formation of chains of cells and aberrant septa. This dominant-negative effect resulted from ENTH2-mediated interference with septin assembly pathways. We mapped the ENTH2 determinants responsible for induction of the phenotype and found them to be important for efficient binding to the septin regulatory protein, Bem3. Supporting a physiological role for epsin 2 in cell division, the protein localized to sites of polarized growth and cytokinesis and rescued a defect in cell division induced by Bem3 misregulation. Collectively, our findings provide a potential molecular mechanism linking endocytosis (via epsin 2) with signaling pathways regulating cell division

Lipocalin-2 induces NLRP3 inflammasome activation via HMGB1 induced TLR4 signaling in heart tissue of mice under pressure overload challenge

Lipocalin-2 (also known as NGAL) levels are elevated in obesity and diabetes yet relatively little is known regarding effects on the heart. We induced pressure overload (PO) in mice and found that lipocalin-2 knockout (LKO) mice exhibited less PO-induced autophagy and NLRP3 inflammasome activation than Wt. PO-induced mitochondrial damage was reduced and autophagic flux greater in LKO mice, which correlated with less cardiac dysfunction. All of these observations were negated upon adenoviral-mediated restoration of normal lipocalin-2 levels in LKO. Studies in primary cardiac fibroblasts indicated that lipocalin-2 enhanced priming and activation of NLRP3-inflammasome, detected by increased IL-1β, IL-18 and Caspase-1 activation. This was attenuated in cells isolated from NLRP3-deficient mice or upon pharmacological inhibition of NLRP3. Furthermore, lipocalin-2 induced release of HMGB1 from cells and NLRP3-inflammasome activation was attenuated by TLR4 inhibition. We also found evidence of increased inflammasome activation and reduced autophagy in cardiac biopsy samples from heart failure patients. Overall, this study provides new mechanistic insight on the detrimental role of lipocalin-2 in the development of cardiac dysfunction