Highlights d Pancreas tissue slices from surgical resections allow study of b cells in T2D d b cell dysfunction develops early and deteriorates further in T2D pathogenesis d Basal and first-phase insulin is altered in impaired glucosetolerant donor tissue d b cell mass in tissue slices appears intact throughout the progression to T2D

No abstract

Centrosomes must resist microtubule-mediated forces for mitotic chromosome segregation. During mitotic exit, however, centrosomes are deformed and fractured by those same forces, which is a key step in centrosome disassembly. How the functional material properties of centrosomes change throughout the cell cycle, and how they are molecularly tuned, remain unknown. Here, we used optically induced flow perturbations to determine the molecular basis of centrosome strength and ductility in C. elegans embryos. We found that both properties declined sharply at anaphase onset, long before natural disassembly. This mechanical transition required PP2A phosphatase and correlated with inactivation of PLK-1 (Polo kinase) and SPD-2 (Cep192). In vitro, PLK-1 and SPD-2 directly protected centrosome scaffolds from force-induced disassembly. Our results suggest that, before anaphase, PLK-1 and SPD-2 respectively confer strength and ductility to the centrosome scaffold so that it can resist microtubule-pulling forces. In anaphase, centrosomes lose PLK-1 and SPD-2 and transition to a weak, brittle state that enables force-mediated centrosome disassembly.

Centrosomes are microtubule-nucleating organelles that facilitate chromosome segregation and cell division in metazoans. Centrosomes comprise centrioles that organize a micron-scale mass of protein called pericentriolar material (PCM) from which microtubules nucleate. During each cell cycle, PCM accumulates around centrioles through phosphorylation-mediated assembly of PCM scaffold proteins. During mitotic exit, PCM swiftly disassembles by an unknown mechanism. Here, we used Caenorhabditis elegans embryos to determine the mechanism and importance of PCM disassembly in dividing cells. We found that the phosphatase PP2A and its regulatory subunit SUR-6 (PP2ASUR-6), together with cortically directed microtubule pulling forces, actively disassemble PCM. In embryos depleted of these activities, ∼25% of PCM persisted from one cell cycle into the next. Purified PP2ASUR-6 could dephosphorylate the major PCM scaffold protein SPD-5 in vitro. Our data suggest that PCM disassembly occurs through a combination of dephosphorylation of PCM components and force-driven fragmentation of the PCM scaffold.

Centrosomes are major microtubule-nucleating organelles that facilitate chromosome segregation and cell division in metazoans. Centrosomes comprise centrioles that organize a micron-scale mass of protein called pericentriolar material (PCM) from which microtubules nucleate. During each cell cycle, PCM accumulates around centrioles through phosphorylation-mediated assembly of PCM scaffold proteins. During mitotic exit, PCM swiftly disassembles by an unknown mechanism. Here, we used Caenorhabditis elegans embryos to determine the mechanism and importance of PCM disassembly in dividing cells. We found that the phosphatase PP2A and its regulatory subunit SUR-6 (PP2A ), together with cortically directed microtubule pulling forces, actively disassemble PCM. In embryos depleted of these activities, ~25% of PCM persisted from one cell cycle into the next, resulting in cytokinetic furrow ingression errors, excessive centrosome accumulation, and embryonic death. Purified PP2A could dephosphorylate the major PCM scaffold protein SPD-5 in vitro. Our data suggest that PCM disassembly occurs through a combination of dephosphorylation of PCM components and catastrophic rupture of the PCM scaffold.

14

Gene expression is partly controlled by posttranscriptional modifications to histones. These modifications either loosen the binding between histones and DNA, allowing for transcription, or tighten the binding, which prevents transcription. Histone acetyltransferases (HATs) are responsible for histone acetylation, while histone deacetylases (HDACs) remove acetyl groups and are involved in gene silencing. HDAC activity is often upregulated in cancer cells, leading to the repression of several genes that normally prevent tumor formation. Due to the role of HDACs in cancer development and progression, HDAC inhibitors (HDACi) are promising treatments for several cancers. Furthermore, unlike many traditional chemotherapeutics, HDACi appear to have limited effect on normal cell growth and function.Cyclic, cysteine‐containing, depsipeptides are a promising class of HDACi. These HDACi require three major characteristics: a Lewis basic group that associates with the Zn2+ ion at the heart of the active site, a cyclic region that binds to the nonpolar amino acid residues at the rim of the active site channel, and a linker of four to seven atoms that connects the nonpolar region to the Lewis basic group, presumably mimicking the structure of lysine. We tested four analogs with altered cyclic regions.An MTT assay was used to measure cytotoxicity induced by each depsipetide on the histoiocytic lymphoma cell line, U937. Depsipeptides that were cytotoxic were investigated for their ability to induce apoptosis using a CaspACETM Assay. Most effective novel depsipeptides were those with smaller, nonpolar cyclic regions.