β2-Syntrophin is a Cdk5 substrate that restrains the motility of insulin secretory granules

The molecular basis for the interaction of insulin granules with the cortical cytoskeleton of pancreatic β-cells remains unknown. We have proposed that binding of the granule protein ICA512 to the PDZ domain of β2-syntrophin anchors granules to actin filaments and that the phosphorylation/dephosphorylation of β2-syntrophin regulates this association. Here we tested this hypothesis by analyzing INS-1 cells expressing GFP-β2-syntrophin through the combined use of biochemical approaches, imaging studies by confocal and total internal reflection fluorescence microscopy as well as electron microscopy. Our results support the notion that β2-syntrophin restrains the mobility of cortical granules in insulinoma INS-1 cells, thereby reducing insulin secretion and increasing insulin stores in resting cells, while increasing insulin release upon stimulation. Using mass spectrometry, in vitro phosphorylation assays and β2-syntrophin phosphomutants we found that phosphorylation of β2-syntrophin on S75 near the PDZ domain decreases its binding to ICA512 and correlates with increased granule motility, while phosphorylation of S90 has opposite effects. We further show that Cdk5, which regulates insulin secretion, phosphorylates S75. These findings provide mechanistic insight into how stimulation displaces insulin granules from cortical actin, thus promoting their motility and exocytosis.     

The importance of monkey beetle (Scarabaeidae: Hopliini) pollination for Aizoaceae and Asteraceae in grazed and ungrazed areas at Paulshoek, Succulent Karoo, South Africa

The relative importance of monkey beetles (Hopliini, Scarabeidae) as pollinators of Asteraceae and Aizoaceae in the Succulent Karoo as well as the influence of livestock grazing on their abundance and diversity was investigated. Hopliine beetles proved to be the, or among the, most abundant flower visitors of 12 investigated plant species. However, during single flower observations at three Aizoaceae species, bees (Apoidea), bee flies (Bombyliidae) and pollen wasps (Masaridae) were the most frequent flower visitors. However, monkey beetles carried the highest Asteraceae and Aizoaceae pollen loads, and are therefore considered to play a vital role in the pollination of these two families. Abundance, species richness and diversity of Hopliini did not appear to be heavily affected by livestock grazing. Annual variation in the composition of monkey beetle populations was more dramatic. Still, some species showed higher abundances on heavily grazed rangeland while others only occurred under low grazing pressure. It is presumed that changes in the composition of the vegetation, especially the observed decrease of perennial plants in favour of annuals and geophytes (Todd and Hoffman 1999) could in turn affect the composition of monkey beetle assemblages.     

p38 MAPK signaling pathway is involved in butyrate-induced vitamin D receptor expression

Previously, we have demonstrated that the butyrate-induced differentiation in the human colon cancer cell line Caco-2 occurs via upregulation of the vitamin D receptor (VDR). However, the downstream pathways involved are unknown. The mitogen-activated protein kinases (MAPKs) have been shown to play an important role in regulation of cell differentiation, and may therefore be a potential target of butyrate action. To assess their role in butyrate-mediated cell differentiation and VDR expression, we used the specific p38-MAPK inhibitor SB203580 and the ERK1/2 MAPK-inhibitor PD98059. The p38-MAPK inhibitor abolished the butyrate effect on VDR expression and cell differentiation, while the ERK1/2 inhibitor did not influence the butyrate-mediated induction of cell differentiation and VDR expression. The essential role of the p38 pathway in up-regulation of VDR expression was further confirmed by using the p38 stimulator arsenite. These results imply an important role of the p38-MAPK in regulation of cellular differentiation through upregulation of VDR expression by butyrate.     

Transposition and targeting of the prokaryotic mobile element IS30 in zebrafish

We provide evidence that a prokaryotic insertion sequence (IS) element is active in a vertebrate system. The transposase of Escherichia coli element IS30 catalyzes both excision and integration in extrachromosomal DNA in zebrafish embryos. The transposase has a pronounced target preference, which is shown to be modified by fusing the enzyme to unrelated DNA binding proteins. Joining the transposase to the cI repressor of phage λ causes transposition primarily into the vicinity of the λ operator in E. coli, and linking to the DNA binding domain of Gli1 also directs the recombination activity of transposase near to the Gli1 binding site in zebrafish. Our results demonstrate the possibility of fusion transposases to acquire novel target specificity in both prokaryotes and eukaryotes.     

Extended base pair complementarity between U1 snRNA and the 5' splice site does not inhibit splicing in higher eukaryotes, but rather increases 5' splice site recognition

Spliceosome formation is initiated by the recognition of the 5′ splice site through formation of an RNA duplex between the 5′ splice site and U1 snRNA. We have previously shown that RNA duplex formation between U1 snRNA and the 5′ splice site can protect pre-mRNAs from degradation prior to splicing. This initial RNA duplex must be disrupted to expose the 5′ splice site sequence for base pairing with U6 snRNA and to form the active spliceosome. Here, we investigated whether hyperstabilization of the U1 snRNA/5′ splice site duplex interferes with splicing efficiency in human cell lines or nuclear extracts. Unlike observations in Saccharomyces cerevisiae, we demonstrate that an extended U1 snRNA/5′ splice site interaction does not decrease splicing efficiency, but rather increases 5′ splice site recognition and exon inclusion. However, low complementarity of the 5′ splice site to U1 snRNA significantly increases exon skipping and RNA degradation. Although the splicing mechanisms are conserved between human and S.cerevisiae, these results demonstrate that distinct differences exist in the activation of the spliceosome.     

In vivo haematopoietic activity is induced in neurosphere cells by chromatin-modifying agents

Modifications of DNA and chromatin are fundamental for the establishment and maintenance of cell type-specific gene expression patterns that constitute cellular identities. To test whether the developmental potential of fetal brain-derived cells that form floating sphere colonies (neurospheres) can be modified by destabilizing their epigenotype, neurosphere cells were treated with chemical compounds that alter the acetylation and methylation patterns of chromatin and DNA. Intravenous infusion of bulk or clonally derived neurosphere cells treated with a combination of trichostatin A (TSA) plus 5-aza-2'-deoxycytidine (AzaC) (TSA/AzaC neurosphere cells) yielded long-term, multilineage and transplantable neurosphere-derived haematopoietic repopulation. Untreated neurosphere cells exhibited no haematopoietic repopulation activity. The neurosphere-derived haematopoietic cells showed a diploid karyotype, indicating that they are unlikely to be products of cell fusion events, a conclusion strengthened by multicolour fluorescence in situ hybridization. Our results indicate that altering the epigenotype of neurosphere cells followed by transplantation enables the generation of neurosphere-derived haematopoietic cells.     

Optical Absorption‐Based In Situ Characterization of Halide Perovskites

Halide perovskites have emerged as materials for high‐performance optoelectronic devices. Often, progress made to date in terms of higher efficiency and stability is based on increasing material complexity, i.e., formation of multicomponent halide perovskites with multiple cations and anions. In this review article, the use of in situ optical methods, namely, photoluminescence (PL) and UV‐vis, that provide access to the relevant time and length scales to ascertain chemistry–property relationships by monitoring evolving properties is discussed. Additionally, because halide perovskites are electron/ion conductors and prone to solid‐state ion transport under various external stimuli, application of these optical methods in the context of ionic movement is described to reveal mechanistic insights. Finally, examples of using in situ PL and UV‐vis to study degradation and phase transitions are reviewed to demonstrate the wealth of information that can be obtained regarding many different aspects of ongoing research activities in the field of halide perovskites.     

Nectar Sugar Production across Floral Phases in the Gynodioecious Protandrous Plant Geranium sylvaticum

Many zoophilous plants attract their pollinators by offering nectar as a reward. In gynodioecious plants (i.e. populations are composed of female and hermaphrodite individuals) nectar production has been repeatedly reported to be larger in hermaphrodite compared to female flowers even though nectar production across the different floral phases in dichogamous plants (i.e. plants with time separation of pollen dispersal and stigma receptivity) has rarely been examined. In this study, sugar production in nectar standing crop and secretion rate were investigated in Geranium sylvaticum, a gynodioecious plant species with protandry (i.e. with hermaphrodite flowers releasing their pollen before the stigma is receptive). We found that flowers from hermaphrodites produced more nectar than female flowers in terms of total nectar sugar content. In addition, differences in nectar production among floral phases were found in hermaphrodite flowers but not in female flowers. In hermaphrodite flowers, maximum sugar content coincided with pollen presentation and declined slightly towards the female phase, indicating nectar reabsorption, whereas in female flowers sugar content did not differ between the floral phases. These differences in floral reward are discussed in relation to visitation patterns by pollinators and seed production in this species.