Secreted Endothelial Cell Factors Immobilized on Collagen Scaffolds Enhance the Recipient Endothelial Cell Environment.

Strategies to design novel vascular scaffolds are a continuing aim in tissue engineering and often such designs encompass the use of recombinant factors to enhance the performance of the scaffold. The established use of cell secretion utilized in feeder systems and conditioned media offer a source of paracrine factors, which has potential to be used in tissue-engineered (TE) scaffolds. Here we utilize this principle from endothelial cells (ECs), to create a novel TE scaffold by harnessing secreted factors and immobilizing these to collagen scaffolds. This research revealed increased cellular attachment and positive angiogenic gene upregulation responses in recipient ECs grown on these conditioned scaffolds. Also, the conditioning method did not affect the mechanical structural integrity of the scaffolds. These results may advocate the potential use of this system to improve vascular scaffolds' in vivo performance. In addition, this process may be a future method utilized to improve other tissue engineering scaffold therapies.

Munc18-1 protein molecules move between membrane molecular depots distinct from vesicle docking sites.

Four evolutionarily conserved proteins are required for mammalian regulated exocytosis: three SNARE proteins, syntaxin, SNAP-25, and synaptobrevin, and the SM protein, Munc18-1. Here, using single-molecule imaging, we measured the spatial distribution of large cohorts of single Munc18-1 molecules correlated with the positions of single secretory vesicles in a functionally rescued Munc18-1-null cellular model. Munc18-1 molecules were nonrandomly distributed across the plasma membrane in a manner not directed by mode of interaction with syntaxin1, with a small mean number of molecules observed to reside under membrane resident vesicles. Surprisingly, we found that the majority of vesicles in fully secretion-competent cells had no Munc18-1 associated within distances relevant to plasma membrane-vesicle SNARE interactions. Live cell imaging of Munc18-1 molecule dynamics revealed that the density of Munc18-1 molecules at the plasma membrane anticorrelated with molecular speed, with single Munc18-1 molecules displaying directed motion between membrane hotspots enriched in syntaxin1a. Our findings demonstrate that Munc18-1 molecules move between membrane depots distinct from vesicle morphological docking sites.

Global chromatin fibre compaction in response to DNA damage.

DNA is protected by packaging it into higher order chromatin fibres, but this can impede nuclear processes like DNA repair. Despite considerable research into the factors required for signalling and repairing DNA damage, it is unclear if there are concomitant changes in global chromatin fibre structure. In human cells DNA double strand break (DSB) formation triggers a signalling cascade resulting in H2AX phosphorylation (γH2AX), the rapid recruitment of chromatin associated proteins and the subsequent repair of damaged sites. KAP1 is a transcriptional corepressor and in HCT116 cells we found that after DSB formation by chemicals or ionising radiation there was a wave of, predominantly ATM dependent, KAP1 phosphorylation. Both KAP1 and phosphorylated KAP1 were readily extracted from cells indicating they do not have a structural role and γH2AX was extracted in soluble chromatin indicating that sites of damage are not attached to an underlying structural matrix. After DSB formation we did not find a concomitant change in the sensitivity of chromatin fibres to micrococcal nuclease digestion. Therefore to directly investigate higher order chromatin fibre structures we used a biophysical sedimentation technique based on sucrose gradient centrifugation to compare the conformation of chromatin fibres isolated from cells before and after DNA DSB formation. After damage we found global chromatin fibre compaction, accompanied by rapid linker histone dephosphorylation, consistent with fibres being more regularly folded or fibre deformation being stabilized by linker histones. We suggest that following DSB formation, although there is localised chromatin unfolding to facilitate repair, the bulk genome becomes rapidly compacted protecting cells from further damage.

Analysis of active and inactive X chromosome architecture reveals the independent organization of 30 nm and large-scale chromatin structures.

Using a genetic model, we present a high-resolution chromatin fiber analysis of transcriptionally active (Xa) and inactive (Xi) X chromosomes packaged into euchromatin and facultative heterochromatin. Our results show that gene promoters have an open chromatin structure that is enhanced upon transcriptional activation but the Xa and the Xi have similar overall 30 nm chromatin fiber structures. Therefore, the formation of facultative heterochromatin is dependent on factors that act at a level above the 30 nm fiber and transcription does not alter bulk chromatin fiber structures. However, large-scale chromatin structures on Xa are decondensed compared with the Xi and transcription inhibition is sufficient to promote large-scale chromatin compaction. We show a link between transcription and large-scale chromatin packaging independent of the bulk 30 nm chromatin fiber and propose that transcription, not the global compaction of 30 nm chromatin fibers, determines the cytological appearance of large-scale chromatin structures.