High-resolution mapping of heterochromatin redistribution in a <it>Drosophila </it>position-effect variegation model

Abstract Background Position-effect variegation (PEV) is the stochastic transcriptional silencing of a gene positioned adjacent to heterochromatin. white-mottled X-chromosomal inversions in Drosophila are classic PEV models that show variegation of the eye color gene white due to its relocation next to pericentric heterochromatin. It has been suggested that in these models the spreading of heterochromatin across the rearrangement breakpoint causes the silencing of white. However, the extent of this spreading and the precise pattern of heterochromatin redistribution have remained unclear. To obtain insight into the mechanism of PEV, we constructed high-resolution binding maps of Heterochromatin Protein 1 (HP1) on white-mottled chromosomes. Results We find that HP1 invades euchromatin across the inversion breakpoints over ~175 kb and ~30 kb, causing de novo association of HP1 with 20 genes. However, HP1 binding levels in these regions show substantial local variation, and white is the most strongly bound gene. Remarkably, white is also the only gene that is detectably repressed by heterochromatin. Furthermore, we find that HP1 binding to the invaded region is particularly sensitive to the dosage of the histone methyltransferase Su(var)3-9, indicating that the de novo formed heterochromatin is less stable than naturally occurring constitutive heterochromatin. Conclusion Our molecular maps demonstrate that heterochromatin can invade a normally euchromatic region, yet the strength of HP1 binding and effects on gene expression are highly dependent on local context. Our data suggest that the white gene has an unusual intrinsic affinity for heterochromatin, which may cause this gene to be more sensitive to PEV than most other genes.</p

The presence of tissue renin-angiotensin system components in human burn wounds and scars

Objective: Healing of severe and large surface burn wounds is faced with hurdles such as aberrant wound healing and excessive scar formation. The tissue renin-angiotensin system (tRAS) is involved in dermal wound healing, and fibrosis of other organs. However, little is known about the presence of tRAS during burn wound healing in human skin. This study investigated the presence of tRAS components in human burn wounds and scars. Methods: Dermal tissue biopsies were collected from 39 patients and divided into six categories: burn wounds post burn day (PBD)0–9, PBD11–21 and PBD22–37; young scars (1.5–3.5 months), mature scars (>12 months) and control skin from 9 patients. The tRAS components angiotensin converting enzyme (ACE), chymase, angiotensin receptor 1 (AT1) and Mas receptor were detected via immunohistochemistry. Digital images were acquired and analyzed using image analysis software. Results: Burn wounds from PBD22–37 showed a decreased expression of ACE and chymase compared to earlier time points or control, respectively. In contrast, ACE expression was increased in young scars compared to control skin but was normalized in mature scars. In comparison to control, mature scars showed increased AT1 expression. Conclusions: These results show the presence of components of tRAS in human burn wounds and scars. In addition, they suggest that tRAS has a time-dependent response during burn wound healing. Reduced tRAS might play a role in delayed healing, while an increase during remodeling phase might contribute to scar formation. This research provides a basis for future studies exploring tRAS involvement in burn wounds and scars. Keywords: Tissue renin-angiotensin system, Burn wounds, Scars, Ski

Different properties of skin of different body sites: The root of keloid formation?

The purpose of this study was to examine extracellular matrix composition, vascularization, and immune cell population of skin sites prone to keloid formation. Keloids remain a complex problem, posing esthetical as well as functional difficulties for those affected. These scars tend to develop at anatomic sites of preference. Mechanical properties of skin vary with anatomic location and depend largely on extracellular matrix composition. These differences in extracellular matrix composition, but also vascularization and resident immune cell populations might play a role in the mechanism of keloid formation. To examine this hypothesis, skin samples of several anatomic locations were taken from 24 human donors within zero to 36 hours after they had deceased. Collagen content and cross-links were determined through high-performance liquid chromatography. The expression of several genes, involved in extracellular matrix production and degradation, was measured by means of real-time PCR. (Immuno)histochemistry was performed to detect fibroblasts, collagen, elastin, blood vessels, Langerhans cells, and macrophages. Properties of skin of keloid predilections sites were compared to properties of skin from other locations (nonpredilection sites [NPS]). The results indicated that there are site specific variations in extracellular matrix properties (collagen and cross-links) as well as macrophage numbers. Moreover, predilection sites (PS) for keloid formation contain larger amounts of collagen compared to NPS, but decreased numbers of macrophages, in particular classically activated CD40 positive macrophages. In conclusion, the altered (histological, protein, and genetic) properties of skin of keloid PS may cause a predisposition for and contribute to keloid formation

Inhibited early immunologic response is associated with hypertrophic scarring

This study aimed to examine changes in the inflammatory response in early hypertrophic compared to normal wound healing. The immune system is thought to be involved in hypertrophic scar formation. However, the exact mechanism and time of onset of the derailment remain unknown. In a prospective observational study, skin biopsies were taken directly postwounding and 3 hours later from patients who had elective cardiothoracic surgery. The skin biopsies were analysed for mRNA, proteins and cells involved in the early inflammatory phase of wound healing. The endpoint was scar outcome (hypertrophic (HTS) or normal (NTS)) at one year after surgery. There were significant differences between the NTS and HTS groups regarding the fold changes of mRNA expression of P-selectin during surgery. Postoperative skin concentrations of inflammatory proteins IL-6, IL-8 and CCL2 were significantly lower in the HTS compared to the NTS group. Also, a trend of higher pre-operative M2 macrophage numbers was observed in the HTS group. Neutrophil numbers increased equally during surgery in both groups. The increase of P-selectin mRNA in hypertrophic wound healing could affect leucocyte migration. The decreased concentrations of inflammatory proteins in hypertrophic wound healing indicate a reduced inflammatory response, which has consequences for the treatment of hypertrophic scarring during the early inflammatory phase. In a conclusion, alterations of wound healing associated with hypertrophic scarring are visible as early as 3 hours postwounding and include a reduced rather than increased inflammatory protein response

Domain organization of human chromosomes revealed by mapping of nuclear lamina interactions

The architecture of human chromosomes in interphase nuclei is still largely unknown. Microscopy studies have indicated that specific regions of chromosomes are located in close proximity to the nuclear lamina (NL)(1-3). This has led to the idea that certain genomic elements may be attached to the NL, which may contribute to the spatial organization of chromosomes inside the nucleus. However, sequences in the human genome that interact with the NL in vivo have not been identified. Here we construct a high-resolution map of the interaction sites of the entire genome with NL components in human fibroblasts. This map shows that genome - lamina interactions occur through more than 1,300 sharply defined large domains 0.1 - 10 megabases in size. These lamina-associated domains ( LADs) are typified by low gene- expression levels, indicating that LADs represent a repressive chromatin environment. The borders of LADs are demarcated by the insulator protein CTCF, by promoters that are oriented away from LADs, or by CpG islands, suggesting possible mechanisms of LAD confinement. Taken together, these results demonstrate that the human genome is divided into large, discrete domains that are units of chromosome organization within the nucleus