We have investigated the early cellular events that take place during the change in lineage commitment from hypertrophic chondrocytes to osteoblast-like cells. We have induced this osteogenic ...differentiation by cutting through the hypertrophic cartilage of embryonic chick femurs and culturing the explants. Immunocytochemical characterization, 3 Hthymidine pulse-chase labeling, in situ nick translation or end labeling of DNA breaks were combined with ultrastructural studies to characterize the changing pattern of differentiation. The first responses to the cutting, seen after 2 d, were upregulation of alkaline phosphatase activity, synthesis of type I collagen and single-stranded DNA breaks, probably indicating a metastable state. Associated with the change from chondrogenic to osteogenic commitment was an asymmetric cell division with diverging fates of the two daughter cells, where one daughter cell remained viable and the other one died. The available evidence suggests that the viable daughter cell then divided and generated osteogenic cells, while the other daughter cell died by apoptosis. The results suggest a new concept of how changes in lineage commitment of differentiated cells may occur. The concepts also reconcile previously opposing views of the fate of the hypertrophic chondrocyte.
Background: Expression of aggrecan is reduced during aging and osteoarthritic cartilage degeneration. CpG methylation may have a role in the down regulation of aggrecan transcriptions. Objective: To ...investigate whether a correlation between gene methylation and expression of aggrecan in chondrocytes exists. Methods: The human aggrecan promoter region was analysed computationally for CpG-rich regions. These were investigated for the methylation of C residues in normal (aged) and osteoarthritic chondrocytes by the bisulphite method for modifying DNA as well as sequence analysis using DNA directly extracted from normal and osteoarthritic cartilage tissue. Additionally, chondrocytic cell lines were investigated for methylation within the aggrecan promoter region. Results: The CpG-rich promoter region of the human aggrecan gene contains a 0.6 kb region that meets the criteria of a CpG island as defined by prediction programmes. A significant correlation of aggrecan mRNA expression levels and methylation status in normal (aged) and osteoarthritic chondrocytes as well as in different chondrocytic cell lines was not found. Conclusions: Expression of aggrecan in normal cartilage and diseased states is not modulated by gross changes of CpG methylation of its promoter region. CpG methylation does not have a central role in the switch off of aggrecan promoter activity in human adult articular chondrocytes.
Sequence stratigraphy in deeper water, epicontinental carbonates such as in the Upper Jurassic of southern Germany is difficult because the recognition of parasequences, sequences and sequence ...boundaries is impeded by the paucity in diagnostic sedimentological criteria or stratal surfaces. Using the “genetic stratigraphic” approach, and integrating facies, stable isotope (C, O) and palynofacies analysis two types of genetic depositional sequences can be discriminated: small-scale sequences are stacked into medium-scale sequences which may record a 400 kyr Milankovitch signal. The medium-scale sequences were correlated regionally using both gamma-ray logs and stable isotope records. Regional correlations show that the depocentres are controlled by underlying palaeotectonic elements (Late Palaeozoic troughs).
The rise/fall turnarounds of medium-scale sequences are marked by negative δ
18O peaks (temperature maxima) and reduced absolute palynoclast contents.
The fall/rise turnarounds are marked by positive δ
18O peaks (temperature minima) and high absolute palynoclast contents. The initiation and termination of sponge/microbial mounds show characteristic patterns: thrombolitic microbialites form during intervals of (1) reduced input of terrestrial palynomorphs interpreted as an increase in distality, (2) decreasing δ
13C trends interpreted to be related to decreasing nutrient supply and (3) decreasing δ
18O values interpreted as phases of warming and rising relative sea-level. In contrast, thrombolitic/stromatolitic microbialites were found to occur during phases of (1) increasing input of terrestrial palynomorphs interpreted as an increase in proximality, (2) increasing δ
13C values interpreted to reflect increasing terrestrial input and nutrient supply as well as increasing δ
18O values (interpreted as phases of cooling and relative sea-level falls). Isotopic and palynofacies evidence suggests that bioherms were terminated by sudden input of nutrients during relative sea-level falls.
Sedimentological criteria were clearly not sufficient to delineate a robust sequence stratigraphic framework.
The Middle Permian to Lower Triassic Khuff Formation is one of the world's most prolific hydrocarbon reservoirs. This study is part of a research project on Khuff outcrop equivalents whose overall ...aim is to investigate the reservoir architecture on different scales. The present paper focuses on heterogeneities in Khuff‐equivalent grainstones at the near well scale.
An outcrop in the Oman Mountains, where the Khuff‐equivalent Saiq and Mahil Formations are exposed in an area 1800 m long by 100 m high, was studied to map lateral and vertical depositional heterogeneities. The investigated section represents parts of three third‐order sequences: the upper part of Khuff sequence (KS)3 (grain‐dominated), the whole of KS2 (mud‐dominated), and the lower part of KS1 (grain‐dominated). Real‐Time Kinematic GPS, satellite imagery, outcrop gamma‐ray and digitized sedimentary logs were used for outcrop description and were integrated into a three‐dimensional digital outcrop model.
The resulting 3D facies model indicates that the apparently simple, layer‐cake geometry of the grainstone reservoir facies shows pinching and swelling with a standard deviation of 12.75% of bed thickness. These thickness variations may influence volume calculations during reservoir assessments. The heterogeneities of grainstone bodies are represented by compositional (ooid, peloid or intraclast‐dominated) and grain‐size variations.
Muddy event beds at the cm‐scale were mapped out in detail in a 200 × 40 m outcrop window and together form a dense network of potential baffles to fluid flow. The thickness of these beds varies significantly due to syndepositional erosion.
An important conclusion of this near well‐scale study is that the perceived simple, layer‐cake Khuff‐equivalent succession in the study area is in fact heterogeneous in mud‐rich deposits, while grain‐rich deposits extend over a wide area with some thickness variations. These findings can be directly applied in Khuff subsurface correlation and modelling attempts.
BACKGROUND & AIMS: Collagenous colitis is a rare diarrheal disease of unknown pathophysiology that is histologically defined by subepithelial bandlike structures. The objective of this study was to ...elucidate the biochemical composition and the origin of the bandlike structures in collagenous colitis.
METHODS: Immunohistochemical and in situ hybridization analyses were performed on endoscopic specimens using specific antibodies and riboprobes for collagen types I, III, IV, and VI and for the glycoprotein tenascin.
RESULTS: In collagenous colitis, the mucosal matrix with the exception of the bands retained a normal architecture and extracellular matrix composition. The bands stained most prominently for type VI collagen and tenascin. Less abundant staining for both proteins was also found in the subepithelial matrix of the normal mucosa. In situ hybridization showed no significant increase in collagen type VI messenger RNA expression in cells around and entrapped in the bands in collagenous colitis compared with normal specimens.
CONCLUSIONS: The results support the suggestion that collagenous colitis is a localized alteration of the extracellular matrix, which involves the pericryptal-subepithelial myofibroblast sheath. The data suggest that reduced matrix degradation and not overactivation of matrix synthesis may be the reason for the subepithelial accumulation of matrix proteins. (Gastroenterology 1997 Jul;113(1):136-43)
Durable healing of full-thickness articular cartilage defects has been considered for a long time as a highly desirable, but unlikely event to occur. In recent years, conflicting reports on the ...outcome of in vitro and in vivo studies on chondrocyte and cartilage grafting into animal and human joints have raised new arguments for and against controlled repair of articular cartilage following injury. Some of the problems result from insufficient characterization of implant and repair tissue, and from too short follow up phases. Here we describe a new approach to repair articular cartilage defects in rabbit knees by allografting chondrocytes cultured in agarose gels.
The implants were monitored over 6-18 months and graded histologically, immunohistochemically, and electron microscopically, using a grading scale based on seven evaluation criteria. Control implants of pure agarose produced poor fibrous substitute tissue, insufficient healing and incomplete filling of the cartilage defects. After transplantation of allogenic chondrocytes embedded in agarose, the quality of the newly formed repair cartilage was superior with respect to type II collagen and proteoglycan content and cellular architecture when compared with untreated defects. Superficial fibrillation and degradation were significantly diminished or prevented.
New subchondral bone formed at the level of the previous subchondral bone. In most cases the repair tissue merged with the host articular cartilage; normal calcified cartilage was the only tissue zone that did not participate in the integration of the transplant. By gross evaluation 24% of grafts showed an extent of recovery never observed in controls. The best results were obtained after 18 months when 47% of the grafts (N = 15) developed a morphologically stable hyaline cartilage.
These studies demonstrate that agarose-embedded chondrocyte may prove a valuable tool for controlled repair of articular cartilage defects.
The Lower Triassic Rogenstein Member of the Buntsandstein Formation produces gas at the De Wijk and Wanneperveen fields, NE Netherlands and consists mainly of claystones with intercalated oolitic ...limestone beds. The excellent reservoir properties of the oolites (φ= 20‐30%; k = 5‐4000 mD) are predominantly controlled by depositional facies. Oolitic limestones are interpreted as the storm and wave deposits of a shallow, desert lake located in the Central European Buntsandstein Basin.
The vertical sequence of lithofacies in the Rogenstein Member indicates cyclic changes of relative lake level. The reservoir rock is vertically arranged in a three‐fold hierarchy of cycles, recognised both in cores and wireline logs. These cycles are a key to understanding the distribution of reservoir facies, and are used as the basis for a high‐resolution sequence stratigraphic correlation of the reservoir units.
Slight regional‐scale thickness variations of the Rogenstein Member (in the order of tens of metres) are interpreted as the effects of differential subsidence associated with the inherited Palaeozoic structural framework. The depositional basin can be subdivided into subtle palaeo‐highs and ‐lows which controlled facies distribution during Rogenstein deposition. Oolitic limestones show their greatest lateral extent and thickest development in the Middle Rogenstein during large‐scale maximum flooding.
Potential reservoir rocks (decimetre to metres thick) are present in the NE Netherlands, in particular in the Lauwerszee Trough and the Lower Saxony Basin, where abundant gas shows of 200 ‐ 4000 ppm CH4 have been recorded. Preserved primary porosity is interpreted to be a result of rapid burial in subtle depositional palaeo‐lows in this area. The thickest, amalgamated oolite intervals (tens of metres thick) occur in the eastern part of the Central Netherlands Basin. Because of poor reservoir properties, other areas appear to be less promising in terms of Rogenstein exploration potential.
Cushing's syndrome can be caused by adrenocorticotropic hormone-secreting solid tumors. We report a rare case of an ileal endocrine carcinoma that produced ACTH and induced hypercortisolism. A now ...47-year-old man presented at age 41 with weight gain, tremor, perspiration, and general fatigue. Laboratory testing showed hypercortisolism and diabetes mellitus. Further examinations revealed ectopic Cushing's syndrome. The search for the primary tumor was difficult. The patient underwent subtotal thyroidectomy and surgical removal of a pituitary lesion. After resection of an ACTH-producing metastasis of the mesentery, temporary remission of Cushing's syndrome ensued. At the age 45 the primary tumor was detected in the ileum by Ga-68 DOTATOC-PET scan and explorative laparotomy. After surgical removal of this well differentiated neuroendocrine carcinoma the patient significantly improved clinically. He experienced better blood pressure and remission of his diabetes mellitus in addition to increased muscular strength. Endocrine laboratory testing at follow-up examinations confirmed remission of hypercortisolism and diabetes mellitus. A Ga-68 DOTATOC PET scan and a 1 mg dexamethasone suppression test 5 months after surgery showed normal results. Ectopic ACTH secretion within the small bowel is very rare. This case underscores the difficulty in locating the source of ectopic ACTH secretion and suggests using small bowel barium study, tubus endoscopy or video endoscopy for preoperative localization if the small bowel is suspected as tumor source.
...chondrocytes of osteoarthritic cartilage are generally thought to be anabolically hyperactive. ...in osteoarthritic cartilage degeneration, the ongoing net loss of the cartilage matrix components ...is attributed not to a lack of synthesis of cartilage matrix molecules by the cartilage cells, but to an increase in matrix catabolism by most authors. 1-3 In contrast, our in situ analysis on the single cell level showed a suppression of aggrecan and collagen type II expression in the chondrocytes in the upper cartilage zone, which is critical for the progression of the cartilage destruction.
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