Structure of Collagen Fibrils as Revealed by Electron Microscopy

The elaboration of dentin collagen precursors by the odontoblasts in the incisor teeth of 30–40-g rats was investigated by electron microscopy, histochemistry, and radioautography after intravenous injection of tritium-labeled proline. At 2 min after injection, when the labeling of blood proline was high, radioactivity was restricted to the rough endoplasmic reticulum, indicating that it is the site of synthesis of the polypeptide precursors of collagen, the pro-alpha chains. At 10 min, when the labeling of blood proline had already declined, radioactivity was observed in spherical portions of Golgi saccules containing entangled threads, and, at 20 min, radioactivity appeared in cylindrical portions containing aggregates of parallel threads. The parallel threads measured 280–350 nm in length and stained with the low pH-phosphotungstic acid technique for carbohydrate and with the silver methenamine technique for aldehydes (as did extracellular collagen fibrils). The passage of label from spherical to cylindrical Golgi portions is associated with the reorganization of entangled into parallel threads, which is interpreted as the packing of procollagen molecules. Between 20 and 30 min, prosecretory and secretory granules respectively became labeled. These results indicate that the cylindrical portions of Golgi saccules transform into prosecretory and subsequently into secretory granules. Within these granules, the parallel threads, believed to be procollagen molecules, are transported to the odontoblast process. At 90 min and 4 h after injection, label was present in predentin, indicating that the labeled content of secretory granules had been released into predentin. This occurred by exocytosis as evidenced by the presence of secretory granules in fusion with the plasmalemma of the odontoblast process. It is proposed that pro-alpha chains give rise to procollagen molecules which assemble into parallel aggregates in the Golgi apparatus. Procollagen molecules are then transported within secretory granules to the odontoblast process and released by exocytosis. In predentin procollagen molecules would give rise to tropocollagen molecules, which would then polymerize into collagen fibrils.

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The morphogenesis of avian tendon

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1956.0011 ◽

1956 ◽

Vol 144 (917) ◽

pp. 556-572 ◽

Cited By ~ 67

Keyword(s):

Electron Microscopy ◽

Average Diameter ◽

Relative Volume ◽

Morphological Features ◽

Collagen Fibrils ◽

Intercellular Spaces ◽

Intercellular Substance ◽

Thin Sections ◽

Cellular Components ◽

Development Proceeds

Observations by electron microscopy on thin sections of the metatarsal tendon of embryonic fowls show that in the 8-day embryo the earliest definable collagen fibrils of 80 Å in diameter are intimately associated with the cytoplasm of the compact, apparently syncytial, cells of which the tendon rudiment is composed. As development proceeds, some intracytoplasmic groups of fibrils are distinguishable, but intercellular spaces also develop and these gradually become filled with fibrils; finally, bundles are formed and lie packed between the adjacent cells. Soon the extracellular organization predominates until at 20days the average diameter of the fibrils is 400 Å and the normal 640 Å periodicity of collagen has been achieved. The morphological features demonstrated have been correlated with histochemical data, and the possible function of the various cellular components in the formation of the intercellular substance has been discussed. By the use of sections in which fibrils have been cut exactly transverse to the bundle axis it has been shown that each fibril is invested by interfibrillar material. As the diameter of the fibrils increases with age the relative volume of interfibrillar material within a bundle diminishes; it is therefore concluded that this material must contain either collagen or the necessary precursors in order to account for the enlargement of the fibrils. Thus the interfibrillar material is of fundamental importance to the formation and growth of the collagen fibrils.

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Collagen Phagocytosis by Fibroblasts in the Periodontal Ligament of the Mouse Molar During the Initial Phase of Hypofunction

Journal of Dental Research ◽

10.1177/00220345870660120201 ◽

1987 ◽

Vol 66 (12) ◽

pp. 1708-1712 ◽

Cited By ~ 16

Author(s):

W. Beertsen

Keyword(s):

Electron Microscopy ◽

Morphometric Analysis ◽

Extracellular Space ◽

Periodontal Ligament ◽

Initial Phase ◽

Volume Density ◽

Collagen Fibrils ◽

Fibrillar Collagen ◽

Collagen Phagocytosis

This study was undertaken in order to determine whether hypofunction of teeth is associated with changes in collagen phagocytosis by fibroblasts of the periodontal ligament. In mice, the lower right molars were extracted and the animals killed one, two, three, four, or seven days later. The maxillary first molars with their surrounding periodontium were processed for electron microscopy and their periodontal ligament subjected to morphometric analysis. It was observed that, whereas the volume density of extracellular collagen in the ligament of the hypofunctional molars decreased from 50% to 30% during the course of the experiment the fraction of fibrillar collagen ingested by the cells increased over two-fold. This increase was already manifest very shortly after the onset of the experiment and offers an explanation for the net loss of collagen fibrils from the extracellular space.

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The precipitation of toroidal collagen fibrils

Biochemical Journal ◽

10.1042/bj1120515 ◽

1969 ◽

Vol 112 (4) ◽

pp. 515-519 ◽

Cited By ~ 11

Author(s):

Alan Cooper

Keyword(s):

Electron Microscopy ◽

Free Energy ◽

Lower Limit ◽

Small Proportion ◽

Helical Structure ◽

Collagen Fibrils ◽

Theoretical Considerations ◽

Continuous Injection ◽

Calf Skin

The morphology of aggregates of calf-skin tropocollagen, precipitated by continuous injection into neutral phosphate buffers at 35°, has been studied by electron microscopy. Although most of the collagen is precipitated as normal native fibrils, a small proportion forms closed toroidal structures having the usual native band–interband pattern. Theoretical considerations, based on elastic energies in a general microfibril model, predict that the toroids should have a simple super-helical structure, and this is not inconsistent with the observations. From the theoretical energies it was possible to estimate a crude lower limit of 3kcal./mole for the free energy of association of the tropocollagen macromolecules.

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Extracellular compartments in matrix morphogenesis: collagen fibril, bundle, and lamellar formation by corneal fibroblasts.

The Journal of Cell Biology ◽

10.1083/jcb.99.6.2024 ◽

1984 ◽

Vol 99 (6) ◽

pp. 2024-2033 ◽

Cited By ~ 176

Author(s):

D E Birk ◽

R L Trelstad

Keyword(s):

Electron Microscopy ◽

Cell Surface ◽

High Voltage ◽

Collagen Fibril ◽

Corneal Stroma ◽

Collagen Fibrils ◽

High Voltage Electron Microscopy ◽

Voltage Electron ◽

High Voltage Electron ◽

Corneal Fibroblasts

The regulation of collagen fibril, bundle, and lamella formation by the corneal fibroblasts, as well as the organization of these elements into an orthogonal stroma, was studied by transmission electron microscopy and high voltage electron microscopy. Transmission and high voltage electron microscopy of chick embryo corneas each demonstrated a series of unique extracellular compartments. Collagen fibrillogenesis occurred within small surface recesses. These small recesses usually contained between 5 and 12 collagen fibrils with typically mature diameters and constant intrafibrillar spacing. The lateral fusion of the recesses resulted in larger recesses and consequent formation of prominent cell surface foldings. Within these surface foldings, bundles that contained 50-100 collagen fibrils were formed. The surface foldings continued to fuse and the cell surface retracted, forming large surface-associated compartments in which bundles coalesced to form lamellae. High voltage electron microscopy of 0.5 micron sections cut parallel to the corneal surface revealed that the corneal fibroblasts and their processes had two major axes at approximately right angles to one another. The surface compartments involved in the production of the corneal stroma were aligned along the fibroblast axes and the orthogonality of the cell was in register with that of the extracellular matrix. In this manner, corneal fibroblasts formed collagen fibrils, bundles, and lamellae within a controlled environment and thereby determined the architecture of the corneal stroma by the configuration of the cell and its associated compartments.

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Electron Microscopy of Collagen Fibrils During Cortisone Therapy of Alopecia Totalis (Technical Problems)1

Journal of Investigative Dermatology ◽

10.1038/jid.1955.116 ◽

1955 ◽

Vol 25 (3) ◽

pp. 175-178 ◽

Cited By ~ 3

Author(s):

Reginald A. Wilson ◽

Julius L. Danto ◽

Stuart Maddin

Keyword(s):

Electron Microscopy ◽

Collagen Fibrils ◽

Technical Problems ◽

Cortisone Therapy

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Electron Microscopy of Wound Healing in Patients with Hernia

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100115389 ◽

1975 ◽

Vol 33 ◽

pp. 352-353

Author(s):

C.N. Sun ◽

H.J. White ◽

R.C. Read

Keyword(s):

Electron Microscopy ◽

Wound Healing ◽

Phosphate Buffer ◽

Osmium Tetroxide ◽

Phosphotungstic Acid ◽

Rectus Sheath ◽

Uranyl Acetate ◽

Collagen Fibrils ◽

Lead Citrate ◽

Native Collagen

Previously we have reported the defect of collagen fibrils from herniated rectus sheath. This presentation includes additional sections from postsurgical incisions (10 days) from both control and hernia patients. Small pieces of rectus sheath were fixed in 3% glutaraldehyde in phosphate buffer (pH 7.2) and post fixed with buffered 2% osmium tetroxide. The tissues were then dehydrated in serially increasing concentrations of alcohol and embedded in Epon 812. Sections were stained with 2.5% phosphotungstic acid or uranyl acetate and lead citrate.Previously we found that collagen fibrils from "non-herniated" rectus sheath have uniform diameters and 640 Å periodicity with seven or more intraperiodic bands resembling typical native collagen fibrils, while the fibrils from fascia obtained from patients with direct herniation show considerable variation in diameter. These variations are often found in the same individual fibers with a range from 300 Å to 3000 Å.

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Supramolecular structure of polymorphic collagen fibrils.

The Journal of Cell Biology ◽

10.1083/jcb.68.3.521 ◽

1976 ◽

Vol 68 (3) ◽

pp. 521-538 ◽

Cited By ~ 34

Author(s):

R R Bruns

Keyword(s):

Electron Microscopy ◽

Banding Pattern ◽

Collagen Fibrils ◽

Graphic Method ◽

Interaction Sites ◽

Symmetrical Pattern ◽

Native Collagen ◽

Major Period ◽

Polymorphic Forms ◽

Specific Band

Reconstituted cartilage collagen fibrils with an oblique banding pattern or with two types of symmetrical patterns, and reconstituted rattail tendon fibrils with a third type of symmetrical pattern were examined by electron microscopy and found to consist of narrow subfibrils having native-type cross-striations. Analysis of the four types of patterns by a graphic method of specific band matching revealed the orientation and axial relation of individual subfibrils and their component molecules. In fibrils with an oblique pattern, subfibrils have the same orientation and a regular 100A axial displacement. Observations on staining characteristics, folded fibrils, and transverse sections of embedded fibrils suggest that the obliquely banded fibrils are ribbonlike or layered structures. In the three types of fibrils with a symmetrical pattern, adjacent subfibrils are oppositely oriented and aligned within a 119-A segment of the 670-A major period. Considered together, the observations suggest that interaction sites on the surface of subfibrils (and perhaps on the surface of native collagen fibrils) occur in various patterns that are manifested accouding to the nature of the environment during fibril formation, and that such patterns can be mapped on the surface of subfibrils by noting the arrangement of subfibrils in polymorphic forms.

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The ultrastructural organization of proteoglycans and collagen in human and rabbit scleral matrix

Journal of Cell Science ◽

10.1242/jcs.74.1.95 ◽

1985 ◽

Vol 74 (1) ◽

pp. 95-104

Author(s):

R.D. Young

Keyword(s):

Electron Microscopy ◽

Articular Cartilage ◽

Collagen Fibrils ◽

Ultrastructural Organization ◽

Connective Tissues ◽

Collagen Organization ◽

Band Position ◽

Cuprolinic Blue ◽

Relationship Of ◽

Fibril Diameter

The distribution of proteoglycans and their association with collagen fibrils were studied in human and rabbit sclera following fixation of tissue in glutaraldehyde containing Cuprolinic Blue, a specific stain for proteoglycans when used in the presence of critical concentrations of electrolytes. Proteoglycans were visualized by electron microscopy as fine filaments, approximately 54 nm in length and 5 nm in diameter, associated with the d band in the gap zone of the periodic collagen banding pattern. Filaments were present in three orientations: (1) radiating from the d band to associate with corresponding sites on adjacent collagen fibrils; (2) encircling the collagen fibril at the d band position; and (3) lying along the fibril axis, often linking consecutive d bands. No difference was apparent between the proteoglycan-collagen organization in human and rabbit sclera. A similar arrangement of proteoglycan filaments in association with the d band was also evident throughout all levels of the sclera in spite of considerable variations in fibril diameter from inner to outer stroma. Furthermore, the specific relationship of proteoglycans with the collagen fibrils in sclera closely resembled that previously described in tendon and in articular cartilage, lending support to the view that the association of proteoglycans with collagen may be consistent in a majority of connective tissues, irrespective of their diverse functional specializations.

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