Light- and electron-microscopic observations on the presence of pre-elastic (oxytalan) fibres around the mature cartilage in the external ear of the rat

Increased mesenchymal cell density accompanies induction of tropoelastin expression in developing elastic tissue

We studied the differentiation of elastin-producing fetal bovine chondrocytes to understand the regulatory processes associated with induction of elastin expression. Analysis of auricular elastic cartilage development in vivo indicated that differentiation of the prechondrogenic blastema to an elastogenic phenotype was preceded and accompanied by condensation of the mesenchymal cells. In addition, induction of elastin production was temporally and spatially linked to expression of type II collagen and proteoglycans. We assessed the influence of cell density on the induction of tropoelastin expression in pre-elastogenic cells from developing ear buds. Tropoelastin expression was induced in prechondrogenic mesenchymal cells only if the cells were maintained at a high cellular density. In addition, high density culture upregulated tropoelastin expression in fully differentiated chondrocytes. Together these data suggest that high cell density facilitates cell:cell interactions that affect cell proliferation and influence tropoelastin expression.

On the ultrastructure of the developing elastic cartilage in the rat external ear

Selected ultrastructural features of chondrocytes and the extracellular matrix in the developing elastic cartilage of the external ear were studied in rat fetuses and young animals. The cytoplasmic lipid droplets were first observed in the 19-day fetus. They increase in number and size during the first post-natal week. The elastogenesis proceeds in the sequence: oxytalan fibers (17-day fetus), elaunin fibers (1-day rat), elastic fibers (5-day rat). Intermediary stages between the randomly oriented individual microfibrils and bundles of microfibrils (oxytalan fibers) were also observed.

Ultrastructural distribution of sulfated complex carbohydrates in elastic cartilage of the young rabbit

Sulfated glycosaminoglycans are an integral component of elastic cartilage. We have investigated the ultrastructural distribution of sulfated complex carbohydrates (CC) in the mature cartilage and the perichondrium of young rabbit auricles using the high iron diamine-thiocarbohydrazide-silver proteinate (HID-TCH-SP) and the tannic acid-ferric chloride (TA-Fe) methods. In the mature cartilage, HID-TCH-SP stained intracellular Golgi saccules of the mature face, secretory granules, and the extracellular matrix granules, but staining was not discernible in collagen fibrils and osmiophilic elastic fibers consisting of only amorphous elastin. The HID and TA-Fe staining were similarly observed in matrix granules, whereas the elastic fibers and collagen fibrils lacked the staining. The pericellular matrix granules had a diameter of 34 +/- 5 nm (mean +/- SD; n = 30). Thiéry's periodate-TCH-SP (PA-TCH-SP) method stained vicinal glycol-containing CC in collagen fibrils but failed to stain matrix granules and elastic fibers. In the perichondrium, HID-TCH-SP staining of the organelles was less intense in the flattened chondrocytes when compared with those in large mature chondrocytes. The extracellular HID and HID-TCH-SP staining were observed in the matrix granules. The diameter of pericellular matrix granules (19 +/- 4 nm, mean +/- SD; n = 30) was significantly smaller when compared to those in the mature cartilage (P less than 0.001). The HID-TCH-SP staining was closely associated with collagen fibrils. However, the staining was not seen in collagen fibrils and osmiophilic elastic fibers consisting of elastin and microfibrils. The PA-TCH-SP method stained collagen fibrils and microfibrils but did not stain the amorphous elastin. Thus these studies demonstrate that sulfated CC are packaged in chondrocyte secretory granules and are released into the extracellular matrix to form matrix granules, but are not incorporated into collagen fibrils and elastic fibers.

Ultrastructure of mucocartilage in the larval anadromous sea lamprey, Petromyzon marinus L

The fine structure of mucocartilage, a tissue unique to larval lampreys, was examined in Petromyzon marinus L. This tissue is surrounded by a perichondrium of vascularized, dense connective tissue composed of fibroblasts, collagen fibrils, and elastic-like microfibrils, but it is avascular itself and consists of elastic-like microfibrils, ground substance, and a few diffusely scattered fibroblasts. Fibroblasts possess rough endoplasmic reticulum, may free ribosomes, a well-developed Golgi apparatus, a tubulo-vesicular network, and a number of secondary lysosomes containing crystalline material. The appearance of the organelles suggests the involvement of the cell in the synthesis and secretion of the ground substance and microfibrils. Tubular microfibrils, 11-13 nm in diameter, comprise the major portion of the matrix, and they are similar to those described in developing mammalian elastic tissue (Ross and Bornstein, 1969). The retention of the microfibrils may represent either a primitive form of elastic fiber in this "primitive" vertebrate or reflect the larval condition of the lampreys under examination. Scattered spherical to polyhedral-shaped mitrix granules and intergranular filaments make up the remainder of the matrix. It was concluded that mucocartilage in larval lampreys is not a conventional type of vertebrate connective tissue.

Tannic acid-glutaraldehyde fixative and pleomorphic adenomas of the salivary gland: an ultrastructural study

Four cases of pleomorphic adenomas of parotid glands were fixed by immersion in a mixture of 4% tannic acid and 3% glutaraldehyde followed by OsO4 postfixation and heavy metals staining. This clearly visualized the presence of dense amorphous elastic fibers in cellular and myxochondroid areas. The dense amorphous fibers were associated with varying numbers of peripheral filaments which appeared sometimes as bundles of parallel fibrils without intermingled amorphous material. These intermediate-sized filaments were seen indirect continuity with similar intracellular filaments with or without interposition of basal-membrane-like material and/or with extracellular filament-containing vesicles. It is suggested that these filaments are synthesized intracellularly and released into the extracellular space by neoplastic myoepithelial cells mainly by cytoplasmic vesicle separation. In addition, small round vesicles with a dense core of amorphous material and staining characteristics identical to those of extracellular elastin were frequently seen in the peripheral parts of these myoepithelial-like cells. It is possible that these dense-cored vesicles have a secretory function and contain a precursor of elastin.

Ultrastructure of elastic cartilage in the rat external ear

The structure of elastic cartilage in the external ear of the rat was investigated by transmission and scanning electron microscopy. The narrow subperichondrial, boundary zone contains predominantly ovoid cells rich in cell organelles: mitochondria, Golgi complex, granular endoplasmic reticulum and small (40--100 nm) vesicles. Scarce glycogen granules and bundles of 6--7 nm cytoplasmic filaments are also present. Deeper in the boundary zone, one or more cytoplasmic lipid droplets appear and cytofilaments become more abundant. Fully differentiated chondrocytes in the central zone of the cartilage plate resemble white adipose cells. They are globular and contain a single, large cytoplasmic lipid droplet. The cytoplasm is reduced to a thin peripheral rim; it contains a flattened nucleus, few cytoplasmic organelles and abundant, densely packed, cytoplasmic filaments. The intercellular matrix is very sparse. The pericellular ring consists of collagen fibrils about 20 nm in diameter and a proteoglycan cartilage matrix in the form of a "stellate reticulum". The complex of these two structures appears in the scanning electron micrographs as a a network of randomly oriented, ca 100 nm thick fibrils. Spaces between pericellular rings of matrix also contain thick elastic fibers or plates, apparently devoid of microfibrils. In scanning electron micrographs elastic fibers could be detected only in a few areas, in which they were not obscured by other constituents of the matrix. Immature forms of elastic fibers, oxytalan (pre-elastic) and elaunin fibers, were found in the perichondrial and boundary zones.