Showing papers on "Cellular compartment published in 1975"

Electron microscopy of albumin synthesis

Abstract: Albumin molecules appeared to be synthesized in the light hepatocytes of rats by bound polysomers on rough and endoplasmic reticulum and the nuclear envelope. The molecules were discharged directly into the cytosol, then to the external cellular spaces. This conclusion failed to support the current theory from biochemical studies that albumin is synthesized by bound ribosomes, discharged into the cisternae of rough endoplasmic reticulum, and transported to the smooth endoplasmic reticulum and then to the Golgi apparatus. In addition to the liver, positive syntheic activities were observed in the aorta, kidney, and hepatoma cells of rat. Earlier investigators have reported that only liver cells can synthesize albumin.

The correlation of golgi activity and polysaccharide secretion in porphyridium12

Abstract: SUMMARY Quantitative morphometric measurements were made of the area occupied by the Golgi complex in log and stationary phase cells. The technique involved the cutting out and weighing of cellular compartments from electron micrographs of median cell sections. Data from the morphometric measurements combined with physiological measurements of secretory activity yielded a simple model for the involvement of the Golgi complex in the biogenesis of cell surface polysaccharides. Golgi were larger and more numerous in log phase, perhaps indicating a higher rate of polysaccharide synthesis than in stationary phase. In log phase, polysaccharide-containing vesicles accumulate adjacent to the cell membrane. In stationary phase, the polysaccharide is secreted to the cell surface by exocytosis, giving rise to a capsule. Thus the shift from log to stationary phase results in structural and functional cellular differentiation, eg, from a thin to a thick capsule. The ecological implications of capsule formation are discussed.

Golgi complex--endoplasmic reticulum transition region has rings of beads

Abstract: The smooth surface of the rough endoplasmic reticulum that makes the forming face of the Golgi complex has beadlike structures arranged in rings at the base of transition vesicles. The beads can only be seen easily after staining in bismuth salts. They are 10 to 12 nanometers in diameter and occur in a variety of cell types and organisms.

The synthesis and secretion of cartilage procollagen.

Abstract: 1. Isolation of free and membrane-bound ribosomes from embryonic chick sternal-cartilage cells labelled for 4min with [14C]proline and their subsequent analysis for hydroxy[14C]proline indicated that cartilage procollagen biosynthesis occurs on bound ribosomes. 2. Nascent procollagen polypeptides on bound ribosomes isolated from cells labelled with [14C]lysine were found to contain hydroxy[14C]lysine indicating that hydroxylation of lysine commences while the growing chains are still attached to the ribosomes. 3. Analysis of bound ribosomes labelled with either [14C]proline or [14C]lysine on sucrose density gradients indicated that cartilage procollagen is synthesized on large polyribosomes in the range 250-400S. 4. Microsomal preparations isolated from cells pulse-labelled for 4 min with [14C]proline were used to determine the direction of release of nascent procollagen polypeptides. Puromycin induced the vectorial release of nascent procollagen polypeptides into the microsomal vesicles suggesting that the first step in the secretion of procollagen polypeptides is their transfer from the ribosomes through the membrane of the endoplasmic reticulum into the cisternal space. 5. The procollagen polypeptides secreted by cartilage cells were shown to be linked by inter-chain disulphide bonds. 6. Examination of the state of aggregation of pro-alpha chains in subcellular fractions isolated from cartilage cells labelled with [14C]proline for various periods of time have provided data on the timing and location of inter-chain disulphide-bond formation. This process commences in the rough endoplasmic reticulum after the release of completed pro-alpha chains from membrane-bound ribosomes. Pro-alpha chains isolated from fractions of smooth endoplasmic reticulum were virtually all present as disulphide-bonded aggregates, suggesting that either disulphide bonding is completed in this cellular compartment, or that procollagen needs to be in a disulphide-bonded form to be transferred to this region of the endoplasmic reticulum. 7. Comparison of these results with previously published data on disulphide bonding in tendon cells suggest that the rate of inter-chain disulphide-bond formation is significantly slower in cartilage cells.

Ultrastructural analysis of the granulosa--luteal cell transition in the ovary of the dog.

Abstract: The transition from ovarian granulosa to lutein cell during the estrus cycle of 60 pregnant and non-pregnant beagle bitches was analyzed by light and electron microscopy (both 100 and 1000 KV). Early proestrus was characterized by a gradual rise in serum estrogen levels, hyperplasia of the granulosa cells, the accumulation of follicular fluid, and the development of tortuous intercellular channels. During the second half of proestrus, serum estrogen levels continued to rise, but growth, division, and differentiation of the granulosa cells was minimal. Estrus was marked by the first acceptance of the male and a well-defined LH peak In the subsequent 24 hour period, the granulosa-lutein cells hypertrophy rapidly and develop a large Golgi apparatus, small profiles of granular endoplasmic reticulum, numerous microfilaments, and large gap junctions between the cells. Mitochondria also proliferate, enlarge, and elongate, but retain lamelliform cristae. Luteinization of the cells and progesterone secretion begin just after ovulation which in turn occurs about 24 hours after the LH peak. On the third and fourth day of estrus, numerous small vesicles of agranular endoplasmic reticulum fill the cytoplasm and the mitochondria swell up and round off. The vesicles rapidly fuse into whorled and flattened cisternae or anastomosing tubules of agranular endoplasmic reticulum, while the mitochondria develop tubulovesicular cristae. These structures gradually become organized with respect to the basal lamina. The Golgi apparatus is centered over the pole of the nucleus that faces the pericapillary space. Stacked and whorled cisternae of agranular ER develop in the lateral margins and avascular end of the cell while mitochondria and tubular elements of agranular ER predominate in the central medial and most basal portions of the cytoplasm. Microfilaments are ubiquitous and appear to be instrumental in this orientation process. The cell surface develops three distinct regional specializations that coincide with the underlying cellular compartment: interconnecting pleomorphic folds fill the pericapillary space; long tenous microvilli project from the lateral cell surface and form tortuous intercellular channels and canaliculi; and large gap junctions form along the margins of the cell furthest removed from the basal lamina. By the sixth day of estrus, the granulosa-luteal cell transition is nearly complete and serum progesterone levels are on the rise.

Feinstrukturelle Untersuchungen an einem endokrin aktiven Carcinom der Nebennierenrinde

Abstract: The fine structure of a carcinoma of the human adrenal cortex clinically displaying Cushing’s disease was studied by electron microscopy. Besides irregular shapes and sizes of cells with deep invaginations and cytoplasmatic pseudoinclusions of their nuclei, the variability in distribution of cell organelles was remarkable. In comparison to animal experiments the organelles revealed evidence of increased endocrine activity demonstrated by an extensive development of rough and smooth endoplasmic reticulum, number of mitochondria, and Golgi apparatus; moreover lipid bodies were infrequent. By means of serial sectioning a direct connection between perinuclear space, rough and smooth reticulum, and interior of the Golgi apparatus could be traced. Most mitochondria exhibited a cristae type, several showed a gigantic size with a dense, finely granulated matrix. In addition there were septate interconnections between cellular membranes, membranes of the rough endoplasmic reticulum and cristae and mitochondrial membranes.