A unique cell type in the lung--the Clara cell (the non-ciliated bronchiolar epithelial cell).

The non-ciliated bronchiolar epithelial cells (the Clara cells) are found most frequently in the distal conducting airways, but they are found throughout the tracheobronchial tree of different mammalian species. According to recent data, the main functions of the Clara cells can summarized as (1), the secretion of certain components of the extracellular bronchiolar lining layer (2), metabolism and detoxification of xenobiotics and other toxic compound (3) and participation in the renewal process of the bronchiolar epithelium. The main goal of this paper is to collect and discuss some of the general features of Clara cells from a functional-morphological point of view, and their possible role in pathological alterations of the lung especially in the pathogenesis of lung tumours originated from Clara cells.

Nucleolar activity after 3-methylcholanthrene treatment of rat liver cells studied by silver staining procedure.

The influence of a single dose of 3-methylcholanthrene (3-MC) was studied in nucleoli of young rat liver cells by means of conventional and ultracytochemical methods. The nucleolar activity was stimulated in our experimental conditions: the appearance of the fibrillar centres in the liver cell nucleoli as well as the silver staining protein content of the fibrillar centres and the dense fibrillar component were increased by 3-MC. The results suggest that the activity of ribosomal genes was increased following 3-MC treatment.

Isolation and characterization of nuclear hnRNP complexes from Drosophila melanogaster tissue culture cells.

Fractionation on sucrose gradients of nuclear described extracts prepared from cultured Drosophila melanogaster cells by sonication of the nuclei in the presence of rat liver cytosol RNAase inhibitor revealed a complex polysome-like pattern of nuclear ribonucleoprotein complexes. The bulk of these heterogeneous ribonucleoprotein (hnRNP) complexes sedimented in the 30S to 80S zone of the sucrose gradient. According to biochemical and morphological data, the monomer particle proved to be the 45S hnRNP and its average diameter was found by electron microscopy to be 24-26 nm.

HnRNP particles from Drosophila melanogaster cells.

The isolation and characterization of HnRNP from cultured Drosophila melanogaster cells is described. HnRNP particles were extracted from the purified nuclei of sonication in the presence of rat liver cytosol RNAse inhibitor. The nuclear extract was centrifuged on a 15-30% sucrose gradient.

Structural characterization of polysomal poly(A)-protein particles in rat liver.

Poly(A)-protein particles were prepared from rat liver polyribosomes, washed with 0.5 M KCl or unwashed, after digestion with pancreatic ribonuclease and ribonuclease T1 by two successive rounds of sucrose gradient centrifugation. The particles were sedimented in a range of 5--13 S with a peak at about 9 S.

Studies on the structure of rat liver messenger ribonucleoprotein. II. Non-poly(A) RNase resistant fragments and electron microscopic appearance of mRNP.

Partially fragmented 12-21S rat liver messenger ribonucleoprotein (mRNP), labelled either with [3H]-orotic acid or [3H]-adenine was treated with 5 (micrograms/ml or 0.1 microgram/ml pancreatic ribonuclease (EC 3.1.

Swelling of nuclei and decondensation of chromatin in a multinuclear model.

Rat liver nuclei were isolated in the presence of a nonionic detergent, and the soluble proteins were extracted from them using low-salt solution. The isolated nuclei were then embedded in a fibrin clot which was cut into 4 to 5 mm3 pieces and placed into an AMICON pressure cell in the presence and absence of the soluble nuclear proteins. When the soluble nuclear proteins were present and when their concentrations reached 40 mg/ml, the nuclei were significantly larger and their chromatin more decondensed than in the absence of added proteins.

Effect of 3-methylcholanthrene on RNA polymerase and protein kinase activities and on the nuclear ultrastructure of rat liver.

The polycyclic aromatic hydrocarbon 3-methylcholanthrene (3-MC) is a well known inducer of the microsomal mixed function oxidase enzyme system in rat liver cells. It seems probable that the inductive action of 3-MC is realized, at least partly, at the transcriptional level of protein synthesis regulation. The present experiments indicated that in the liver of young rats there was a significant alteration in the activities of nucleolar as well as nucleoplasmic protein kinase and RNA polymerase enzymes during the first days of exposure to a single dose of 3-MC.

Perichromatin granules in the liver nuclei after isolation of hnRNP (informofer) particles.

The influence of the extraction of hnRNP (informofer) particles on the ultrastructural appearance of the perichromatin granules was studied. The extraction of hnRNP particles was carried out by SAMARINA's procedure from the rat liver nuclear fraction. The extraction did not change the numbers and the general ultrastructural features of perichromatin granules.

Electron microscopic observations on the poly(A)-RNP component of the pre-mRNA containing nuclear complexes.

The nuclear ribonucleoprotein particles containing polyadenylic acid were prepared from rat liver nuclear extract by treatment with RNase I. The sedimentation coefficient of the particles was approximately 14 S. These particles represent a component of the pre-mRNA containing ribonucleoprotein complexes of the nucleus.