Thymic nurse cells: morphological study during their isolation from murine thymus

Summary Thymic nurse cells (TNC), which are multicellular complexes composed of epithelial cells and thymocytes, were obtained from C3H-mice thymuses. They were described by means of light and electron microscopy. The morphology of epithelial cells forming isolated TNC compared to that of small tissue fragments obtained by enzymatic digestion revealed that TNC could be derived from all parts of the thymus: cortex, corticomedullary junction and medulla, the cortex being their principal source. This variety of origin, the presence of several epithelial cells inside a single TNC, the presence of non-lymphoid cells, and the various locations of eleaved desmosomes confirmed that their aspect in vitro as round and sealed structures can be considered to be an artifact due to the isolation technique used. Indeed, during this procedure, they are formed by a process of wrapping of the epithelial cytoplasm around the tightly associated thymocytes. All three epithelial cell types: cortical reticular cells, medullary reticular cells, and medullary globular cells can form TNC.A portion of this work was presented at the first Thymus Workshop. Rolduc, Netherlands, April, 1988     

Molecular cloning and expression of a proteinase gene from Lactococcus lactis subsp. cremoris H2 and construction of a new lactococcal vector pFX1

The 6.5 kb HindIII DNA fragment of the Lactococcus lactis subsp. cremoris H2 plasmid pDI21 was cloned into Escherichia coli POP13 with NM1149, and also directly into Lactococcus lactis subsp. lactis 4125 using a newly-constructed broad host-range vector pFX1. Proteinase was experessed in both transformed organisms. The proteinase resembles a PI type since it preferentially degraded -casein. The restriction map of the 6.5 kb proteinase gene fragment has minor differences from those of published plamid proteinase genes. High-efficiency electroporation with pFX1 provides a direct approach for gene cloning in lactococci.Abbreviations cfu colony forming units - HEPES N-[2-hydroxyethyl]piperazine-N-[2-ethanesulphonic acid] Dedicated to Prof. Dr. G. Drews on the occasion of his 65th birthday     

Regulation of pyrimidine biosynthesis in Pseudomonas cepacia

Pyrimidine biosynthesis was investigated in Pseudomonas cepacia ATCC 17759. The presence of the de novo pyrimidine biosynthetic pathway enzyme activities was confirmed in this strain. Following transposon mutagenesis of the wild-type cells, a mutant strain deficient for orotidine 5-monophosphate decarboxylase activity (pyrF) was isolated. Uracil, cytosine or uridine supported the growth of this mutant. Uracil addition to minimal medium cultures of the wild-type strain diminished the levels of the de novo pyrimidine biosynthetic enzyme activities, while pyrimidine limitation of the mutant cells increased those de novo enzyme activities measured. It was concluded that regulation of pyrimidine biosynthesis at the lelel of enzyme synthesis in P. cepacia was present. Aspartate transcarbamoylase activity was found to be regulated in the wild-type cells. Its activity was shown to be controlled in vitro by inorganic pyrophosphate, adenosine 5-triphosphate and uridine 5-phosphate.     

Underwater observations of piranhas in western Brazil

Synopsis The behaviour of three piranha species,Serrasalmus marginatus, S. spilopleura, andPygocentrus nattereri, and their prey fishes was studied underwater in the Pantanal region, Mato Grosso, Brazil. General habits, predatory tactics, feeding behaviour, and social interactions while foraging, as well as defensive tactics of prey fishes were observed.S. marginatus is solitary whereas the other two species live in shoals; their agonistic behaviour varies accordingly, the simplest being displayed by the solitary species. Predatory tactics and feeding behaviour also vary:S. spilopleura shows the most varied diet and highly opportunistic feeding strategy, which includes aggressive mimicry. The solitaryS. marginatus, besides fin and scale-eating, occasionally cleans larger individuals ofP. nattereri. Several cichlid species display defensive tactics clearly related to piranha attacks: tail protecting, watching, and confronting the predator are the most commonly observed behaviours. Piranhas seem to strongly influence use of habitat, social structure, and foraging mode of the fish communities.     

大鼠隔—海马通路损伤对海马内递质含量及酶活力的影响

单侧切断大鼠海马缴和部分穹窿可使海马部分去神经。损伤后7d,海马内胆碱能系统中乙酰胆碱(ACh)含量下降72.5%,胆碱乙酰基转移酶(ChAT)活力下降45.7%,胆碱酯酶活力下降52.2%,在单胺能系统中,去甲肾上腺素(NA)含量下降16.3%,多巴胺(DA)含量下降31.3%,5-羟色胺含量下降30.3%。在损伤过程中,海马内氨基酸含量没有改变。实验结果表明,海马缴和穹窿是脑内胆碱能和单胺能传入神经到达海马靶区的部分共同通路。     

Histopathology and cell culture characteristics of liver cells from grc − and grc + rats given diethylnitrosamine

The histopathological response and cell culture characteristics of liver cells from the R16 (grc ^–) strain of rats, which carries an MHC-linked deletion, were examined one week after a single intraperitoneal injection of 200 mg/ kg body weight diethylnitrosamine (DEN) and were compared with the response of liver cells from wild type (grc+) rats. The DEN exposure induced hydropicl vacuolar changes in the parenchymal cells and a limited proliferation of oval cells in the periportal areas of the livers of both grc+ and grc rats. Primary culture of collagenase-digested livers consisted of parenchymal, bile ductular and oval-related cells as determined by cell-specific immunohistochemistry. Subpassaged cells from grc+ rats exhibited oval cell ultrastructural morphology, inducible histochemical staining for gammaglutamyl transpeptidase (GGT), and DEN-associated onset of anchorage-independent growth. Primary cultures of liver cells from R16 rats consistently failed to form cell strains upon subpassage.Abbreviations DEN diethylnitrosamine - grc growth and reproduction complex - GGT gamma-glutamyl transpeptidase - MHC major histocompatibility complex     

Multiple episodes of induced secretion of human growth hormone from recombinant AtT-20 cells

Recombinant AtT-20 cells expressing human growth hormone (hGH) secreted the hormone at a constant, basal rate of 0.3–0.5 ng/10⁵ cells-hour when exposed to medium without secretagogues. When triggered with 8 bromo-cyclic AMP, cells secreted hGH at an initial rate of 1.7 ng/10⁵ cells-hour while intracellular hGH declined sharply. Upon extended exposure to secretagogue, secretion decreased gradually to the basal rate and intracellular hGH stabilized at a value 40% the initial. In cells switched from secretion to growth medium, the total rate of hGH accumulation intracellularly and in medium was 2.2 times that observed with cells never exposed to secretagogue; however, only a fraction of the hormone was stored intracellularly and the rest was secreted. When cells were exposed alternately to growth and secretion medium, induced cells secreted at rates at least two times higher than uninduced controls during the first five cycles. The induced response deteriorated with time, however, in parallel with outgrowth of attached cells by foci of round cells, and by the eighth cycle induced secretion did not occur. Operational modifications that may improve the performance of cycling schemes are discussed.     

Initial steps in the degradation of benzene sulfonic acid, 4-toluene sulfonic acids,and orthanilic acid in Alcaligenes sp. strain O-1

Alcaligenes sp. strain O-1 grew with benzene sulfonate (BS) as sole carbon source for growth with either NH₄ ⁺ or NH₄ ⁺ plus orthanilate (2-aminobenzene sulfonate, OS) as the source(s) of nitrogen. The intracellular desulfonative enzyme did not degrade 3- or 4-aminobenzene sulfonates in the medium, although the enzyme in cell extracts degraded these compounds. We deduce the presence of a selective permeability barrier to sulfonates and conclude that the first step in sulfonate metabolism is transport into the cell. Cell-free desulfonation of BS in standard reaction mixtures required 2 mol of O₂ per mol. One mol of O₂ was required for a catechol 2,3-dioxygenase. When meta ring cleavage was inhibited with 3-chlorocatechol in desalted extracts, about 1 mol each of O₂ and of NAD(P)H per mol of BS were required for the reaction, and SO₃ ^2- and catechol were recovered in high yield. Catechol was shown to be formed by dioxygenation in an experiment involving ¹⁸O₂. 4-Toluene sulfonate was subject to NAD(P)H-dependent dioxygenation to yield SO₃ ^2- and 4-methylcatechol, which was subject to meta cleavage. OS also required 2 mol of O₂ per mol and NAD(P)H for degradation, and SO₃ ^2- and NH₄ ⁺ were recovered quantitatively. Inhibition of ring cleavage with 3-chrorocatechol reduced the oxygen requirement to 1 mol per mol of OS SO₃ ^2- (1 mol) and an unidentified organic intermediate, but no NH₄ ⁺, were observed.