Are Chaoborus larvae more abundant in acidified than in non-acidified lakes in Central Canada?

Eriksson et al (1980) hypothesized that the abundance of certain macroinvertebrate predators, such as larvae of the phantom midge Chaoborus , should increase in acidified lakes because of the elimination of fish. To examine the influence of pH and presence of fish on Chaoborus abundance, we surveyed Chaoborus populations in 33 lakes in Ontario, Canada which ranged in pH from 4.5 to 7.4. Chaoborus larvae were not more abundant in the acidified lakes that were devoid of fish than in the remaining lakes. Therefore, we concluded that pH and presence of fish are not prime determinants of total Chaoborus abundance in Canadian Shield lakes. We hypothesized that significant increases in Chaoborus abundance should only be anticipated when fish populations are eliminated by acidification of relatively nutrient rich lakes.     

Influence of both coculture and BrdU on NOR activity of mouse,rat and human cells

Summary The coculture of mouse PG19 cells with human MGC cells can significantly suppress nucleolar organizer region (NORs) activity of both PG19 and MGC cells. 5-bormodeoxyuridine (BrdU) can also significantly suppress the NOR activity of rat RC cells, human MGC and Hela cells, and mouse PG19 cells: i.e. the average number of Ag-NORs and the number of chromosomes bearing Ag-NORs per cell decrease significantly. The degree of the suppression increases with increase in both BrdU concentration in the culture medium and BrdU treatment time. The suppressed NOR activity of the PG19 cells can gradually be restored when the BrdU-treated cells are transferred into BrdU-free medium for 50 h. In PG19 cells deoxycytidine (dC) can reverse the suppression of NOR activity caused by BrdU. Coculture plus BrdU treatment suppress the NOR activity of PG19 cells more severely than BrdU treatment alone. In coculture medium containing 30 g BrdU/ml, dC can also reverse the suppression of the NOR activity of PG19 cells but not that of the MGC cells. The degree of the reversion in the coculture plus BrdU treatment is significantly lower than that found with BrdU-treatment alone.     

Post-translational modifications of proteins: some problems left to solve

Three major questions regarding the post-translational modification of amino acid side chains in proteins are briefly considered: (1) What are the biological functions of the reactions, (2) what is the specificity of the processing reactions in selecting only a few or sometimes even only one residue for modification, and (3) how do we solve the uniqueness of the processing steps in the production of recombinant proteins? The answers to these questions are not obvious at this time.     

Activation of murine T cells by toxic shock syndrome toxin-1. The toxin-binding structures expressed on murine accessory cells are MHC class II molecules

Toxic shock syndrome toxin-1 (TSST-1)-binding structures present on murine lymphoid tissues were investigated by using 125I-TSST-1. T-depleted C57BL/6 spleen cells incubated with TSST-1 for 3 h at 0 degree C were mitogenic to splenic T cells, indicating that the former cells bind and present TSST-1 to T cells. TSST-1-binding activity was observed in C57BL/6 splenic B cells and L cells transfected with I-Ab genes, but not in splenic T cells and control L cells. Scatchard plot analysis showed that these B cells and transfectants bound TSST-1 with similar binding affinity. SDS-PAGE analysis showed that lysates of C57BL/6 spleen cells and the I-Ab-positive transfectants contain a single band which bound TSST-1 and comigrated with I-Ab heterodimers. TSST-1-binding activity observed clearly in C57BL/6. BALB/c, and C3H/HeN spleen cells and L cells transfected with I-Ab or I-Ak genes was not reduced by paraformaldehyde fixation. Binding of 125I-TSST-1 to the three spleen cells was markedly reduced by anti-I-A antibodies, but not by anti-I-E antibodies. C57BL/6, C3H/HeN, and (C3H/HeN x C57BL/6) F1 T cells were activated by TSST-1 to proliferate and produce IL-2 in the presence of FT6.2 cells, LT1-30-3 cells and either of them, respectively, but not in the presence of control L cells. These results indicate that I-A molecules function as the structures via that accessory cells directly bind TSST-1 on the cell surface and present a triggering signal of TSST-1 to T cells.     

Amplification of multicistronic plasmids in the human 293 cell line and secretion of correctly processed recombinant human protein C

We have constructed multicistronic vectors containing the cDNAs for murine dihydrofolate reductase (DHFR), hygromycin phosphotransferase (HyPR), and human protein C (HPC), an antithrombotic factor. Using a sequential selection protocol with hygromycin (Hy) and methotrexate (MTX), we demonstrate the selective amplification of the murine dhfr cDNA in the adenovirus-transformed human kidney cell line 293, and the coamplification of the cDNA for HPC. Such recombinant 293 cell lines secreted HPC at levels as high as 25 micrograms/10(6) cells/day. In addition, we found that the complex vitamin K-dependent posttranslational modification of gamma-carboxylation of glutamate was not limiting at these high secretion levels, although the proteolytic processing of the protein was slightly reduced. Further, the HPC secreted from the gene-amplified cell lines had full anticoagulant activity when compared to plasma-derived HPC.     

心肌细胞间的电耦联

心脏是由无数个独立的心肌细胞通过缝隙连接形成的一个功能性合胞体。心肌细胞间的电耦联是心脏“全或无”性动作电位传导和机械收缩的先决条件。缺氧、缺血、药物、细胞内外离子浓度的改变以及激素等因素可直接或间接地影响心肌细胞间的电耦联,从而导致心脏功能的改变。     

向日葵离体孤雌生殖的超微结构研究

本文是研究未受精胚珠培养诱导的孤雌生殖过程超微结构变化的首次报道。向日葵(Heliaanthus annuus L.)的卵细胞在离体条件下被激活,发生细胞核移位、极性丧失、细胞器增多并转变成活动状态、液泡化程度增大、合点端形成细胞壁等一系列变化,预示即将启动孤雌生殖。孤雌生殖的原胚具有若干显著特征,如极性颠倒、有自体吞噬活动、壁的自由生长、游离核分裂等。对这些现象作了初步的讨论。     

湖北菱科植物的数量分类研究 Ⅲ.分类性状的定量评价

用R聚类分析和主分量分析,定量研究了湖北菱科5种8变种37个形态和生态性状的变异及分类学价值。结果表明,植物体大小变异是形态演化的主要方向之一。形态演化的同时,也发生生态分化。除少数性状例外,形态演化与生态分化在相当程度上是独立的。     

A SPOROPHYTE CELL WALL PROTEIN OF THE RED ALGA PORPHYRA PURPUREA (RHODOPHYTA) IS A NOVEL MEMBER OF THE CHYMOTRYPSIN FAMILY OF SERINE PROTEASES1

A complementary DNA (cDNA) clone from a Porphyra purpurea (Roth) C. Agardh sporophyte-specific subtracted cDNA library was found to encode a protein similar to serine proteases of the chymotrypsin class. The encoded protein contains a typical signal peptide and is particularly similar to chymotrypsins in the regions surrounding the active site residues and the activation site where cleavage of the propeptide occurs. In addition, the six cysteine residues characteristic of chymotrypsins are conserved. However, two of the three residues of the active site His/Asp/Ser charge relay triad have been replaced, indicating that the protein is unlikely to have peptidase activity. Northern hybridization confirmed that this cDNA is derived from an abundant, sporophyte-specific messenger RNA (mRNA). The presence of signal peptide on the encoded protein and the abundance of its mRNA suggested that this protein might be localized in the cell wall. Consequently, sporophyte cell walls were isolated and a major protein having a molecular weight similar to that estimated for the encoded protein was purified. N-terminal sequence analysis indicated that this cell wall protein is identical to that encoded by the cDNA with the amino terminus of the mature protein beginning at the activation site. This cell wall structural protein appears to have evolved from a chymotrypsin-like progenitor but has been adapted to bind cell wall proteins and/or polysaccharides rather than to cleave proteins.