Variable region V1 ofSaccharomyces cerevisiae 18S rRNA participates in biogenesis and function of the small ribosomal subunit

The role of helix 6, which forms the major portion of the most 5′-located expansion segment ofSaccharomyces cerevisiae 18S rRNA, was studied by in vivo mutational analysis. Mutations that increased the size of the helical part and/or the loop, even to a relatively small extent, abolished 18S rRNA formation almost completely. Concomitantly, 35S pre-rRNA and an abnormal 23S precursor species accumulated. rDNA units containing these mutations did not support cell growth. A deletion removing helix 6 almost completely, on the other hand, had a much less severe effect on the formation of 18S rRNA, and cells expressing only the mutant rRNA remained able to grow, albeit at a much reduced rate. Disruption of the apical A·U base pair by a single point mutation did not cause a noticeable reduction in the level of 18S rRNA but did result in a twofold lower growth rate of the cells. This effect could not be reversed by introduction of a second point mutation that restores base pairing. We conclude that both the primary and the secondary structure of helix 6 play an important role in the formation and the biological function of the 40S subunit. Edited by: S.A. Gerbi     

Differential β- and α-adrenergic activation during psychological stress

The responsivity of several cardiovascular indices to a computerized mental arithmetic stress and a cold pressor stress were investigated in 22 healthy adult subjects. The major findings were that the largely β-adrenergically driven T-wave amplitude, pre-ejection period, R-wave to pulse interval, and left ventricular ejection time values responded only to mental arithmetic; a significant decrease in cardiac output and increase in peripheral resistance were elicited during the cold pressor test; inter-beat-interval and subjective stress ratings responded significantly to both stresses compared to baseline levels, but more intensely to mental arithmetic than the cold pressor test; blood pressure, stroke volume and the maximum of the first derivative of the raw impedance signal responded unspecifically to both stresses. These findings support the idea that cardiovascular responses to psychological challenge depend on the level of cognitive processing required for the task. In addition, the superfluity of multiple variable measurements to study cardiovascular reactivity in such situations is discussed. Accepted: 3 September 1996     

Isolation and characterization of the mating-type locus of the barley pathogen Pyrenophora teres and frequencies of mating-type idiomorphs within and among fungal populations collected from barley landraces.

Pyrenophora teres f. sp. teres mating-type genes (MAT-1: 1190 bp; MAT-2: 1055 bp) have been identified. Their predicted proteins, measuring 379 and 333 amino acids, respectively, are similar to those of other Pleosporales, such as Pleospora sp., Cochliobolus sp., Alternaria alternata, Leptosphaeria maculans, and Phaeosphaeria nodorum. The structure of the MAT locus is discussed in comparison with those of other fungi. A mating-type PCR assay has also been developed; with this assay we have analyzed 150 isolates that were collected from 6 Sardinian barley landrace populations. Of these, 68 were P. teres f. sp. teres (net form; NF) and 82 were P. teres f. sp. maculata (spot form; SF). Within each mating type, the NF and SF amplification products were of the same length and were highly similar in sequence. The 2 mating types were present in both the NF and the SF populations at the field level, indicating that they have all maintained the potential for sexual reproduction. Despite the 2 forms being sympatric in 5 fields, no intermediate isolates were detected with amplified fragment length polymorphism (AFLP) analysis. These results suggest that the 2 forms are genetically isolated under the field conditions. In all of the samples of P. teres, the ratio of the 2 mating types was consistently in accord with the 1:1 null hypothesis. This ratio is expected when segregation distortion and clonal selection among mating types are absent or asexual reproduction is rare. Overall, sexual reproduction appears to be the major process that equalizes the frequencies of the 2 mating types within populations.     

MOL1 is required for cambium homeostasis in Arabidopsis

Plants maintain pools of pluripotent stem cells which allow them to constantly produce new tissues and organs. Stem cell homeostasis in shoot and root tips depends on negative regulation by ligand–receptor pairs of the CLE peptide and leucine‐rich repeat receptor‐like kinase (LRR‐RLK) families. However, regulation of the cambium, the stem cell niche required for lateral growth of shoots and roots, is poorly characterized. Here we show that the LRR‐RLK MOL1 is necessary for cambium homeostasis in Arabidopsis thaliana. By employing promoter reporter lines, we reveal that MOL1 is active in a domain that is distinct from the domain of the positively acting CLE41/PXY signaling module. In particular, we show that MOL1 acts in an opposing manner to the CLE41/PXY module and that changing the domain or level of MOL1 expression both result in disturbed cambium organization. Underlining discrete roles of MOL1 and PXY, both LRR‐RLKs are not able to replace each other when their expression domains are interchanged. Furthermore, MOL1 but not PXY is able to rescue CLV1 deficiency in the shoot apical meristem. By identifying genes mis‐expressed in mol1 mutants, we demonstrate that MOL1 represses genes associated with stress‐related ethylene and jasmonic acid hormone signaling pathways which have known roles in coordinating lateral growth of the Arabidopsis stem. Our findings provide evidence that common regulatory mechanisms in different plant stem cell niches are adapted to specific niche anatomies and emphasize the importance of a complex spatial organization of intercellular signaling cascades for a strictly bidirectional tissue production.     

MiRNA-21 Expression Decreases from Primary Tumors to Liver Metastases in Colorectal Carcinoma

Objective

Metastasis is the major cause of death in colorectal cancer patients. Expression of certain miRNAs in the primary tumors has been shown to be associated with progression of colorectal cancer and the initiation of metastasis. In this study, we compared miRNA expression in primary colorectal cancer and corresponding liver metastases in order to get an idea of the oncogenic importance of the miRNAs in established metastases.

Methods

We analyzed the expression of miRNA-21, miRNA-31 and miRNA-373 in corresponding formalin-fixed paraffin-embedded (FFPE) tissue samples of primary colorectal cancer, liver metastasis and healthy tissues of 29 patients by quantitative real-time PCR.

Results

All three miRNAs were significantly up-regulated in the primary tumor tissues as compared to healthy colon mucosa of the respective patients (p < 0.01). MiRNA-21 and miRNA-31 were also higher expressed in liver metastases as compared to healthy liver tissues (p < 0.01). No significant difference of expression of miRNA-31 and miRNA-373 was observed between primary tumors and metastases. Of note, miRNA-21 expression was significantly reduced in liver metastases as compared to the primary colorectal tumors (p < 0.01).

Conclusion

In the context of previous studies demonstrating increased miRNA-21 expression in metastatic primary tumors, our findings raise the question whether miRNA-21 might be involved in the initiation but not in the perpetuation and growth of metastases.     

Two models for screening chelating agents for cadmium removal

The effectiveness of some chelating agents to mobilize cadmium from Chinese hamster ovary cells after chronic exposure (20 hr), as well as from cytosolic metallothionein, was studied. In the first protocol, the most effective substance was 2,3-dimercaptopropanol, followed by 2,3-dimercaptopropane-1-sulfonate and 2,3-dimercaptosuccinic acid, whereas CaNa₃3-diethylenetriamine pentaacetic acid × 5H₂O showed less effect. Simultaneous incubation of cells with cadmium and the chelating agent resulted in a different order of effectiveness: CaNa₃ DTPA prevented cadmium uptake almost totally, 2,3-mercaptopropanol by 75% and 2,3-dimercaptopropane-1-sulfonate by 35%. Neither CaNa₃-diethylenetriamine pentaacetic acid × 5H₂O nor 2,3-dimercaptosuccinic acid had altered the distribution of cadmium between the cytosolic protein fractions after a 2 hr incubation of cells, whereas after this period, 2,3-dimercaptopropanol had removed all cadmium from metallothionein, and 2,3-dimercaptopropane-1-sulfonate about 50%. None of the chelating agents had reduced the amount of Cd bound to high molecular weight proteins. In the cell free system, 2,3-dimercaptopropanol and 2,3-dimercaptopropane-1-sulfonate were equally effective and removed all cadmium from metallothionein within ten minutes. CaNa₃-diethylenetriamine pentaacetic acid × 5H₂O, however, even after 60 min, had removed only 50% of the cadmium. The remaining cadmium was found distributed to the high molecular weight and lower molecular weight protein fractions.Abbreviations BAL 2,3-dimercaptopropanol - CHO Chinese hamster ovary cells - DMPS 2,3-dimercaptopropane-1-sulfonate - DMSA 2,3-dimercaptosuccinic acid - DTPA CaNa₃-diethylenetriaminepentaacetic acid × 5 H₂O - HMW proteins high molecular weight proteins - MT metallothionein     

Resource partitioning of sonar frequency bands in rhinolophoid bats

Summary In the Constant Frequency portions of the orientation calls of various Rhinolophus and Hipposideros species, the frequency with the strongest amplitude was studied comparatively. (1) In the five European species of the genus Rhinolophus call frequencies are either species-specific (R. ferrumequinum, R. blasii and R. euryale) or they overlap (R. hipposideros and R. mehelyi). The call frequency distributions are approximately 5–9 kHz wide, thus their ranges spead less than ±5% from the mean (Fig. 1). Frequency distributions are considerably narrower within smaller geographic areas. (2) As in other bat groups, call frequencies of the Rhinolophoidea are negatively correlated with body size (Fig. 3). Regression lines for the genera Rhinolophus and Rhinolophus, species from dryer climates have on the average higher call frequencies than species from tropical rain forests. (4) The Krau Game Reserve, a still largely intact rain forest area in Malaysia, harbours at least 12 syntopic Rhinolophus and Hipposiderso species. Their call frequencies lie between 40 and 200 kHz (Fig. 2). Distribution over the available frequency range is significantly more even than could be expected from chance alone. Two different null hypotheses to test for random character distribution were derived from frequency-size-relations and by sampling species assemblages from a species pool (Monte Carlo method); both were rejected. In particular, call frequencies lying close together are avoided (Figs. 4, 5). Conversely, the distribution of size ratios complied with a corresponding null hypothesis. This even distribution may be a consequence of resource partitioning with respect to prey type. Alternatively, the importance of these calls as social signals (e.g. recognition of conspecifics) might have necessitated a communication channel partitioning.     

The effects of Plagiorchis noblei metacercariae on the development and survival of Aedes aegypti larvae in the laboratory

Plagiorchis noblei infections impair the survival and development of fourth instar Aedes aegypti larvae. Mortality during the larval and pupal stages reached 92%, and 60% of the emerging adults were malformed. The metacercariae interfere with pupation and the emergence of adults. Larvae and pupae that fail to transform to the next developmental stage within the normal time characteristically persist for extended periods, but invariably die without transforming. Whereas 82% of the control larvae gave rise to functional adults, only 4% of infected larvae managed to do so. Such effects may facilitate the transmission of the parasite.