Proneural genes and the specification of neural cell types

Certain morphological, physiological and molecular characteristics are shared by all neurons. However, despite these similarities, neurons constitute the most diverse cell population of any organism. Recently, considerable attention has been focused on identifying the molecular mechanisms that underlie this cellular diversity. Parallel studies in Drosophila and vertebrates have revealed that proneural genes are key regulators of neurogenesis, coordinating the acquisition of a generic neuronal fate and of specific subtype identities that are appropriate for the location and time of neuronal generation. These studies reveal that, in spite of differences between invertebrate and vertebrate neural lineages, Drosophila and vertebrate proneural genes have remarkably similar roles.     

Changes in jasmonate and gibberellin levels during development of potato plants (Solanum tuberosum)

Among the multiple environmental signals and hormonal factors regulatingpotato plant morphogenesis and controlling tuber induction, jasmonates (JAs)andgibberellins (GAs) are important components of the signalling pathways in theseprocesses. In the present study, with Solanum tuberosum L.cv. Spunta, we followed the endogenous changes of JAs and GAs during thedevelopmental stages of soil-grown potato plants. Foliage at initial growthshowed the highest jasmonic acid (JA) concentration, while in roots the highestcontent was observed in the stage of tuber set. In stolons at the developmentalstage of tuber set an important increase of JA was found; however, in tubersthere was no change in this compound during tuber set and subsequent growth.Methyl jasmonate (Me-JA) in foliage did not show the same pattern as JA; Me-JAdecreased during the developmental stages in which it was monitored, meanwhileJA increased during those stages. The highest total amount of JAs expressed asJA+Me-JA was found at tuber set. A very important peak ofJA in roots was coincident with that observed in stolons at tuber set. Also, aprogressive increase of this compound in roots was shown during the transitionof stolons to tubers. Of the two GAs monitored, gibberellic acid(GA₃) was the most abundant in all the organs. While GA₁and GA₃ were also found in stolons at the time of tuber set, noothermeasurements of GAs were obtained for stolons at previous stages of plantdevelopment. Our results indicate that high levels of JA and GAs are found indifferent tissues, especially during stolon growth and tuber set.     

Accumulation of fumonisins B1 and B2 in freshly harvested Brazilian commercial maize at three locations during two nonconsecutive seasons

Fifty-six Brazilian commercial maize cultivars were examined for FB1 and FB2 accumulation after two non-consecutive growing seasons. During the 94/95 growing season 35 cultivars were planted at three locations in the state of S?o Paulo, Brazil. All samples (total of 105) were contaminated (0.10 micro/g-6.58 microg/g FB1 and 0.04 microg/g-2.15 microg/g FB2). During the 97/98 growing season, 8 of the cultivars used during 94/95 and 21 others were replanted at the same locations. All 87 samples were contaminated (1.15 microg/g-43.80 microg/g FB1 and 0.08 microg/g-11.65 microg/g FB2). One cultivar accumulated significantly less fumonisins in all locations during both growing seasons, indicating that some degree of selection may be possible even in climates that favor F. moniliforme (verticillioides) infection of maize. The presence of water surplus in soil from kernel maturity to harvest correlated with concentrations of FB1 in the grain for the 8 cultivars planted during both seasons at three locations. Observed trends indicated that water excesses and deficits from silking to harvest increased fumonisin levels. The difference in the incidence of FB1, FB2, and FB1 + FB2 was significant between growing seasons, planting locations and between cultivars. Neither the level of hybridization, nor the type of endosperm, nor the length of the vegetative cycle showed any effect on the FB1 contamination.     

Intraspecific characterization of Vibrio alginolyticus isolates recovered from cultured fish in Spain

AIMS: Intraspecific differentiation and characterization of Vibrio alginolyticus strains isolated from cultured fish in Spain. MATERIALS AND RESULTS: Thirty-four Vibrio alginolyticus strains isolated from cultured fish were intraspecifically characterized on the basis of biochemical and exoenzymatic patterns, outer membrane protein (OMP) profiles, ribotyping and plasmid analyses. The typing methods used did not allow to group V. alginolyticus isolates on the basis of their sources of collection. A higher homogeneity was observed in OMP profiles. A high percentage of isolates were plasmidless. Ribotyping was the highest discriminatory typing method, as all the isolates tested presented 23 profiles using the HindIII restriction enzyme. On the basis of the ribotyping pattern, a similarity matrix and a dendrogram were constructed. CONCLUSIONS: The results obtained indicate that V. alginolyticus strains isolated from southwestern Spain belong to different clonal lineages. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has shown differences with other similar studies carried out in other areas of Europe with strains of V. alginolyticus with respect to the clonal lineages of the strains isolated in southwestern Spain.     

Detection of quorum sensing signals in the haloalkaliphilic archaeon Natronococcus occultus

Bacteria communicate at high cell density through quorum sensing, however, there are no reports about this mechanism in archaea. The archaeon Natronococcus occultus produces an extracellular protease at the end of growth. Early production of protease activity was observed when a low density culture was incubated with late exponential conditioned medium suggesting the presence of factor(s) inducing this activity. Conditioned medium and ethyl acetate extracts corresponding to the transition from exponential to stationary phase showed a positive signal in Agrobacterium biosensor. We report the detection of potential autoinducer molecules of the acylated homoserine lactone type in the archaeon N. occultus. These molecules may be responsible for the production/activation of extracellular protease.     

Mitosis under control

The mitotic checkpoint is essential to ensure accurate chromosome segregation by allowing a mitotic delay in response to a spindle defect. This checkpoint postpones the onset of anaphase until all the chromosomes are attached and correctly aligned onto the mitotic spindle. The checkpoint functions by preventing an ubiquitin ligase called the anaphase-promoting complex (APC) from ubiquitinylating proteins whose degradation is required for anaphase onset. Loss of this checkpoint results in chromosome missegregation in higher eukaryotes and may contribute to the genomic instability observed in most of the tumour cells.     

Variation in fruit and seed size from 38 wild populations of Phaseolus lunatus (Fabaceae) from Central Valley, Costa Rica

We studied the morfological diversity in fruits and seeds in 38 wild populations of Phaseolus lunatus var. lunatus (lima beans) in the central valley of Costa Rica. In order to do so, measured the length and width of the fruits and the length, width and thickness of seeds. We also calculated the ratio between these traits and determined the weight of 100 seeds. In general, we found significant variation between populations for all variables. When we grouped the 38 populations into eight geographical regions within the study area, we found significant differences between regions. However, the levels of variation between populations within geographical regions was larger than that found between geographical regions. These findings suggested that there is no clear relationship between these variables and the geographical grouping established in this study. The implications of these findings for the establishment of strategies for in situ conservation of wild populations of lima beans are discussed.     

Non-occlusal dental microwear variability in a sample of Middle and Late Pleistocene human populations from Europe and the Near East

Non-occlusal, buccal tooth microwear variability has been studied in 68 fossil humans from Europe and the Near East. The microwear patterns observed suggest that a major shift in human dietary habits and food processing techniques might have taken place in the transition from the Middle to the Late Pleistocene populations. Differences in microwear density, average length, and orientation of striations indicate that Middle Pleistocene humans had more abrasive dietary habits than Late Pleistocene populations. Both dietary and cultural factors might be responsible for the differences observed. In addition, the Middle Paleolithic Neanderthal specimens studied show a highly heterogeneous pattern of microwear when compared to the other samples considered, which is inconsistent with a hypothesis of all Neanderthals having a strictly carnivorous diet. The high density of striations observed in the buccal surfaces of several Neanderthal teeth might be indicative of the inclusion of plant foods in their diet. The buccal microwear variability observed in the Neanderthals is compatible with an overall exploitation of both plant and meat foods on the basis of food availability. A preliminary analysis of the relationship between buccal microwear density and climatic conditions prevailing in Europe during the Late Pleistocene has been attempted. Cold climatic conditions, as indicated by oxygen isotope stage data, seem to be responsible for higher densities of microwear features, whereas warmer periods could correspond to a reduced pattern of scratch density. Such a relationship would be indicative of less abrasive dietary habits, perhaps more meat dependent, during warmer periods.     

Temporal localization of porcine reproductive and respiratory syndrome virus in reproductive tissues of experimentally infected boars

Porcine reproductive and respiratory syndrome virus (PRRSV) has been reported to be shed in the semen of infected boars. To determine whether the reproductive tissues could be a persistent source of virus and the possible origin of PRRSV found in semen of infected boars, 20 PRRSV-seronegative boars were intranasally inoculated with 5 x 10(6) median tissue culture infective doses (TCID50) of PRRSV and necropsied at different times post-inoculation (p.i.) from Day 2 to Day 37 p.i. Blood samples were collected before experimental inoculation, at necropsy and at different times p.i. At necropsy, epididymal semen and reproductive tissues were collected and the presence of the virus determined by virus isolation. The infection of the boars was demonstrated by the isolation of the virus from the sera of all inoculated boars and by seroconversion. PRRSV was detected in serum samples from Day 2 to Day 23 p.i., although the viremic period was largely dependent on the individual response to infection. Viral replication was proven within different reproductive tissues from Day 2 to Day 23 p.i., being most consistently found in the epididymus. In addition, PRRSV was isolated in semen from Day 4 to Day 10 p.i. The correlation of a diminished viremia and the inability to isolate PRRSV from semen or reproductive tissues may be due to one of two possibilities. First, viremia is responsible for most of the virus isolated from reproductive tissues due to the movement of PRRSV-infected cells out of the blood and into the tissues. Second, viremia may initially seed the reproductive tissues with PRRSV, and then the virus is produced into the reproductive tract and shed into semen at low levels.     

Epifluorescence microscope methods for bacterial enumeration in a 4-chlorophenol degrading consortium

Epifluorescence microscope methods, namely BacLight, direct epifluorescence filter technique and Rhodamine 123, consistently underestimated plate bacterial counts in a 4-chlorophenol degrading consortium. Cells capable of passing through 0.2 microm filters, referred as 'ultramicrocells', were found. Although cell counts were higher when traditional methods were used, BacLight and direct epifluorescence filter technique were convenient techniques for the systematic monitoring of bacteria involved in biodegradation processes, as results were consistent and available within a short time.