Zebrafish “personality” influences sensitivity to magnetic fields

How animals integrate different sensory information for orientation is a complex process involving interactions between a variety of internal and external factors. Due to this complexity, each component of a suite of factors is typically studied in isolation. Here, we examine how an internal factor (personality of fish) influences the response of zebrafish (Danio rerio) to the magnetic field, while swimming in a flow chamber. Our previous work demonstrated that the orientation to the water current (rheotaxis) of zebrafish individuals is influenced by variations of the magnetic field only when fish are part of a shoal. In this study, we evaluated the rheotactic behavior of 20 fish, grouped in shoals of “proactive” or “reactive” individuals, under magnetic fields of different directions. We found that the magnetic field influenced at which water speed rheotaxis was elicited in zebrafish with “reactive” personality, but not in those with “proactive” personality. These results suggest that fish personality influences response to or weighing of sensory inputs and provides some insight on the variation in behavioral responses to environmental stimuli in both laboratory and natural settings.     

Polyclonal origin of medullary carcinoma of the thyroid in multiple endocrine neoplasia type 2

Multiple endocrine neoplasia type 2 (MEN 2) is a dominantly inherited cancer syndrome characterized by medullary thyroid carcinoma (MTC) and other tumors. Since MTC can also occur in a sporadic form and as familial medullary thyroid carcinoma, this neoplasm offers a unique opportunity to investigate the difference of origin, if any, between the sporadic and the hereditary forms of a tumor. While sporadic malignancies have usually been found to result from a mutational event occurring at the single-cell level and are therefore monoclonal, studies on hereditary neoplasms have been scarce and often produced conflicting results. In order to determine the clonal origin of sporadic MTCs and of those occurring in MEN 2 syndromes we used a clonality assay based on a polymorphic trinucleotide repeat of the X-linked human androgen-receptor gene. We found that 10 out of 11 MTCs expressed a polyclonal pattern of X inactivation, including a significant percentage of the cases clinically defined as sporadic. Received: 21 May 1996 / Revised: 14 August 1996     

β-Amino acid residues: Conformational characterization of an N- and C-protected homo-β-(S)-leucine

Summary An N- and C-protected derivative ofhomo-β-leucine, Fmoc-homo-β-(S)-leucine methyl ester, synthesized from the corresponding proteinogenic parent α-amino acid in enantiopure form has been fully characterized in the solid state by X-ray diffraction analysis. The crystal conformation of this new residue indicates and extended conformation for thishomo-β-residue, with the ϕ torsion angle being more constrained than the μ and ψ angles.     

The Ecological Footprint Intensity of National Economies

At least three perspectives—industrial ecology (IE), ecological modernization theory (EMT), and the “environmental Kuznets curve” (EKC)—emphasize the potential for sustainability via refinements in production systems that dramatically reduce the environmental impacts of economic development. Can improvements in efficiency counterbalance environmental impacts stemming from the scale of production? To address this question we analyze cross‐national variation in the ecological footprint (EF) per unit of gross domestic product (GDP). The EF is a widely recognized indicator of human pressure on the environment. The EF of a nation is the amount of land area that would be required to produce the resources it consumes and to absorb the wastes it generates. The most striking finding of our analyses is that there is limited variation across nations in EF per unit of GDP. This indicates limited plasticity in the levels of EF intensity or eco‐efficiency among nations, particularly among affluent nations. EF intensity is lowest (ecoefficiency is highest) in affluent nations, but the level of efficiency in these nations does not appear to be of sufficient magnitude to compensate for their large productive capacities. These results suggest that modernization and economic development will be insufficient, in themselves, to bring about the ecological sustainability of societies.     

Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry for the Discrimination of Food-Borne Microorganisms

A methodology based on matrix-assisted laser desorption ionization-time of flight mass spectrometry of intact bacterial cells was used for rapid discrimination of 24 bacterial species, and detailed analyses to identify Escherichia coli O157:H7 were carried out. Highly specific mass spectrometric profiles of pathogenic and nonpathogenic bacteria that are well-known major food contaminants were obtained, uploaded in a specific database, and made available on the Web. In order to standardize the analytical protocol, several experimental, sample preparation, and mass spectrometry parameters that can affect the reproducibility and accuracy of data were evaluated. Our results confirm the conclusion that this strategy is a powerful tool for rapid and accurate identification of bacterial species and that mass spectrometric methodologies could play an essential role in polyphasic approaches to the identification of pathogenic bacteria.     

NUCLEAR FEATURES AND EFFECT OF NUTRIENTS ON GYMNODINIUM CATENATUM (DINOPHYCEAE) SEXUAL STAGES1

Gymnodinium catenatum Graham is an unarmored, cyst‐forming dinoflagellate species responsible for outbreaks of paralytic shellfish poisoning. The nuclear development of the cells during the sexual cycle and the effect of different nitrate and phosphate external levels on sexual stages were studied. Nuclear fusion of gametes occurred before or at the same time as cytoplasmic fusion. During this process, either both nuclei migrated to a central area in the sulcal region, or only one of them migrated to the other nucleus. The motile and longitudinally biflagellated zygote presented a large, pear‐shaped nucleus, and either divided or encysted. Planozygotes and germlings underwent similar division processes, which suggested an uncoordinated meiosis in both encysting and non‐encysting zygotes. Encystment in culture was greater under low nitrate and phosphate limitation (L/15) than when only one or neither of these nutrients were added (L‐N, L‐P, and ‐N‐P). However, planozygotes individually monitored achieved the maximum encystment (40%) in a medium with no phosphate or nitrate added (‐N‐P), while most of them divided (70%–90%) in replete (L1) or half‐replete (L‐N and L‐P) media. Low levels of nitrate in the medium of cyst formation promoted a deficient development of the cyst wall. On the other hand, low phosphate levels in the medium of germination prevented both planozygote and germling division and lowered the final germination frequencies of cysts. The minimum dormancy, with an average value of 13.7±5.5 days, was not affected by any of the nutritional conditions studied.     

MULTIPLE ROUTES OF SEXUALITY IN ALEXANDRIUM TAYLORI (DINOPHYCEAE) IN CULTURE1

Alexandrium taylori Balech is a cyst‐forming dinoflagellate species responsible for recurrent blooms in Mediterranean coastal waters. The nuclear development of the cells during the sexual cycle and the effect of different external nitrate and phosphate levels were studied. Nuclear fusion of gametes occurred 6–12 h after the complete cytoplasmic fusion. The U‐shaped nuclei fused through the end of one nucleus and the mid‐area of the other. The mobile and biflagellated zygote had a large, U‐shaped nucleus and may follow three different fates: direct division, short‐term encystment (ecdysal), and long‐term encystment (resting). Ecdysal cysts may divide in >24–96 h into two, four, six, or eight cells before germinating. Meiosis presumably occurred in three locations: in the planozygote, within the ecdysal cyst, and in the planomeiocyte (germling) liberated either from ecdysal or resting cysts. The effects of nutrients on these routes were studied in individually isolated sexual stages. (1) Direct divisions occurred mainly under replete conditions (L1), whereas no direct planozygote divisions were recorded in media with no phosphate added (L‐P). (2) Short‐term encystment was larger in media lacking phosphate (L‐P and L/30) than in medium with no nitrate added (L‐N) or under replete conditions (L1). (3) Long‐term encystment was only observed in medium with no nitrate added (L‐N). The long‐lived resting cyst, not previously described for this species, had a clear double wall, an irregular shape, a flat morphology, and a middle orange spot. No cysts germinated in 1–2 months, whereas 86% of the cysts germinated 2–3 months after being formed. A flow cytometry analysis showed that sexual induction and zygote formation were very fast and highly common processes, zygotes being nearly half of the population at days 3 and 5 after the induction of sexuality in the cultures.