Influence of development rate on pharyngeal teeth formula in <Emphasis Type="Italic">Abramis brama</Emphasis> (L.) bream: Experimental cata

An experiment on acceleration and retardation of ontogeny with thyroid manipulation has revealed direct changes in definitive dentition of pharyngeal bones in Abramis brama bream. As development rate accelerates, the number of teeth reduces to the formula 5-4. When development rate is retarded, this number increases to the formula 6-5. Moreover, an additional minor row of teeth (1.6–5.1, 2.6–5.2) is formed. The observed changes in tooth numbers exceed the known variability in natural populations of bream. It is assumed that heterochronies lead to the changes in the number of teeth.     

Significance of mirex-caused hypoglycemia and hyperlipidemia in rats

Treatment of rats with mirex (40 ppm in diet) caused hypoglycemia, liver enlargement, and inhibition of adrenal corticosteroid-synthesizing enzyme activity. At toxic dosages (20,000 ppm mirex in diet, which has a lethal toxicity-50 [LT-50] of ten days) poisoned female rats showed severe hypoglycemia, fatty liver, adrenal hyperplasia, hypophagia, lipid mobilization, and body weight (bw) loss. A 50 μg/kg intraperitoneal (IP) dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in male rats caused similar effects two days posttreatment. Hypoglycemia could be overcome by prednisone (which also inhibited adrenocorticoid-synthesizing enzyme activities) but not by streptozotocin treatment, indicating that hypoglycemia may be related to glucocorticoid deficiency resulting from inhibition of their synthesis and not by direct effects on pancreatic β-cells. Glucocorticoid deficiency could also cause increased release of adrenocorticoid hormone (ACTH), which may enhance fat mobilization caused by hypophagia.     

Mice Lacking Platelet-Derived Growth Factor D Display a Mild Vascular Phenotype

Platelet-derived growth factor D (PDGF-D) is the most recently discovered member of the PDGF family. PDGF-D signals through PDGF receptor β, but its biological role remains largely unknown. In contrast to other members of the PDGF family of growth factors, which have been extensively investigated using different knockout approaches in mice, PDGF-D has until now not been characterized by gene inactivation in mice. Here, we present the phenotype of a constitutive Pdgfd knockout mouse model (Pdgfd^-/-), carrying a LacZ reporter used to visualize Pdgfd promoter activity. Inactivation of the Pdgfd gene resulted in a mild phenotype in C57BL/6 mice, and the offspring was viable, fertile and generally in good health. We show that Pdgfd reporter gene activity was consistently localized to vascular structures in both postnatal and adult tissues. The expression was predominantly arterial, often localizing to vascular bifurcations. Endothelial cells appeared to be the dominating source for Pdgfd, but reporter gene activity was occasionally also found in subpopulations of mural cells. Tissue-specific analyses of vascular structures revealed that NG2-expressing pericytes of the cardiac vasculature were disorganized in Pdgfd^-/- mice. Furthermore, Pdgfd^-/- mice also had a slightly elevated blood pressure. In summary, the vascular expression pattern together with morphological changes in NG2-expressing cells, and the increase in blood pressure, support a function for PDGF-D in regulating systemic arterial blood pressure, and suggests a role in maintaining vascular homeostasis.     

Dimorphism in methane seep-dwelling ecotypes of the largest known bacteria

We present evidence for a dimorphic life cycle in the vacuolate sulfide-oxidizing bacteria that appears to involve the attachment of a spherical Thiomargarita-like cell to the exteriors of invertebrate integuments and other benthic substrates at methane seeps. The attached cell elongates to produce a stalk-like form before budding off spherical daughter cells resembling free-living Thiomargarita that are abundant in surrounding sulfidic seep sediments. The relationship between the attached parent cell and free-living daughter cell is reminiscent of the dimorphic life modes of the prosthecate Alphaproteobacteria, but on a grand scale, with individual elongate cells reaching nearly a millimeter in length. Abundant growth of attached Thiomargarita-like bacteria on the integuments of gastropods and other seep fauna provides not only a novel ecological niche for these giant bacteria, but also for animals that may benefit from epibiont colonization.     

Demonstrating the Potential for Dynamic Auditory Stimulation to Contribute to Motion Sickness

Auditory cues can create the illusion of self-motion (vection) in the absence of visual or physical stimulation. The present study aimed to determine whether auditory cues alone can also elicit motion sickness and how auditory cues contribute to motion sickness when added to visual motion stimuli. Twenty participants were seated in front of a curved projection display and were exposed to a virtual scene that constantly rotated around the participant''s vertical axis. The virtual scene contained either visual-only, auditory-only, or a combination of corresponding visual and auditory cues. All participants performed all three conditions in a counterbalanced order. Participants tilted their heads alternately towards the right or left shoulder in all conditions during stimulus exposure in order to create pseudo-Coriolis effects and to maximize the likelihood for motion sickness. Measurements of motion sickness (onset, severity), vection (latency, strength, duration), and postural steadiness (center of pressure) were recorded. Results showed that adding auditory cues to the visual stimuli did not, on average, affect motion sickness and postural steadiness, but it did reduce vection onset times and increased vection strength compared to pure visual or pure auditory stimulation. Eighteen of the 20 participants reported at least slight motion sickness in the two conditions including visual stimuli. More interestingly, six participants also reported slight motion sickness during pure auditory stimulation and two of the six participants stopped the pure auditory test session due to motion sickness. The present study is the first to demonstrate that motion sickness may be caused by pure auditory stimulation, which we refer to as “auditorily induced motion sickness”.     

The RAD6 DNA repair pathway in Saccharomyces cerevisiae: What does it do,and how does it do it?

The RAD6 pathway of budding yeast, Saccharomyces cerevisiae, is responsible for a substantial fraction of this organism's resistance to DNA damage, and also for induced mutagenesis. The pathway appears to incorporate two different recovery processes, both regulated by RAD6. The error-prone recovery prcess accounts for only a small amount of RAD6-dependent resistance, but probably all induced mutagenesis. The underlying mechanism, for error-prone recovery is very likely to be translesion synthesis. The error-free recovery process accounts for most of RAD6-dependent resistace, but its mechanism is less clear; it may entail error-free bypass by template switching and/or DNA gap filling by recombination. RAD6 regulates these activities by ubiquitinateins, and the roles they play in error-free and error-prone recovery, have not yet been established.     

The isolation and characterization of an alkylating-agent-sensitive yeast mutant, ngs1

We have isolated and characterized a mutant of baker's yeast, Saccharomyces cerevisiae, carrying the new mutation, ngs1, which is sensitive to the toxic effects of monofunctional alkylating agents, but normal with respect to 254-nm ultraviolet light sensitivity. ngs1 mutants exhibited more or less normal reversion frequencies for his1-7 and ilv1-92 induced by each of these mutagens. The various sensitivities associated with ngs1 cosegregated and have been shown to be the result of a lesion in a single nuclear gene. Extracts of ngs1 and NGS1+ strains contained approximately equal levels of an activity that removes 3-methyladenine (3MA) and 7-methylguanine (7MG) from DNA in vitro. The mutation also depressed sporulation.