The gene coding for the α1 subunit of the skeletal dihydropyridine receptor (Cchl1a3=mdg) maps to mouse Chromosome 1 and human 1q32

Using both chromosomal in situ hybridization and molecular techniques, we report the genetic localization of the gene coding for the alpha 1 subunit of the skeletal slow Ca²⁺ current channel/DHP receptor gene (Cchl1a3) on human Chromosome (Chr) 1 (1q31–1q32 region) and on mouse Chr 1 region (F-G). On the basis of single-strand conformation polymorphism (SSCP-PCR) analysis in an interspecific backcross, we have determined that the Cchl1a3=mdg (muscular dysgenesis) locus is very closely linked to the myogenin (Myog) locus.     

Can the biotic nestedness matrix be used predictively?

The biotas of a suite of neighboring patches of remnant vegetation often form a series of nested sub-sets, in which the species present in species-poor patches are non-random sub-sets of those present in richer patches. There has been recent interest in ways in which this knowledge may be used to aid conservation. We focus here on whether nested patterns can be used predictively. If nestedness in a fragmented system increases over time through biotic relaxation, locations where particular species may become extinct or are likely to colonize might be predictable and this could be useful in threatened-species management. We used the Temperature Calculator of Atmar and Patterson (1995) to arrange a matrix of bird species' occurrences in a series of buloke Allocasuarina leuhmannii woodland remnants so that nestedness was maximized. Probability bands generated by the calculator were used to predict possible colonization and extinction events. We then re-surveyed the avifauna of the fragments after a seven-year interval to test these predictions. Although nestedness increased between the two survey periods, there was no linear relationship between the generated probability of extinctions or colonizations and the accuracy of the predictions. The predictions derived from the calculator were no more accurate than a second set of predictions generated by use of a simple non-nested model. Despite the increase in nestedness, the arrangement of sites in each of the two maximally packed matrices was substantially different. For the nestedness matrix to generate accurate predictions, an increase in nestedness must be due to a minimization of unexpected species presences and absences rather than an extensive redistribution of species among remnants, as we found. The potential utility of nested patterns in predicting systematic colonization and extinction events should be further evaluated in other, less dynamic, fragmented systems such as those undergoing biotic relaxation.     

Endothelin Stimulates Phospholipase D in Striatal Astrocytes

Abstract: In primary cultures of mouse striatal astrocytes prelabeled with [³H]myristic acid, endothelin (ET)-1 induced a time-dependent formation of [³H]phosphatidic acid and [³H]diacylglycerol. In the presence of ethanol, a production of [³H]phosphatidylethanol was observed, indicating the activation of a phospholipase D (PLD). ET-1 and ET-3 were equipotent in stimulating PLD activity (EC₅₀ = 2–5 n M ). Pretreatment of the cells with pertussis toxin partially abolished the effect of ET-1, indicating the involvement of a G_i/G_o protein. Inhibition of protein kinase C by Ro 31-8220 or down-regulation of the kinase by a long-time treatment with phorbol 12-myristate 13-acetate (PMA) totally abolished the ET-1-induced stimulation of PLD. In contrast, a cyclic AMP-dependent process is not involved in the activation of PLD, because the ET-1-evoked formation of [³H]phosphatidylethanol was not affected when cells were coincubated with either isoproterenol, 8-bromo-cyclic AMP, or forskolin. Acute treatment with PMA also stimulated PLD through a protein kinase C-dependent process. However, the ET-1 and PMA responses were additive. Furthermore, the ET-1-evoked response, contrary to that of PMA, totally depended on the presence of extracellular calcium. These results suggest that at least two distinct mechanisms are involved in the control of PLD activity in striatal astrocytes. Finally, ET-1, ET-3, and PMA also stimulated PLD in astrocytes from the mesencephalon, the cerebral cortex, and the hippocampus.     

Modeling the population dynamics of annual plants with seed bank and density dependent effects

A model is proposed for the population dynamics of an annual plant (Sesbania vesicaria) with a seed bank (i.e. in which a proportion of seeds remain dormant for at least one year). A simple linear matrix model is deduced from the life cycle graph. The dominant eigenvalue of the projection matrix is estimated from demographic parameters derived from field studies. The estimated values for population growth rate () indicates that the study population should be experiencing a rapid exponential increase, but this was not the case in our population.The addition of density dependent effects on seedling survivorship and adult fecundity, effects for which field studies provide evidence, considerably improves our model. Depending on the demographic parameters, the model leads to stable equilibrium, oscillations, or chaos. Study of the behaviour of this model in the parameter space shows that the existence of a seed bank allows higher among-year variation of adult fecundity, without leaving the region of demographic stability. Field data obtained over 3 years confirm this prediction.     

Kinetics of induction of error-prone repair of bacteriophage lambda by temperature shift in an Escherichia coli dnaB mutant.

Summary Preincubation at 42^o, before infection at permissive temperature by phage , of an Escherichia coli dnaB mutant, provokes a significant increase in survival and mutagenesis of ultraviolet irradiated phage as well as mutagenesis of untreated phage. Similarly to UV irradiation and many chemical mutagens, the inhibition of DNA synthesis by temperature shift of this dnaB mutant induces SOS repair. This work shows that replication blockage in bacterial DNA is not only mutagenic for bacterial DNA itself (Witkin, 1975) but also for normally replicating DNA, probably due to induction of diffusible products.     

Variations in oxygen consumption of Demidoff's bushbaby (Galago demidovii, lorisidae, primates) in captivity

Summary In captivity,Galago demidovii shows annual variations in oxygen consumption which are independent of daylength cycles. This rhythm is characterized by two periods during which metabolic and sexual activities are increased: a short period in November/December; and a longer period from March to June inclusive. These two periods alternate with periods of decreased metabolic rate, of which the most pronounced extends from July to September. Another point of interest is that the basal metabolism of captive Galagos is 17.5% above the value calculated from its body weight.The physiological cycle observed in captivity is synchronized with climatic variations in Makokou (Gaboon), from where the animals originated: higher metabolic and sexual activities are correlated with rainy seasons. This study suggests that an endogenous rhythm may exist inGalago demidovii.     

Le prétendu rhinocéros de Nouvelle Calédonie est un marsupial (Zygomaturus diahotensis nov. sp.): Solution d'une énigmeet conséquences paléogéographiques

The first mammalian remain ever found in NewCaledonia is an upper tooth found by golddiggers in the Plio-Pleistocene terrace from the Diahot river. This tooth, given to the Muséum national d'Histoire naturelle (Paris) in 1876, was determined as a rhinoceros tooth and then completely forgotten. Its detailed study shows that it belongs to Zygomaturus, a large marsupial diprotodontid genus whose story is rather complicated. The Diahot tooth represents a new species of Zygomaturus, Z. diahotensis nov. sp., close to Z. trilobus from the Australian Pleistocene. That kinship suggests a Plio-Pleistocene land connection between Australia and New Caledonia, whereas till now New Caledonia was supposed to be separated from Australia since the end of the Cretaceous, because of the total absence of indigenous mammals, fossil or recent, in New Caledonia. The latest geological studies in the East Pacific do not contradict our hypothesis.     

Modular bioreactor for primary human hepatocyte culture: medium flow stimulates expression and activity of detoxification genes

Down-regulation of detoxification genes, notably cytochrome P450 (CYPs), in primary hepatocyte cultures is a long-standing and major concern. We evaluated the influence of medium flow in this model. Hepatocytes isolated from 12 different liver donors were cultured either in a multichamber modular bioreactor (MCmB, flow rate 250-500 μL/min) or under standard/static conditions, and the expression of 32 genes, enzyme activities and biological parameters were measured 7-21 days later. mRNA expression of genes involved in xenobiotic/drug metabolism and transport, including CYP1A1, 1A2, 2B6, 2C9, 3A4 (and activities for some of them), UDP-glucuronosyltransferase (UGT) 1A1, UGT2B4, UGT2B7, glutathione S-transferase (GSTα), and multidrug resistance protein 1 (MDR1) and MRP2, were specifically up-regulated by medium flow as compared with static controls in all cultures tested. In 2-week-old cultures, expression of detoxification genes reached levels close to or higher than those measured in freshly isolated hepatocytes. In contrast, CYP2D6 and most of other tested genes were not affected by medium flow. We conclude that medium flow specifically interferes with, and up-regulates, the activity of xenosensors and/or the expression of detoxification genes in primary human hepatocytes. Down-regulation of detoxification genes in conventional (static) cultures is therefore partly a consequence of the absence of medium circulation.     

Three-dimensional gas exchange pathways in pome fruit characterized by synchrotron x-ray computed tomography

Our understanding of the gas exchange mechanisms in plant organs critically depends on insights in the three-dimensional (3-D) structural arrangement of cells and voids. Using synchrotron radiation x-ray tomography, we obtained for the first time high-contrast 3-D absorption images of in vivo fruit tissues of high moisture content at 1.4-microm resolution and 3-D phase contrast images of cell assemblies at a resolution as low as 0.7 microm, enabling visualization of individual cell morphology, cell walls, and entire void networks that were previously unknown. Intercellular spaces were always clear of water. The apple (Malus domestica) cortex contains considerably larger parenchyma cells and voids than pear (Pyrus communis) parenchyma. Voids in apple often are larger than the surrounding cells and some cells are not connected to void spaces. The main voids in apple stretch hundreds of micrometers but are disconnected. Voids in pear cortex tissue are always smaller than parenchyma cells, but each cell is surrounded by a tight and continuous network of voids, except near brachyssclereid groups. Vascular and dermal tissues were also measured. The visualized network architecture was consistent over different picking dates and shelf life. The differences in void fraction (5.1% for pear cortex and 23.0% for apple cortex) and in gas network architecture helps explain the ability of tissues to facilitate or impede gas exchange. Structural changes and anisotropy of tissues may eventually lead to physiological disorders. A combined tomography and internal gas analysis during growth are needed to make progress on the understanding of void formation in fruit.