Potential mechanisms of avian sex manipulation

The aim of this review is to consider the potential mechanisms birds may use to manipulate the sex of their progeny, and the possible role played by maternal hormones. Over the past few years there has been a surge of reports documenting the ability of birds to overcome the rigid process of chromosomal sex determination. However, while many of these studies leave us in little doubt that mechanisms allowing birds to achieve this feat do exist, we are only left with tantalizing suggestions as to what the precise mechanism or mechanisms may be. The quest to elucidate them is made no easier by the fact that a variety of environmental conditions have been invoked in relation to sex manipulation, and there is no reason to assume that any particular mechanism is conserved among the vast diversity of species that can achieve it. In fact, a number of intriguing proposals have been put forward. We begin by briefly reviewing some of the most recent examples of this phenomenon before highlighting some of the more plausible mechanisms, drawing on recent work from a variety of taxa. In birds, females are the heterogametic sex and so non-Mendelian segregation of the sex chromosomes could conceivably be under maternal control. Another suggestion is that follicles that ultimately give rise to males and females grow at different rates. Alternatively, the female might selectively abort embryos or 'dump lay' eggs of a particular sex, deny certain ova a chance of ovulation, fertilization or zygote formation, or selectively provision eggs so that there is sex-specific embryonic mortality. The ideas outlined in this review provide good starting points for testing the hypotheses both experimentally (behaviourally and physiologically) and theoretically.     

The Gap1 general amino acid permease acts as an amino acid sensor for activation of protein kinase A targets in the yeast Saccharomyces cerevisiae

Addition of a nitrogen source to yeast (Saccharomyces cerevisiae) cells starved for nitrogen on a glucose-containing medium triggers activation of protein kinase A (PKA) targets through a pathway that requires for sustained activation both a fermentable carbon source and a complete growth medium (fermentable growth medium induced or FGM pathway). Trehalase is activated, trehalose and glycogen content as well as heat resistance drop rapidly, STRE-controlled genes are repressed, and ribosomal protein genes are induced. We show that the rapid effect of amino acids on these targets specifically requires the general amino acid permease Gap1. In the gap1Delta strain, transport of high concentrations of l-citrulline occurs at a high rate but without activation of trehalase. Metabolism of the amino acids is not required. Point mutants in Gap1 with reduced or deficient transport also showed reduced or deficient signalling. However, two mutations, S391A and S397A, were identified with a differential effect on transport and signalling for l-glutamate and l-citrulline. Specific truncations of the C-terminus of Gap1 (e.g. last 14 or 26 amino acids) did not reduce transport activity but caused the same phenotype as in strains with constitutively high PKA activity also during growth with ammonium as sole nitrogen source. The overactive PKA phenotype was abolished by mutations in the Tpk1 or Tpk2 catalytic subunits. We conclude that Gap1 acts as an amino acid sensor for rapid activation of the FGM signalling pathway which controls the PKA targets, that transport through Gap1 is connected to signalling and that specific truncations of the C-terminus result in permanently activating Gap1 alleles.     

The isthmic organizer links anteroposterior and dorsoventral patterning in the mid/hindbrain by generating roof plate structures

During vertebrate development, an organizing signaling center, the isthmic organizer, forms at the boundary between the midbrain and hindbrain. This organizer locally controls growth and patterning along the anteroposterior axis of the neural tube. On the basis of transplantation and ablation experiments in avian embryos, we show here that, in the caudal midbrain, a restricted dorsal domain of the isthmic organizer, that we call the isthmic node, is both necessary and sufficient for the formation and positioning of the roof plate, a signaling structure that marks the dorsal midline of the neural tube and that is involved in its dorsoventral patterning. This is unexpected because in other regions of the neural tube, the roof plate has been shown to form at the site of neural fold fusion, which is under the influence of epidermal ectoderm derived signals. In addition, the isthmic node contributes cells to both the midbrain and hindbrain roof plates, which are separated by a boundary that limits cell movements. We also provide evidence that mid/hindbrain roof plate formation involves homeogenetic mechanisms. Our observations indicate that the isthmic organizer orchestrates patterning along the anteroposterior and the dorsoventral axis.     

Triton X-114 phase partitioning for the isolation of a pediocin-like bacteriocin from Carnobacterium divergens

A new procedure combining Triton X-114 phase partitioning and cation exchange chromatography was developed to purify a bacteriocin from a complex culture medium. This pediocin-like bacteriocin, secreted by Carnobacterium divergens and named divercin V41, was entirely recovered in the lower detergent-rich phase whereas all other substances (compounds from culture medium, bacterial metabolites) remained in the upper detergent-poor phase. Subsequent cation-exchange chromatography of the TX-114-rich phase allowed recovery of the pure active bacteriocin and also detergent removing. This new purification method is versatile, fast (only two steps) and can be carried out on whole broth.     

Steady-state tyrosine fluorescence to study the lipid-binding properties of a wheat non-specific lipid-transfer protein (nsLTP1)

The binding properties of a wheat non-specific lipid-transfer protein (nsLTP1) for different mono- and diacylated lipids was investigated. Lipids varied by their chain length, unsaturation and/or polar head group. In the case of fatty acid or lysophospholipid with a C10 chain length, no interaction can be measured, while poor affinity is reported for a C12 chain length. The dissociation constant (Kd) is about 0.5 microM independent of chain length from C14 to C18. The same affinity is obtained for C18 fatty acids with one or two unsaturations, whatever the cis-trans double bond isomery. In all cases, the number of binding sites, n, by protein ranges between 1.6 and 1.9, suggesting that two lipids can fit within the protein. omega-Hydroxy-palmitic acid, a natural monomer of cutin polymer, is found to interact with nsLTP1 with a Kd of 1 microM and n = 2. In contrast with previous data that reported the binding of the anionic diacylated phospholipid, DMPG (Sodano et al., FEBS Lett. 416 (1997) 130-134), nsLTP1 is not able to bind dimyristoylphosphatidylcholine, dimyristoylphosphatidic acid, palmitoyl-oleoylphosphatidylcholine or palmitoyl-oleoylphosphatidylglycerol added as liposomes or solubilized in ethanol. However, when both nsLTP1 and lipids are first solubilized in methanol, and then in the buffer, it was evidenced that the protein can bind these lipids. These results suggest that lipid-lipid interactions play an essential role in the binding process of plant nsLTP1 as previously mentioned for other lipid-transfer proteins.     

Stochastic modelling of environmental variation for biological populations

We examine stochastic effects, in particular environmental variability, in population models of biological systems. Some simple models of environmental stochasticity are suggested, and we demonstrate a number of analytic approximations and simulation-based approaches that can usefully be applied to them. Initially, these techniques, including moment-closure approximations and local linearization, are explored in the context of a simple and relatively tractable process. Our presentation seeks to introduce these techniques to a broad-based audience of applied modellers. Therefore, as a test case, we study a natural stochastic formulation of a non-linear deterministic model for nematode infections in ruminants, proposed by Roberts and Grenfell (1991). This system is particularly suitable for our purposes, since it captures the essence of more complicated formulations of parasite demography and herd immunity found in the literature. We explore two modes of behaviour. In the endemic regime the stochastic dynamic fluctuates widely around the non-zero fixed points of the deterministic model. Enhancement of these fluctuations in the presence of environmental stochasticity can lead to extinction events. Using a simple model of environmental fluctuations we show that the magnitude of this system response reflects not only the variance of environmental noise, but also its autocorrelation structure. In the managed regime host-replacement is modelled via periodic perturbation of the population variables. In the absence of environmental variation stochastic effects are negligible, and we examine the system response to a realistic environmental perturbation based on the effect of micro-climatic fluctuations on the contact rate. The resultant stochastic effects and the relevance of analytic approximations based on simple models of environmental stochasticity are discussed.     

Bacterial Community Dynamics during Start-Up of a Trickle-Bed Bioreactor Degrading Aromatic Compounds

This study was performed with a laboratory-scale fixed-bed bioreactor degrading a mixture of aromatic compounds (Solvesso100). The starter culture for the bioreactor was prepared in a fermentor with a wastewater sample of a car painting facility as the inoculum and Solvesso100 as the sole carbon source. The bacterial community dynamics in the fermentor and the bioreactor were examined by a conventional isolation procedure and in situ hybridization with fluorescently labeled rRNA-targeted oligonucleotides. Two significant shifts in the bacterial community structure could be demonstrated. The original inoculum from the wastewater of the car factory was rich in proteobacteria of the alpha and beta subclasses, while the final fermentor enrichment was dominated by bacteria closely related to Pseudomonas putida or Pseudomonas mendocina, which both belong to the gamma subclass of the class Proteobacteria. A second significant shift was observed when the fermentor culture was transferred as inoculum to the trickle-bed bioreactor. The community structure in the bioreactor gradually returned to a higher complexity, with the dominance of beta and alpha subclass proteobacteria, whereas the gamma subclass proteobacteria sharply declined. Obviously, the preceded pollutant adaptant did not lead to a significant enrichment of bacteria that finally dominated in the trickle-bed bioreactor. In the course of experiments, three new 16S as well as 23S rRNA-targeted probes for beta subclass proteobacteria were designed, probe SUBU1237 for the genera Burkholderia and Sutterella, probe ALBO34a for the genera Alcaligenes and Bordetella, and probe Bcv13b for Burkholderia cepacia and Burkholderia vietnamiensis. Bacteria hybridizing with the probe Bcv13b represented the main Solvesso100-degrading population in the reactor.Many branches of industry produce waste gases which contain odorous organic and inorganic components. Apart from the conventional thermal and physicochemical techniques for removal of pollutants from exhaust air, biological waste gas treatment is becoming more and more important. This kind of treatment is advantageous in cases in which the recovery of the components (e.g., absorption in liquids and adsorption in solids) or the utilization of a thermal process (thermal or catalytic combustion) is not economical. Today three different process variations for biological waste gas treatment are used: biofilters, bioscrubbers, and trickle-bed bioreactors. In biofilters and trickle-bed reactors, the pollutant-degrading microorganisms are immobilized on a carrier material, whereas in bioscrubbers the microorganisms are dispersed in the liquid phase. Biofilters and bioscrubbers are preferred in industry, while biofilters are common in compost production and sewage plants (10).Biological waste gas treatment has a long tradition. Already in 1953, a soil system was employed for the treatment of odorous sewer exhaust gases in Long Beach, Calif. (25), and although up to now a lot of efforts have been funneled into process engineering (14, 17, 18, 24), current knowledge of the involved microorganisms is still very limited. Diversity of the microbial communities in the bioreactors for the exhaust gas purification have mostly been analyzed by culture-dependent methods (9, 12, 28, 31). However, there is a large discrepancy between the total (direct) microscopic cell counts and viable plate counts in many ecosystems and every cultivation medium selects for certain microorganisms. Therefore, cultivation-based studies of bacterial populations may give wrong impressions of the actual community structure in an ecosystem (35). A possible means of avoiding qualitative and quantitative errors in the analysis of microbial community structure in complex ecosystems is the use of fluorescently labeled, rRNA-targeted oligonucleotides (5) for the in situ identification and enumeration of bacteria. This method has already been used successfully in complex microbial communities, such as multispecies biofilms (6, 22, 26), trickling filters (27), and activated sludge (37).The current study was performed with a laboratory-scale trickle-bed bioreactor degrading a mixture of aromatic compounds (Solvesso100). The starter culture for the inoculation of the bioreactor was an enrichment prepared in a fermentor which was itself started with a wastewater sample from a car painting factory as the inoculum and Solvesso100 as the sole carbon source. The goal of our study was to use for the first time fluorescent in situ hybridization (FISH) to investigate the microbial community structure and dynamics in the fermentor and the bioreactor during start-up. One of the open questions was whether the fermentor enrichment, which is done in suspension, indeed selects for those bacteria that later are immobilized in the bioreactor. In the course of this study, new 16S as well as 23S rRNA-targeted probes for phylogenetic groups within the beta subclass of the class Proteobacteria have been developed and applied in order to obtain a higher taxonomic resolution of the molecular techniques. The molecular data were compared to those obtained by traditional cultivation-dependent techniques.     

In-vitro germination and growth of lily pollen tubes is affected by protein phosphatase inhibitors

Inhibitors of type-2A protein phosphatase (PPase-2A), calyculin A (cal A) and okadaic acid (OA), inhibit pollen grain germination and growth of pollen tubes of Lilium longiflorum Thunb. at nanomolar concentrations. Half-maximal inhibition of cytoplasmic PPase-2A activity was below 0.1 nM for cal A and at 0.7 nM for OA. Other protein phosphatase inhibitors (tautomycin, cypermethrin, and dephostatin) were less effective. The OA- and cal A-sensitive as well as dephostatin-sensitive PPase activity in the cytoplasm did not change during germination and growth of pollen tubes. Addition of cal A and OA disturbed the direction of pollen tube growth and the distribution of cytoplasmic organelles and caused cell wall thickenings as observed by light and electron microscopy. Inhibition of PPase-2A caused multiple effects at the cellular level, cytoskeletal elements being a putative target of PPase-2A activity. Received: 30 March 1998 / Accepted: 6 July 1998     

Developmental control of H+/amino acid permease gene expression during seed development of Arabidopsis

Long distance transport of amino acids is mediated by several families of differentially expressed amino acid transporters. The two genes AAP1 and AAP2 encode broad specificity H⁺-amino acid co-transporters and are expressed to high levels in siliques of Arabidopsis, indicating a potential role in supplying the seeds with organic nitrogen. The expression of both genes is developmentally controlled and is strongly induced in siliques at heart stage of embryogenesis, shortly before induction of storage protein genes. Histochemical analysis of transgenic plants expressing promoter-GUS fusions shows that the genes have non-overlapping expression patterns in siliques. AAP1 is expressed in the endosperm and the cotyledons whereas AAP2 is expressed in the vascular strands of siliques and in funiculi. The endosperm expression of AAP1 during early stages of seed development indicates that the endosperm serves as a transient storage tissue for organic nitrogen. Amino acids are transported in both xylem and phloem but during seed filling are imported only via the phloem. AAP2, which is expressed in the phloem of stems and in the veins supplying seeds, may function in uptake of amino acids assimilated in the green silique tissue, in the retrieval of amino acids leaking passively out of the phloem and in xylem-to-phloem transfer along the path. The promoters provide excellent tools to study developmental, hormonal and metabolic control of nitrogen nutrition during development and may help to manipulate the timing and composition of amino acid import into seeds.