Defects in the cytochrome b6/f complex prevent light-induced expression of nuclear genes involved in chlorophyll biosynthesis

Mutants with defects in the cytochrome (cyt) b6/f complex were analyzed for their effect on the expression of a subgroup of nuclear genes encoding plastid-localized enzymes participating in chlorophyll biosynthesis. Their defects ranged from complete loss of the cytb6/f complex to point mutations affecting specifically the quinone-binding QO site. In these seven mutants, light induction of the tetrapyrrole biosynthetic genes was either abolished or strongly reduced. In contrast, a normal induction of chlorophyll biosynthesis genes was observed in mutants with defects in photosystem II, photosystem I, or plastocyanin, or in wild-type cells treated with 3-(3'4'-dichlorophenyl)-1,1-dimethylurea or 2,5-dibromo-3-methyl-6-isopropyl benzoquinone. We conclude that the redox state of the plastoquinone pool does not control light induction of these chlorophyll biosynthetic genes. The signal that affects expression of the nuclear genes appears to solely depend on the integrity of the cytb6/f complex QO site. Since light induction of these genes in Chlamydomonas has recently been shown to involve the blue light receptor phototropin, the results suggest that cytb6/f activity regulates a plastid-derived factor required for their expression. This signaling pathway differs from that which regulates state transitions, since mutant stt7, lacking a protein kinase involved in phosphorylation of the light-harvesting complex II, was not altered in the expression of the chlorophyll biosynthetic genes.     

Ferruginous pygmy-owl (Glaucidium brasilianum) and eastern screech-owl (Megascopes asio): new hosts for Philornis mimicola (Diptera: Muscidae) and Ornithodoros concanensis (Acari: Argasidae)

While banding ferruginous pygmy-owls (Glaucidium brasilianum) and Eastern screech-owls (Megascops asio) in south Texas during 2004, we recorded Philornis mimicola (Diptera: Muscidae) and Ornithodoros concanensis (Acari: Argasidae) parasitizing nestlings. Inspection of nestlings revealed 54 P. mimicola and one O. concanensis. Inspection of nest material revealed 111 P. mimicola, including 57 puparia. The effect (e.g., blood loss, anemia) of these hematophagous parasites might have contributed to the demise of at least one Eastern screech-owl nestling. This is the first record of P. mimicola and O. concanensis parasitizing ferruginous pygmy-owls and Eastern screech-owls.     

Noise-Induced Coherence and Network Oscillations in a Reduced Bursting Model

The dynamics of the Hindmarsh-Rose (HR) model of bursting thalamic neurons is reduced to a system of two linear differential equations that retains the subthreshold resonance properties of the HR model. Introducing a reset mechanism after a threshold crossing, we turn this system into a resonant integrate-and-fire (RIF) model. Using Monte-Carlo simulations and mathematical analysis, we examine the effects of noise and the subthreshold dynamic properties of the RIF model on the occurrence of coherence resonance (CR). Synchronized burst firing occurs in a network of such model neurons with excitatory pulse-coupling. The coherence level of the network oscillations shows a stochastic resonance-like dependence on the noise level. Stochastic analysis of the equations shows that the slow recovery from the spike-induced inhibition is crucial in determining the frequencies of the CR and the subthreshold resonance in the original HR model. In this particular type of CR, the oscillation frequency strongly depends on the intrinsic time scales but changes little with the noise intensity. We give analytical quantities to describe this CR mechanism and illustrate its influence on the emerging network oscillations. We discuss the profound physiological roles this kind of CR may have in information processing in neurons possessing a subthreshold resonant frequency and in generating synchronized network oscillations with a frequency that is determined by intrinsic properties of the neurons. PACS 05.45.-a, 05.40.Ca, 87.18.Sn, 87.19     

New regioselective derivatives of sucrose with amino acid and acrylic groups

We report here a range of new sucrose derivatives obtained from '3-ketosucrose' in aqueous medium with few reaction steps. As an intermediate, 3-amino-3-deoxy-alpha-D-allopyranosyl beta-D-fructofuranoside (1) was obtained via the classical route of reductive amination with much improved yield and high stereoselectivity. Building blocks for polymerization were synthesized by introduction of acrylic-type side chains, for example, with methacrylic anhydride. Corresponding polymers were synthesized. Aminoacyl and peptide conjugates were obtained through conventional peptide synthesis with activated and protected amino acids. Deprotection yielded new glycoderivatives having an unconventional substitution pattern, namely 3-(aminoacylamino) allosaccharides. Both mono- and di-peptide conjugates of allosucrose have been synthesized.     

The K-Ras 4A isoform promotes apoptosis but does not affect either lifespan or spontaneous tumor incidence in aging mice

Ras proteins function as molecular switches in signal transduction pathways, and, here, we examined the effects of the K-ras4A and 4B splice variants on cell function by comparing wild-type embryonic stem (ES) cells with K-ras(tmDelta4A/tmDelta4A) (exon 4A knock-out) ES cells which express K-ras4B only and K-ras(-/-) (exons 1-3 knock-out) ES cells which express neither splice variant, and intestinal epithelium from wild-type and K-ras(tmDelta4A/tmDelta4A) mice. RT-qPCR analysis found that K-ras4B expression was reduced in K-ras(tmDelta4A/tmDelta4A) ES cells but unaffected in small intestine. K-Ras deficiency did not affect ES cell growth, and K-Ras4A deficiency did not affect intestinal epithelial proliferation. K-ras(tmDelta4A/tmDelta4A) and K-ras(-/-) ES cells showed a reduced capacity for differentiation following LIF withdrawal, and K-ras(-/-) cells were least differentiated. K-Ras4A deficiency inhibited etoposide-induced apoptosis in ES cells and intestinal epithelial cells. However, K-ras(tmDelta4A/tmDelta4A) ES cells were more resistant to etoposide-induced apoptosis than K-ras(-/-) cells. The results indicate that (1) K-Ras4A promotes apoptosis while K-Ras4B inhibits it, and (2) K-Ras4B, and possibly K-Ras4A, promotes differentiation. The findings raise the possibility that alteration of the K-Ras4A/4B isoform ratio modulates tumorigenesis by differentially affecting stem cell survival and/or differentiation. However, K-Ras4A deficiency did not affect life expectancy or spontaneous overall tumor incidence in aging mice.     

Genomewide evolutionary rates in laboratory and wild yeast

As wild organisms adapt to the laboratory environment, they become less relevant as biological models. It has been suggested that a commonly used S. cerevisiae strain has rapidly accumulated mutations in the lab. We report a low-to-intermediate rate of protein evolution in this strain relative to wild isolates.     

The response of the natriuretic peptide system to water deprivation in the desert rodent, Notomys alexis

Natriuretic peptides (NPs) are regulatory molecules that cause cGMP-mediated diuresis and natriuresis in mammals. Accordingly, it is interesting to consider their role in desert-adapted animals in which water is often limited. This study investigated the response of the natriuretic peptide (NP) system to varying periods of water deprivation (WD) in the Australian desert rodent species, Notomys alexis. It was hypothesised that the expression of the NP system will be down-regulated in water-deprived N. alexis compared to water-replete animals. The plasma levels of ANP were significantly reduced after 3 days of WD, but were unaffected by 7, 14 and 28 days of WD. Water deprivation for 3, 7, 14 days had a variable effect on the mRNA expression of ANP, CNP, NPR-A, NPR-B, and NPR-C, and a uniform down-regulation was not observed. However, after 28 days of WD, mRNA expression was similar to water-replete animals, except for NPR-A. Surprisingly, 7 and 14 days of WD caused an up-regulation in the ability of ANP to stimulate cGMP; this also occurred at 14 days for CNP. Taken together, the mRNA expression and peptide mediated guanylyl cyclase activity data after WD were in the opposite direction to what was predicted. Interestingly, after 28 days of WD, most parameters were similar to those of water-replete animals, which indicates that a down-regulation of the NP system is not part of the physiological response to an absence of free water in N. alexis.     

Metabolic engineering of microbes for oligosaccharide and polysaccharide synthesis

Metabolic engineering has recently been embraced as an effective tool for developing whole-cell biocatalysts for oligosaccharide and polysaccharide synthesis. Microbial catalysts now provide a practical means to derive many valuable oligosaccharides, previously inaccessible through other methods, in sufficient quantities to support research and clinical applications. The synthesis process based upon these microbes is scalable as it avoids expensive starting materials. Most impressive is the high product concentrations (up to 188 g/L) achieved through microbe-catalyzed synthesis. The overall cost for selected molecules has been brought to a reasonable range (estimated $ 30–50/g).     

The AAA ATPase spastin links microtubule severing to membrane modelling

In 1999, mutations in the gene encoding the microtubule severing AAA ATPase spastin were identified as a major cause of a genetic neurodegenerative condition termed hereditary spastic paraplegia (HSP). This finding stimulated intense study of the spastin protein and over the last decade, a combination of cell biological, in vivo, in vitro and structural studies have provided important mechanistic insights into the cellular functions of the protein, as well as elucidating cell biological pathways that might be involved in axonal maintenance and degeneration. Roles for spastin have emerged in shaping the endoplasmic reticulum and the abscission stage of cytokinesis, in which spastin appears to couple membrane modelling to microtubule regulation by severing.