Explore the vast range of titles available.

ATP-binding cassette transporters are ubiquitous membrane protein complexes that move substrates across membranes. They do so using ATP-induced conformational changes in their nucleotide-binding domains to alter the conformation of the transport cavity formed by their transmembrane domains. In Escherichia coli, an ATP-binding cassette transporter-like complex composed of FtsE (nucleotide-binding domain) and FtsX (transmembrane domain) has long been known to be important for cytokinesis, but its role in the process has remained mysterious. Here we identify FtsEX as a regulator of cell-wall hydrolysis at the division site. Cell-wall material synthesized by the division machinery is shared initially by daughter cells and must be split by hydrolytic enzymes called \"amidases\" to drive daughter-cell separation. We recently showed that the amidases require activation at the cytokinetic ring by proteins with LytM domains, of which EnvC is the most critical. In this report, we demonstrate that FtsEX directly recruits EnvC to the septum via an interaction between EnvC and a periplasmic loop of FtsX. Importantly, we also show that FtsEX variants predicted to be ATPase defective still recruit EnvC to the septum but fail to promote cell separation. Our results thus suggest that amidase activation via EnvC in the periplasm is regulated by conformational changes in the FtsEX complex mediated by ATP hydrolysis in the cytoplasm. Since FtsE has been reported to interact with the tubulin-like FtsZ protein, our model provides a potential mechanism for coupling amidase activity with the contraction of the FtsZ cytoskeletal ring.

The model brown alga Ectocarpus has a haploid-diploid life cycle, involving alternation between two independent multicellular generations, the gametophyte and the sporophyte. Recent work has shown that alternation of generations is not determined by ploidy but is rather under genetic control, involving at least one master regulatory locus, OUROBOROS (ORO). Using cell biology approaches combined with measurements of generation-specific transcript abundance we provide evidence that alternation of generations can also be regulated by non-cell autonomous mechanisms. The Ectocarpus sporophyte produces a diffusible factor that causes major developmental reprogramming in gametophyte cells. Cells become resistant to reprogramming when the cell wall is synthetized, suggesting that the cell wall may play a role in locking an individual into the developmental program that has been engaged. A functional ORO gene is necessary for the induction of the developmental switch. Our results highlight the role of the cell wall in maintaining the differentiated generation stage once the appropriate developmental program has been engaged and also indicate that ORO is a key member of the developmental pathway triggered by the sporophyte factor. Alternation between gametophyte and sporophyte generations in Ectocarpus is surprisingly labile, perhaps reflecting an adaptation to the variable seashore environment inhabited by this alga.

The ejection of material from Mars is thought to be caused by large impacts that would heat much of the ejecta to high temperatures. Images of the magnetic field of martian meteorite ALH84001 reveal a spatially heterogeneous pattern of magnetization associated with fractures and rock fragments. Heating the meteorite to 40°C reduces the intensity of some magnetic features, indicating that the interior of the rock has not been above this temperature since before its ejection from the surface of Mars. Because this temperature cannot sterilize most bacteria or eukarya, these data support the hypothesis that meteorites could transfer life between planets in the solar system.

Microtubules function in concert with associated proteins that modify microtubule behavior and/or transmit signals that effect changes in growth. To better understand how microtubules and their associated proteins influence growth, we analyzed one family of microtubule-associated proteins, the END BINDING1 (EB1) proteins, in Arabidopsis thaliana (EB1a, EB1b, and EB1c). We find that antibodies directed against EB1 proteins colocalize with microtubules in roots, an observation that confirms previous reports using EB1-GFP fusions. We also find that T-DNA insertion mutants with reduced expression from EB1 genes have roots that deviate toward the left on vertical or inclined plates. Mutant roots also exhibit extended horizontal growth before they bend downward after tracking around an obstacle or after a 90° clockwise reorientation of the root. These observations suggest that leftward deviations in root growth may be the result of delayed responses to touch and/or gravity signals. Root lengths and widths are normal, indicating that the delay in bend formation is not due to changes in the overall rate of growth. In addition, the genotype with the most severe defects responds to low doses of microtubule inhibitors in a manner indistinguishable from the wild type, indicating that microtubule integrity is not a major contributor to the leftward deviations in mutant root growth.

Background Kinesin-5 (Eg-5) motor proteins are essential for maintenance of spindle bipolarity in animals. The roles of Kinesin-5 proteins in other systems, such as Arabidopsis, Dictyostelium, and sea urchin are more varied. We are studying Kinesin-5-like proteins during early development in the brown alga Silvetia compressa . Previously, this motor was shown to be needed to assemble a bipolar spindle, similar to animals. This report builds on those findings by investigating the localization of the motor and probing its function in spindle maintenance. Findings Anti-Eg5 antibodies were used to investigate localization of Kinesin-5-like proteins in brown algal zygotes. In interphase zygotes, localization was predominantly within the nucleus. As zygotes entered mitosis, these motor proteins strongly associated with spindle poles and, to a lesser degree, with the polar microtubule arrays and the spindle midzone. In order to address whether Kinesin-5-like proteins are required to maintain spindle bipolarity, we applied monastrol to synchronized zygotes containing bipolar spindles. Monastrol is a cell-permeable chemical inhibitor of the Kinesin-5 class of molecular motors. We found that inhibition of motor function in pre-formed spindles induced the formation of multipolar spindles and short bipolar spindles. Conclusion Based upon these localization and inhibitor studies, we conclude that Kinesin-5-like motors in brown algae are more similar to the motors of animals than those of plants or protists. However, Kinesin-5-like proteins in S. compressa serve novel roles in spindle formation and maintenance not observed in animals.

Many zygotes and spores of brown algae are photosensitive and establish a developmental axis in accordance with directional light cues. Ectocarpus siliculosus is being advanced as a genetic and genomic model organism for investigating brown alga development, and this report investigates photopolarization of the growth axis of mitospores. When exposed to unidirectional light, mitospores photopolarized and established a growth axis such that germination was preferentially localized to the shaded hemisphere of the spore body. The roles of the microtubule cytoskeleton and endomembrane cycling in the photopolarization process were investigated using pharmacological agents. Disruption of microtubule dynamics progressively reduced the percentage of mitospores that photopolarized, while inhibition of vesicle secretion blocked photopolarization nearly completely. Chronic treatment with these pharmacological agents severely affected algal morphogenesis. Microtubules in mitospores and algal filaments were imaged by confocal microscopy. Mitospores contained a radial microtubule array, emanating from a centrosome associated with the nuclear envelope. At germination, the radial array gradually transitioned into a longitudinal array with microtubules extending into the emerging apex. At mitosis, spindles were aligned with the growth axis of cylindrical cells in the filament, and the division plane bisected the spindle axis. These studies demonstrate that dynamic membrane cycling and microtubule assembly play fundamental roles in photopolarization and provide a foundation for future genetic and genomic investigations of this important developmental process.

We have previously described an example of extensively A-to-G edited cDNA derived from adult heads of the fruitfly Drosophila melanogaster . In that study, the source of the predicted antisense RNA pairing strand for template recognition by dADAR editase was not identified, and the biological significance of the observed hyperediting was not known. Here, each of these questions is addressed. 4f-rnp and CG4202 are closely adjacent X-linked genes located on opposite DNA strands which produce convergent transcripts. Developmentally regulated antisense CG4202 readthrough mRNA is shown to arise by activation of an upstream promoter P2 during the late embryo stage of fly development. The CG4202 readthrough transcripts pair with 4f-rnp mRNA to form double-stranded molecules, as indicated by A-to-G editing observed in both RNA strands. It would be predicted that perfect RNA duplexes would be targeted for modification/degradation by enzyme pathways which recognize double-stranded RNAs, leading to decline in 4f-rnp mRNA levels, and this is what is observed. It would also be predicted that, if 4f-rnp/CG4202 mRNAs form near perfect duplex regions for protein recognition, the CG4202 readthrough region would be highly evolutionarily conserved, and this is what is found. The observation using quantitative RT-PCR that CG4202 readthrough and 4f-rnp transcript levels are inversely related suggests a role for the antisense RNA in posttranscriptional regulation of 4f-rnp gene expression during development. Potential molecular mechanisms which could lead to this result are discussed, one of which is targeted transcript degradation via the RNAi pathway. Insofar as the dADAR editase and RNAi pathways are known to be constitutive in this system, it is likely that control of antisense RNA transcription is the rate-limiting factor. The results provide insight into potential roles of naturally occurring antisense RNAs in regulation of eukaryotic gene expression.

The long-term security of geological CO2 storage hinges on the integrity of caprock formations, traditionally considered vulnerable to acid-induced dissolution from injected CO2 and associated impurities. Contrary to this view, we demonstrate that impurity-bearing CO2 can enhance caprock integrity through mineralization-driven self-sealing. Reactive transport modeling across three CO2 storage sites shows that silicate minerals, particularly smectite and chlorite, facilitate the precipitation of sealing carbonates such as ankerite and magnesite. These pore-filling reactions are sustained by divalent cations released from calcium-, iron-, and magnesium-rich aluminosilicates, progressively reducing pore connectivity and CO2 diffusivity. We show that, over a 100-year period, CO2 diffusion in reactive caprocks decreases by approximately 0.8–1 order of magnitude. We propose an empirical relationship describing the time-dependent decline in diffusion. As these mineral assemblages are common in seal rocks globally, the identified self-sealing mechanisms significantly lower leakage risk and provide a broadly applicable pathway for improving long-term CO2 containment. This work reframes impurity-bearing CO2 not as a threat, but as a catalyst for subsurface resilience, opening new avenues for designing safer and more adaptive carbon storage systems.

This study pools published data to describe the increase in glomerular filtration rate (GFR) from very premature neonates to young adults. The data comprises measured GFR (using polyfructose, 51 Cr-EDTA, mannitol or iohexol) from eight studies ( n  = 923) and involved very premature neonates (22 weeks postmenstrual age) to adulthood (31 years). A nonlinear mixed effects approach (NONMEM) was used to examine the influences of size and maturation on renal function. Size was the primary covariate, and GFR was standardized for a body weight of 70 kg using an allometric power model. Postmenstrual age (PMA) was a better descriptor of maturational changes than postnatal age (PNA). A sigmoid hyperbolic model described the nonlinear relationship between GFR maturation and PMA. Assuming an allometric coefficient of 3/4, the fully mature (adult) GFR is predicted to be 121.2 mL/min per 70 kg [95% confidence interval (CI) 117–125]. Half of the adult value is reached at 47.7 post-menstrual weeks (95%CI 45.1–50.5), with a Hill coefficient of 3.40 (95%CI 3.03–3.80). At 1-year postnatal age, the GFR is predicted to be 90% of the adult GFR. Glomerular filtration rate can be predicted with a consistent relationship from early prematurity to adulthood. We propose that this offers a clinically useful definition of renal function in children and young adults that is independent of the predictable changes associated with age and size.