Auxin transport promotes Arabidopsis lateral root initiation

Lateral root development in Arabidopsis provides a model for the study of hormonal signals that regulate postembryonic organogenesis in higher plants. Lateral roots originate from pairs of pericycle cells, in several cell files positioned opposite the xylem pole, that initiate a series of asymmetric, transverse divisions. The auxin transport inhibitor N-1-naphthylphthalamic acid (NPA) arrests lateral root development by blocking the first transverse division(s). We investigated the basis of NPA action by using a cell-specific reporter to demonstrate that xylem pole pericycle cells retain their identity in the presence of the auxin transport inhibitor. However, NPA causes indoleacetic acid (IAA) to accumulate in the root apex while reducing levels in basal tissues critical for lateral root initiation. This pattern of IAA redistribution is consistent with NPA blocking basipetal IAA movement from the root tip. Characterization of lateral root development in the shoot meristemless1 mutant demonstrates that root basipetal and leaf acropetal auxin transport activities are required during the initiation and emergence phases, respectively, of lateral root development.     

The domain-swapped dimer of cyanovirin-N contains two sets of oligosaccharide binding sites in solution

The binding of high-mannose oligosaccharides to the domain-swapped dimeric form of the potent HIV-inactivating protein cyanovirin-N (CV-N) was investigated in solution by NMR, complementing recent structural studies by X-ray crystallography on similar complexes [J. Biol. Chem. 277 (2002) 34336]. The crystal structures of CV-N dimer complexed with Man-9 and hexamannoside revealed two carbohydrate binding sites on opposite ends of the molecule. No binding was observed at site 1, previously identified on the solution monomer of CV-N [Structure 9 (2001) 931; Shenoy et al., Chem. Biol. 9 (2002) 1109]. Here, we report the presence of four sugar binding sites on the CV-N dimer in solution, identified by chemical shift mapping with hexamannoside and nonamannoside, synthetic substructures of Man-9. Our results demonstrate that in solution the domain-swapped CV-N dimer, like the CV-N monomer, contains two types of sites that are available for carbohydrate binding, suggesting that the occlusion of the primary sites in the crystal is due to specific features of the solid state.     

Polyamine transport system mediates agmatine transport in mammalian cells

Agmatine is a biogenic amine with the capacity toregulate a number of nonreceptor-mediated functions in mammalian cells, including intracellular polyamine content and nitric oxide generation. We observed avid incorporation of agmatine into several mammalian celllines and herein characterize agmatine transport in mammalian cells. Intransformed NIH/3T3 cells, agmatine uptake is energy dependent with asaturable component indicative of carrier-mediated transport. Transportdisplays an apparent Michaelis-Menten constant of 2.5 µM and amaximal velocity of 280 pmol · min¹ · mg¹ proteinand requires a membrane potential across the plasma membrane foruptake. Competition with polyamines, but not cationic molecules thatutilize the y⁺ system transporter, suppresses agmatineuptake. Altering polyamine transporter activity results in parallelchanges in polyamine and agmatine uptake. Furthermore, agmatine uptakeis abrogated in a polyamine transport-deficient human carcinoma cellline. These lines of evidence demonstrate that agmatine utilizes, and is dependent on, the polyamine transporter for cellular uptake. Thefact that this transport system is associated with proliferation couldbe of consequence to the antiproliferative effects of agmatine.

     

Genetic Evidence for Multiple Sources of the Non-Native Fish Cichlasoma urophthalmus (Günther; Mayan Cichlids) in Southern Florida

The number and diversity of source populations may influence the genetic diversity of newly introduced populations and affect the likelihood of their establishment and spread. We used the cytochrome b mitochondrial gene and nuclear microsatellite loci to identify the sources of a successful invader in southern Florida, USA, Cichlasoma urophthalmus (Mayan cichlid). Our cytochrome b data supported an introduction from Guatemala, while our microsatellite data suggested movement of Mayan Cichlids from the upper Yucatán Peninsula to Guatemala and introductions from Guatemala and Belize to Florida. The mismatch between mitochondrial and nuclear genomes suggests admixture of a female lineage from Guatemala, where all individuals were fixed for the mitochondrial haplotype found in the introduced population, and a more diverse but also relatively small number of individuals from Belize. The Florida cytochrome b haplotype appears to be absent from Belize (0 out of 136 fish screened from Belize had this haplotype). Genetic structure within the Florida population was minimal, indicating a panmictic population, while Mexican and Central American samples displayed more genetic subdivision. Individuals from the Upper Yucatán Peninsula and the Petén region of Guatemala were more genetically similar to each other than to fish from nearby sites and movement of Mayan Cichlids between these regions occurred thousands of generations ago, suggestive of pre-Columbian human transportation of Mayan Cichlids through this region. Mayan Cichlids present a rare example of cytonuclear disequilibrium and reduced genetic diversity in the introduced population that persists more than 30 years (at least 7–8 generations) after introduction. We suggest that hybridization occurred in ornamental fish farms in Florida and may contribute their establishment in the novel habitat. Hybridization prior to release may contribute to other successful invasions.     

Defects in mitochondrial fatty acid synthesis result in failure of multiple aspects of mitochondrial biogenesis in Saccharomyces cerevisiae

Mitochondrial fatty acid synthesis (mtFAS) shares acetyl‐CoA with the Krebs cycle as a common substrate and is required for the production of octanoic acid (C8) precursors of lipoic acid (LA) in mitochondria. MtFAS is a conserved pathway essential for respiration. In a genetic screen in Saccharomyces cerevisiae designed to further elucidate the physiological role of mtFAS, we isolated mutants with defects in mitochondrial post‐translational gene expression processes, indicating a novel link to mitochondrial gene expression and respiratory chain biogenesis. In our ensuing analysis, we show that mtFAS, but not lipoylation per se, is required for respiratory competence. We demonstrate that mtFAS is required for mRNA splicing, mitochondrial translation and respiratory complex assembly, and provide evidence that not LA per se, but fatty acids longer than C8 play a role in these processes. We also show that mtFAS‐ and LA‐deficient strains suffer from a mild haem deficiency that may contribute to the respiratory complex assembly defect. Based on our data and previously published information, we propose a model implicating mtFAS as a sensor for mitochondrial acetyl‐CoA availability and a co‐ordinator of nuclear and mitochondrial gene expression by adapting the mitochondrial compartment to changes in the metabolic status of the cell.     

How formalin affects the outcome of routine and special stains

The discovery of formaldehyde for preserving tissue structures produced a new dimension in microscopy. Preserving structure and morphology became important; therefore, identifying a proper fixing agent for particular structures, chemical entities, and tissues, also became important. The methods for demonstrating tissue structures evolved and were implemented with careful observation and documentation of the results and outcomes. Formalin was incorporated into many techniques, and provided helpful results in many cases and hindrances in others. The effects of formalin on the outcomes of routine and special staining techniques are reported here.     

Community structure of lice (Insecta: Phthiraptera) from two sympatric gull species: kelp gull (Larus dominicanus) and Franklin's gull (Larus pipixcan) in Talcahuano, Chile

A total of 1,177 lice of four species were collected from 124 kelp gulls (Larus dominicanus) and 137 lice of the same four species from 60 Franklin's gulls (Larus pipixcan). The louse Saemundssonia lari (O Fabricius) (Phthiraptera: Philopteridae) was the most numerous on both gull species, with infestation rates of 4.9 on kelp gulls and 1.8 on Franklin's gulls. The second most abundant louse was Quadraceps punctatus (Burmeister), with a high infestation rate but low prevalence on kelp gulls; those parameters were much lower among lice from Franklin's gulls. The composition and community structure of the lice were similar on both host species, but not their infestation rates. In addition, the feather mite Zachvatkinia larica Mironov (Acari: Avenzoariidae) is recorded from kelp gulls and Franklin's gulls for the first time, while the gamasid mite Larinyssus sp. is recorded from kelp gulls, also for the first time. The population parameters of all species of ectoparasites are discussed.     

Regulation of yeast chronological life span by TORC1 via adaptive mitochondrial ROS signaling

Here we show that yeast strains with reduced target of rapamycin (TOR) signaling have greater overall mitochondrial electron transport chain activity during growth that is efficiently coupled to ATP production. This metabolic alteration increases mitochondrial membrane potential and reactive oxygen species (ROS) production, which we propose supplies an adaptive signal during growth that extends chronological life span (CLS). In strong support of this concept, uncoupling respiration during growth or increasing expression of mitochondrial manganese superoxide dismutase significantly curtails CLS extension in tor1Δ strains, and treatment of wild-type strains with either rapamycin (to inhibit TORC1) or menadione (to generate mitochondrial ROS) during growth is sufficient to extend CLS. Finally, extension of CLS by reduced TORC1/Sch9p-mitochondrial signaling occurs independently of Rim15p and is not a function of changes in media acidification/composition. Considering the conservation of TOR-pathway effects on life span, mitochondrial ROS signaling may be an important mechanism of longevity regulation in higher organisms.