Impacts of the invasive alga Sargassum muticum on ecosystem functioning and food web structure

Biological invasions have the potential to cause severe alterations to the biodiversity of natural ecosystems. At the same time, variation in the diversity and composition of native communities may have an important influence on the impact of invasions. Here, effects of the invasive Japanese wireweed, Sargassum muticum, were tested across a range of native marine algal assemblages using a combined additive and substitutive design. The invasive alga significantly reduced primary production, an important component of ecosystem functioning, and increased connectance, a key property of the food webs associated with the algal resources. These impacts were mediated by changes in the proportions of intermediate and top species, as well as apparent reductions in faunal species richness and diversity. Some key alterations to faunal species composition (including the arrival of generalist species associated with S. muticum) may have been important in determining these patterns. Overall results suggest that S. muticum not only directly impeded the native algal community, but that these effects extended indirectly to the native fauna and therefore caused major changes throughout the ecosystem.     

Characterization of photodamage to escherichia coli in optical traps

Optical tweezers (infrared laser-based optical traps) have emerged as a powerful tool in molecular and cell biology. However, their usefulness has been limited, particularly in vivo, by the potential for damage to specimens resulting from the trapping laser. Relatively little is known about the origin of this phenomenon. Here we employed a wavelength-tunable optical trap in which the microscope objective transmission was fully characterized throughout the near infrared, in conjunction with a sensitive, rotating bacterial cell assay. Single cells of Escherichia coli were tethered to a glass coverslip by means of a single flagellum: such cells rotate at rates proportional to their transmembrane proton potential (. J. Mol. Biol. 138:541-561). Monitoring the rotation rates of cells subjected to laser illumination permits a rapid and quantitative measure of their metabolic state. Employing this assay, we characterized photodamage throughout the near-infrared region favored for optical trapping (790-1064 nm). The action spectrum for photodamage exhibits minima at 830 and 970 nm, and maxima at 870 and 930 nm. Damage was reduced to background levels under anaerobic conditions, implicating oxygen in the photodamage pathway. The intensity dependence for photodamage was linear, supporting a single-photon process. These findings may help guide the selection of lasers and experimental protocols best suited for optical trapping work.     

Quantitative Relationships of Five Putative Neurotransmitter Receptor Sites in Rat Hippocampal Formation

The hippocampus is well suited for studies of the interrelationships of various neurotransmitter systems in the CNS by reason of its simple laminated organization, defined connections, and variety of identified neurotransmitters. We have studied the biochemical and pharmacological properties of five radiolabeled ligand binding sites in a membrane fraction prepared from rat hippocampal formation. These binding sites are thought to identify recognition sites for neurotransmitter receptors. The rank order of ligand binding sites is [³H]muscimol > [³H]quinuclidinyl benzilate > [³Hdihydroergocryptine > [³H]dihydroalprenolol > ¹²⁵I-labeled α-bungarotoxin. All ligands have a single, saturable, high-affinity binding site. Pharmacological characterization of the ligand binding sites indicates properties consistent with the identification of these sites as neurotransmitter receptors.     

The Na+/K+ ATPase is required for septate junction function and epithelial tube-size control in the Drosophila tracheal system

Although the correct architecture of epithelial tubes is crucial for the function of organs such as the lung, kidney and vascular system, little is known about the molecular mechanisms that control tube size. We show that mutations in the ATPalpha alpha and nrv2 beta subunits of the Na+/K+ ATPase cause Drosophila tracheal tubes to have increased lengths and expanded diameters. ATPalpha and nrv2 mutations also disrupt stable formation of septate junctions, structures with some functional and molecular similarities to vertebrate tight junctions. The Nrv2 beta subunit isoforms have unique tube size and junctional functions because Nrv2, but not other Drosophila Na+/K+ ATPase beta subunits, can rescue nrv2 mutant phenotypes. Mutations in known septate junctions genes cause the same tracheal tube-size defects as ATPalpha and nrv2 mutations, indicating that septate junctions have a previously unidentified role in epithelial tube-size control. Double mutant analyses suggest that tube-size control by septate junctions is mediated by at least two discernable pathways, although the paracellular diffusion barrier function does not appear to involved because tube-size control and diffusion barrier function are genetically separable. Together, our results demonstrate that specific isoforms of the Na+/K+ ATPase play a crucial role in septate junction function and that septate junctions have multiple distinct functions that regulate paracellular transport and epithelial tube size.     

Isolation and characterization of mutants for the vesicular acetylcholine transporter gene in Drosophila melanogaster

The Drosophila vesicular acetylcholine transporter gene (Vacht) is nested within the first intron of the choline acetyltransferase gene (Cha). To isolate Vacht mutants, we performed an F(2) genetic screen and identified mutations that failed to complement Df(3R)Cha(5), a deletion lacking Cha and the surrounding genes. Of these mutations, three mapped to a small genomic region where Cha resides. Complementation tests with a Cha mutant allele and rescue experiments using a transgenic Vacht minigene have revealed that two of these three mutations are nonconditional lethal alleles of Vacht (Vacht(1) and Vacht(2) ). The other is a new temperature-sensitive allele of Cha (Cha(ts3) ). Newly isolated Vacht mutants were used to reexamine the existing Cha mutations. We found that all deficiencies uncovering Cha also lack Vacht function, reflecting the nested organization of the two genes. The effective lethal phase for Vacht(1) is the embryonic stage, whereas that for Vacht(2) is the larval stage. Viable first-instar larvae homozygous for Vacht(2) showed reduced motility. Adult flies heterozygous for Vacht mutations were found to have defective responses in the dorsal longitudinal muscles following high-frequency brain stimulation. Since cholinergic synapses have been shown to be involved in the giant fiber pathway that mediates this response, the result suggested that reduction in the Vacht activity to 50% causes an abnormality in cholinergic transmission when stressed by a high-frequency stimulus.     

Organ specificity and transcriptional control of metabolic routes revealed by expression QTL profiling of source-sink tissues in a segregating potato population

Background  

With the completion of genome sequences belonging to some of the major crop plants, new challenges arise to utilize this data for crop improvement and increased food security. The field of genetical genomics has the potential to identify genes displaying heritable differential expression associated to important phenotypic traits. Here we describe the identification of expression QTLs (eQTLs) in two different potato tissues of a segregating potato population and query the potato genome sequence to differentiate between cis- and trans-acting eQTLs in relation to gene subfunctionalization.     

Functional and intracellular localization properties of U6 promoter-expressed siRNAs, shRNAs, and chimeric VA1 shRNAs in mammalian cells

RNA polymerase III (Pol III) expression systems for short hairpin RNAs (U6 shRNAs or chimeric VA1 shRNAs) or individually expressed sense/antisense small interfering RNA (siRNA) strands have been used to trigger RNA interference (RNAi) in mammalian cells. Here we show that individually expressed siRNA expression constructs produce 21-nucleotide siRNAs that strongly accumulate as duplex siRNAs in the nucleus of human cells, exerting sequence-specific silencing activity similar to cytoplasmic siRNAs derived from U6 or VA1-expressed hairpin precursors. In contrast, 29-mer siRNAs separately expressed as sense/antisense strands fail to elicit RNAi activity, despite accumulation of these RNAs in the nucleus. Our findings delineate different intracellular accumulation patterns for the three expression strategies and suggest the possibility of a nuclear RNAi pathway that requires 21-mer duplexes.     

Malaria vectors and transmission dynamics in coastal south-western Cameroon

Background

Malaria is a major public health problem in Cameroon. Unlike in the southern forested areas where the epidemiology of malaria has been better studied prior to the implementation of control activities, little is known about the distribution and role of anophelines in malaria transmission in the coastal areas.

Methods

A 12-month longitudinal entomological survey was conducted in Tiko, Limbe and Idenau from August 2001 to July 2002. Mosquitoes captured indoors on human volunteers were identified morphologically. Species of the Anopheles gambiae complex were identified using the polymerase chain reaction (PCR). Mosquito infectivity was detected by the enzyme-linked immunosorbent assay and PCR. Malariometric indices (plasmodic index, gametocytic index, parasite species prevalence) were determined in three age groups (<5 yrs, 5–15 yrs, >15 yrs) and followed-up once every three months.

Results

In all, 2,773 malaria vectors comprising Anopheles gambiae (78.2%), Anopheles funestus (17.4%) and Anopheles nili (7.4%) were captured. Anopheles melas was not anthropophagic. Anopheles gambiae had the highest infection rates. There were 287, 160 and 149 infective bites/person/year in Tiko, Limbe and Idenau, respectively. Anopheles gambiae accounted for 72.7%, An. funestus for 23% and An. nili for 4.3% of the transmission. The prevalence of malaria parasitaemia was 41.5% in children <5 years of age, 31.5% in those 5–15 years and 10.5% in those >15 years, and Plasmodium falciparum was the predominant parasite species.

Conclusion

Malaria transmission is perennial, rainfall dependent and An. melas does not contribute to transmission. These findings are important in the planning and implementation of malaria control activities in coastal Cameroon and West Africa.

     

Immunocytochemical staining of central neurones in Periplaneta americana using monoclonal antibodies to choline acetyltransferase

Immunocytochemical mapping of cholinergic neurones in the CNS of the cockroach Periplaneta americana has been attempted using monoclonal antibodies to choline acetyltransferase (ChAT, acetyl-CoA: choline O-acetyltransferase, EC 2.3.1.6). Monoclonal antibodies 11 255 and 1E6 raised against rat brain ChAT and 1C8 raised against Drosophila melanogaster ChAT were ineffective in staining Periplaneta neurones. However, the cytoplasm of certain neuronal cell bodies was stained by monoclonal antibody 4D7 prepared against rat ChAT. Staining of cell bodies by 4D7 was enhanced following in vivo pre-treatment with colchicine. The staining of specific neurones by monoclonal antibody 4D7 indicates that these cockroach cells are rich in a protein with antigenic determinants resembling those of vertebrate ChAT. For some unidentified neurones, 4D7 staining is associated with the presence of acetylcholinesterase indicating that this monoclonal antibody offers a probe for mapping cholinergic neurones in the CNS of Periplaneta americana. The fast coxal depressor motoneurone (D(f)) was not stained by monoclonal antibody 4D7. Some neuronal processes in the sixth abdominal ganglion, and sensory cell bodies in the cerci were lightly stained by monoclonal antibody 4D7 following pre-injection of animals for 36 hr with colchicine.