Phenotypic heterogeneity in the stargazin allelic series

The stargazer mutant mouse is characterized by its ataxic gait, head tossing, and absence seizures. The mutation was identified in the gamma2 subunit gene of the high voltage-dependent calcium channel, Cacng2. Subsequently, two allelic variants of stargazer have arisen, waggler and stargazer 3J. In this study, we have compared these new alleles to the original stargazer allele. All three mutations affect the Cacng2 mRNA levels as they all arise from disruptions within the introns of this gene. Our results show that the mutations cause reduced Cacng2 mRNA and protein levels. Stargazer and waggler mice have the least amount of mRNA and undetectable protein, whereas stargazer 3J appears to be the mildest allele, both in terms of the phenotype and protein expression. Electroencephalographic (EEG) analysis confirmed that stargazer has frequent spike-wave discharges (SWDs); the average duration of each discharge burst is 5 seconds and recurs every minute. The waggler allele causes a greater variation in SWD activity depending on the individual mouse, and the stargazer 3J mouse has no SWDs. The preliminary characterization of this heterogeneous allelic series provides a basis to explore more biochemical and physiological parameters relating to the role of the Cacng2 product in calcium channel activity, AMPA receptor localization, and cerebellar disturbances.     

The U5 snRNA internal loop 1 is a platform for Brr2, Snu114 and Prp8 protein binding during U5 snRNP assembly

The U5 small nuclear ribonucleoprotein particle (snRNP) forms the heart of the spliceosome which is required for intron removal from pre‐mRNA. The proteins Prp8, Snu114 and Brr2 all assemble with the U5 small nuclear RNA (snRNA) to produce the U5 snRNP. Successful assembly of the U5 snRNP, then incorporation of this snRNP into the U4/U6.U5 tri‐snRNP and the spliceosome, is essential for producing an active spliceosome. We have investigated the requirements for Prp8, Snu114 and Brr2 association with the U5 snRNA to form the U5 snRNP in yeast. Mutations were constructed in the highly conserved loop 1 and internal loop 1 (IL1) of the U5 snRNA and their function assessed in vivo. The influence of these U5 mutations on association of Prp8, Snu114 and Brr2 with the U5 snRNA were then determined. U5 snRNA loop 1 and both sides of IL1 in U5 were important for association of Prp8, Snu114 and Brr2 with the U5 snRNA. Mutations in the 3′ side of U5 IL1 resulted in the greatest reduction of Prp8, Snu114 and Brr2 association with the U5 snRNA. Genetic screening of brr2 and U5 snRNA mutants revealed synthetic lethal interactions between alleles in Brr2 and the 3′ side of U5 snRNA IL1 which reflects reduced association between Brr2 and U5 IL1. We propose that the U5 snRNA IL1 is a platform for protein binding and is required for Prp8, Brr2 and Snu114 association with the U5 snRNA to form the U5 snRNP. J. Cell. Biochem. 114: 2770–2784, 2013. © 2013 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals Inc.     

Spatial Variation in the Population Structure and Reproductive Biology of Rimicaris hybisae (Caridea: Alvinocarididae) at Hydrothermal Vents on the Mid-Cayman Spreading Centre

The dynamics and microdistribution of faunal assemblages at hydrothermal vents often reflect the fine-scale spatial and temporal heterogeneity of the vent environment. This study examined the reproductive development and population structure of the caridean shrimp Rimicaris hybisae at the Beebe and Von Damm Vent Fields (Mid-Cayman Spreading Centre, Caribbean) using spatially discrete samples collected in January 2012. Rimicaris hybisae is gonochoric and exhibits iteroparous reproduction. Oocyte size-frequency distributions (21-823 µm feret diameters) varied significantly among samples. Embryo development was asynchronous among females, which may result in asynchronous larval release for the populations. Specimens of R. hybisae from the Von Damm Vent Field (2294 m) were significantly larger than specimens from the Beebe Vent Field. Brooding females at Von Damm exhibited greater size-specific fecundity, possibly as a consequence of a non-linear relationship between fecundity and body size that was consistent across both vent fields. Samples collected from several locations at the Beebe Vent Field (4944–4972 m) revealed spatial variability in the sex ratios, population structure, size, and development of oocytes and embryos of this mobile species. Samples from the Von Damm Vent Field and sample J2-613-24 from Beebe Woods exhibited the highest frequencies of ovigerous females and significantly female-biased sex ratios. Environmental variables within shrimp aggregations may influence the distribution of ovigerous females, resulting in a spatially heterogeneous pattern of reproductive development in R. hybisae, as found in other vent taxa.     

Viral phenotypes and antibody responses in long-term survivors infected with attenuated human immunodeficiency virus type 1 containing deletions in the nef and long terminal repeat regions

The Sydney Blood Bank Cohort (SBBC) consists of eight blood transfusion recipients infected with nef-attenuated human immunodeficiency virus type 1 (HIV-1) acquired from a single donor. Here, we show that viral phenotypes and antibody responses differ considerably between individual cohort members, despite the single source of infection. Replication of isolated virus varied from barely detectable to similar to that of the wild-type virus, and virus isolated from five SBBC members showed coreceptor usage signatures unique to each individual. Higher viral loads and stronger neutralizing antibody responses were associated with better-replicating viral strains, and detectable viral replication was essential for the development of strong and sustained humoral immune responses. Despite the presence of strong neutralizing antibodies in a number of SBBC members, disease progression was not prevented, and each cohort member studied displayed a unique outcome of infection with nef-attenuated HIV-1.     

Current understanding of <Emphasis Type="Italic">Phaeocystis</Emphasis> ecology and biogeochemistry,and perspectives for future research

The phytoplankton genus Phaeocystis has well-documented, spatially and temporally extensive blooms of gelatinous colonies; these are associated with release of copious amounts of dimethyl sulphide (an important climate-cooling aerosol) and alterations of material flows among trophic levels and export from the upper ocean. A potentially salient property of the importance of Phaeocystis in the marine ecosystem is its physiological capability to transform between solitary cell and gelatinous colonial life cycle stages, a process that changes organism biovolume by 6–9 orders of magnitude, and which appears to be activated or stimulated under certain circumstances by chemical communication. Both life-cycle stages can exhibit rapid, phased ultradian growth. The colony skin apparently confers protection against, or at least reduces losses to, smaller zooplankton grazers and perhaps viruses. There are indications that Phaeocystis utilizes chemistry and/or changes in size as defenses against predation, and its ability to create refuges from biological attack is known to stabilize predator–prey dynamics in model systems. Thus the life cycle form in which it occurs, and particularly associated interactions with viruses, determines whether Phaeocystis production flows through the traditional “great fisheries” food chain, the more regenerative microbial food web, or is exported from the mixed layer of the ocean.Despite this plethora of information regarding the physiological ecology of Phaeocystis, fundamental interactions between life history traits and system ecology are poorly understood. Research summarized here, and described in the various papers in this special issue, derives from a central question: how do physical (light, temperature, particle distributions, hydrodynamics), chemical (nutrient resources, infochemistry, allelopathy), biological (grazers, viruses, bacteria, other phytoplankton), and self-organizational mechanisms (stability, indirect effects) interact with life-cycle transformations of Phaeocystis to mediate ecosystem patterns of trophic structure, biodiversity, and biogeochemical fluxes? Ultimately the goal is to understand and thus predict why Phaeocystis occurs when and where it does, and the bio-feedbacks between this keystone species and the multitrophic level ecosystem.     

Ecological investigations of blooms of colonial Phaeocystis pouchetti--I. Abundance, biochemical composition, and metabolic rates

A winter bloom of the colonial stage of the prymnesiophyte Phaeocystispouchetit was studied in the 13-m³ mesocosms of the Marine EcosystemResearch Laboratory on Narragansett Bay, Rhode Island The tankswere temperature regulated at 4±2°C but differedin their nutrient concentrations and in situ irradiances. Oneof the tanks was a control without added nutrients, one receiveda temporary nutrient spike and two others received daily N/P/Siinputs. Photosynthesis and growth rates of colonies exposedto a range of natural light levels were measured at weekly intervals.Particulate carbon production and release of dissolved organiccarbon (DOC) by the entire plankton community was determinedconcurrently. Photosynthesis and growth rates of Phaeocystisin tanks receiving daily nutrient additions were asymptoticfunctions of irradiance. Light-saturated rates exhibited asymptoticrelationships with dissolved inorganic nitrogen (N) levels.N-Limited populations showed more variable responses. Althoughirradiance and N availability regulated the population dynamicsof Phaeocystis, the presence or absence of silicate (S₁) influencedits relative importance in each tank. Phaeocystis dominatedcommunity metabolism in the absence of Si, but co-occurred withextensive stands of diatoms when Si was available. A significantpositive correlation was found between the contribution by Phaeocystisto community production and the proportion of photosynthatereleased as DOC In all tanks, Phaeocystis populations exhibitedcycles of abundance in which division of cells within coloniespreceded the multiplication of colonies. The production of newcolonies apparently occurred via two mechanisms: the formationof colonies from solitary cells, and the cleavage of largercolonies into smaller daughter colonies. Phaeocystis in tankswith near undetectable nutrient levels contained C:N, C:Chla, and C:ATP ratios several times higher than colonies in nutnent-repletetanks. Phaeocystis C:Chl a and C:ATP ratios were substantiallygreater than those of non-gelatinous phytoplankton due to carbohydratestorage in colony gelatin In contrast, C:N ratios in Phaeocystisand non-gelatinous phytoplankton were similar, suggesting astorage depot of organic N outside of the cells. The resultssupport the notion that Phaeocystis colonies function as biologicalentities rather than as passive aggregations of cells.     

The assembly of a highly ordered component of the cell wall: The role of heritable factors and of physical structure

Summary An analysis has been made of the biogenesis of the highly ordered lattice structure which comprises an integral part of the cell wall of Chlamydomonas reinhardi. By examining mutants showing various wall defects, it has been shown that in some mutants lattice assembly will only occur in the presence of a particular kind of physical structure; in others the composition of the medium influences assembly. The role of a heritable factor in lattice assembly has also been demonstrated; after prolonged vegetative culture certain mutants lose the ability to form lattice, but regain this ability on passing through the diploid sexual phase. An attempt is made to integrate this information to provide a model for the control of assembly and inheritance of the wall.