Error resilience analysis of wireless image transmission using JPEG, JPEG 2000 and JPWL

The wireless extension of the JPEG 2000 standard formally known as JPWL is the newest international standard for still image compression. Different from all previous standards, this new standard was created specifically for wireless imaging applications. This paper examines the error resilience performance of the JPEG, JPEG 2000 and JPWL standards in combating multi-path and fading impairments in Rayleigh fading channels. Comprehensive objective and subjective results are presented in relation to the error resilience performance of these three standards under various conditions. The major findings in this paper reveal that a CRC approach is not a viable option for protecting wireless image data when not used in conjunction with an efficient retransmission strategy. In addition, the Reed-Solomon error correction codes in JPWL provide strong protection for wireless image transmission. However, any stronger protection beyond RS(64,32) yields diminishing returns

The Mechanism of Budding of Retroviruses from Cell Membranes

Retroviruses have evolved a mechanism for the release of particles from the cell membrane that appropriates cellular protein complexes, referred to as ESCRT-I, -II, -III, normally involved in the biogenesis of multivesicular bodies. Three different classes of late assembly (L) domains encoded in Gag, with core sequences of PPXY, PTAP, and YPXL, recruit different components of the ESCRT machinery to form a budding complex for virus release. Here, we highlight recent progress in identifying the role of different ESCRT complexes in facilitating budding, ubiquitination, and membrane targeting of avian sarcoma and leukosis virus (ASLV) and human immunodeficiency virus, type 1 (HIV-1). These findings show that retroviruses may adopt parallel budding pathways by recruiting different host factors from common cellular machinery for particle release

Cryoelectron tomography reveals periodic material at the inner side of subpellicular microtubules in apicomplexan parasites

Microtubules are dynamic cytoskeletal structures important for cell division, polarity, and motility and are therefore major targets for anticancer and antiparasite drugs. In the invasive forms of apicomplexan parasites, which are highly polarized and often motile cells, exceptionally stable subpellicular microtubules determine the shape of the parasite, and serve as tracks for vesicle transport. We used cryoelectron tomography to image cytoplasmic structures in three dimensions within intact, rapidly frozen Plasmodium sporozoites. This approach revealed microtubule walls that are extended at the luminal side by an additional 3 nm compared to microtubules of mammalian cells. Fourier analysis revealed an 8-nm longitudinal periodicity of the luminal constituent, suggesting the presence of a molecule interacting with tubulin dimers. In silico generation and analysis of microtubule models confirmed this unexpected topology. Microtubules from extracted sporozoites and Toxoplasma gondii tachyzoites showed a similar density distribution, suggesting that the putative protein is conserved among Apicomplexa and serves to stabilize microtubules

Visualising single molecules of HIV-1 and miRNA nucleic acids

BackgroundThe scarcity of certain nucleic acid species and the small size of target sequences such as miRNA, impose a significant barrier to subcellular visualization and present a major challenge to cell biologists. Here, we offer a generic and highly sensitive visualization approach (oligo fluorescent in situ hybridization, O-FISH) that can be used to detect such nucleic acids using a single-oligonucleotide probe of 19–26 nucleotides in length.ResultsWe used O-FISH to visualize miR146a in human and avian cells. Furthermore, we reveal the sensitivity of O-FISH detection by using a HIV-1 model system to show that as little as 1–2 copies of nucleic acids can be detected in a single cell. We were able to discern newly synthesized viral cDNA and, moreover, observed that certain HIV RNA sequences are only transiently available for O-FISH detection.ConclusionsTaken together, these results suggest that the O-FISH method can potentially be used for in situ probing of, as few as, 1–2 copies of nucleic acid and, additionally, to visualize small RNA such as miRNA. We further propose that the O-FISH method could be extended to understand viral function by probing newly transcribed viral intermediates; and discern the localisation of nucleic acids of interest. Additionally, interrogating the conformation and structure of a particular nucleic acid in situ might also be possible, based on the accessibility of a target sequence

The thermodynamics of Pr55Gag-RNA interaction regulate the assembly of HIV

The interactions that occur during HIV Pr55Gag oligomerization and genomic RNA packagingare essential elements that facilitate HIV assembly. However, mechanistic details ofthese interactions are not clearly defined. Here, we overcome previous limitations in producinglarge quantities of full-length recombinant Pr55Gag that is required for isothermal titrationcalorimetry (ITC) studies, and we have revealed the thermodynamic properties of HIVassembly for the first time. Thermodynamic analysis showed that the binding between RNAand HIV Pr55Gag is an energetically favourable reaction (ΔG<0) that is further enhanced bythe oligomerization of Pr55Gag. The change in enthalpy (ΔH) widens sequentially from: (1)Pr55Gag-Psi RNA binding during HIV genome selection; to (2) Pr55Gag-Guanosine Uridine(GU)-containing RNA binding in cytoplasm/plasma membrane; and then to (3) Pr55Gag-Adenosine(A)-containing RNA binding in immature HIV. These data imply the stepwiseincrements of heat being released during HIV biogenesis may help to facilitate the processof viral assembly. By mimicking the interactions between A-containing RNA and oligomericPr55Gag in immature HIV, it was noted that a p6 domain truncated Pr50Gag Δp6 is less efficientthan full-length Pr55Gag in this thermodynamic process. These data suggest a potentialunknown role of p6 in Pr55Gag-Pr55Gag oligomerization and/or Pr55Gag-RNA interaction duringHIV assembly. Our data provide direct evidence on how nucleic acid sequences and theoligomeric state of Pr55Gag regulate HIV assembly

Luminal particles within cellular microtubules.

The regulation of microtubule dynamics is attributed to microtubule-associated proteins that bind to the microtubule outer surface, but little is known about cellular components that may associate with the internal side of microtubules. We used cryoelectron tomography to investigate in a quantitative manner the three dimensional structure of microtubules in intact mammalian cells. We show that the lumen of microtubules in this native state is filled with discrete, globular particles with a diameter of 7 nm and spacings between 8 and 20 nm in neuronal cells. Cross-sectional views of microtubules confirm the presence of luminal material in vitreous sections of brain tissue. Most of the luminal particles had connections to the microtubule wall, as revealed in tomograms. A higher accumulation of particles was seen near the retracting plus ends of microtubules. The luminal particles were abundant in neurons, but were also observed in other cells, such as astrocytes and stem cells

Cryo-electron tomography of cells: connecting structure and function

Cryo-electron tomography (cryo-ET) allows the visualization of cellular structures under close-to-life conditions and at molecular resolution. While it is inherently a static approach, yielding structural information about supramolecular organization at a certain time point, it can nevertheless provide insights into function of the structures imaged, in particular, when supplemented by other approaches. Here, we review the use of experimental methods that supplement cryo-ET imaging of whole cells. These include genetic and pharmacological manipulations, as well as correlative light microscopy and cryo-ET. While these methods have mostly been used to detect and identify structures visualized in cryo-ET or to assist the search for a feature of interest, we expect that in the future they will play a more important role in the functional interpretation of cryo-tomograms

Effects of Ocean Acidification on Learning in Coral Reef Fishes

Ocean acidification has the potential to cause dramatic changes in marine ecosystems. Larval damselfish exposed to concentrations of CO2 predicted to occur in the mid- to late-century show maladaptive responses to predator cues. However, there is considerable variation both within and between species in CO2 effects, whereby some individuals are unaffected at particular CO2 concentrations while others show maladaptive responses to predator odour. Our goal was to test whether learning via chemical or visual information would be impaired by ocean acidification and ultimately, whether learning can mitigate the effects of ocean acidification by restoring the appropriate responses of prey to predators. Using two highly efficient and widespread mechanisms for predator learning, we compared the behaviour of pre-settlement damselfish Pomacentrus amboinensis that were exposed to 440 µatm CO2 (current day levels) or 850 µatm CO2, a concentration predicted to occur in the ocean before the end of this century. We found that, regardless of the method of learning, damselfish exposed to elevated CO2 failed to learn to respond appropriately to a common predator, the dottyback, Pseudochromis fuscus. To determine whether the lack of response was due to a failure in learning or rather a short-term shift in trade-offs preventing the fish from displaying overt antipredator responses, we conditioned 440 or 700 µatm-CO2 fish to learn to recognize a dottyback as a predator using injured conspecific cues, as in Experiment 1. When tested one day post-conditioning, CO2 exposed fish failed to respond to predator odour. When tested 5 days post-conditioning, CO2 exposed fish still failed to show an antipredator response to the dottyback odour, despite the fact that both control and CO2-treated fish responded to a general risk cue (injured conspecific cues). These results indicate that exposure to CO2 may alter the cognitive ability of juvenile fish and render learning ineffective