Differential Use of Trails by Forest Mammals and the Implications for Camera-Trap Studies: A Case Study from Belize

Relative abundance indices are often used to compare species abundance between sites. The indices assume that species have similar detection probabilities, or that differences between detection probabilities are known and can be corrected for. Indices often consist of encounter frequencies of footprints, burrows, markings or photo captures along trails or transect lines, but the assumption of equal detection probabilities is rarely validated. This study analyzes detection probabilities of a range of Neotropical mammals on trails in dense secondary forests, using camera-trap and track data. Photo captures of the two large cats, jaguars ( Panthera onca ) and pumas ( Puma concolor ), were correlated solely with trail variables, while photo captures of their potential prey species had no correlation or negative correlation with trail variables. The Neotropical mammals varied greatly in their tendency to follow or cross trails based on footprints surveys. This indicates that camera locations on trails will have varying detection probability for these Neotropical mammals. Even the two similar-sized jaguars and pumas, occupying relatively similar niches, differed subtly in their use of trails. Pumas followed trails more completely while jaguars were more likely to deviate from trails. The ecological significance of these findings is that jaguars seem to be more willing to use the forest matrix away from trails than do pumas. We conclude that trail-based indices, such as photographic captures or tracks along trails, are not appropriate for comparison between Neotropical species, and not even between relatively similar species like jaguars and pumas.     

Understanding signal integration through targeted mutations of an adapter protein

Immunoreceptor engagement leads to the activation of multiple second messenger cascades, and integration of these pathways requires proper function of a number of adapter proteins. Although adapters possess no intrinsic enzymatic function, they nucleate the formation of multi-molecular protein complexes to support downstream signaling. Since adapters contain functionally distinct domains, intense investigation has been devoted to understanding how these regions act to integrate signals. This review describes the evolution of studies investigating one of these adapters, the SH2 domain-containing leukocyte protein of 76 kDa. Through utilizing biochemical, genetic and imaging techniques, a model has emerged describing how this adapter regulates signals resulting in complex immune responses.     

A single amino acid in human APOBEC3F alters susceptibility to HIV-1 Vif

Human APOBEC3F (huA3F) potently restricts the infectivity of HIV-1 in the absence of the viral accessory protein virion infectivity factor (Vif). Vif functions to preserve viral infectivity by triggering the degradation of huA3F but not rhesus macaque A3F (rhA3F). Here, we use a combination of deletions, chimeras, and systematic mutagenesis between huA3F and rhA3F to identify Glu(324) as a critical determinant of huA3F susceptibility to HIV-1 Vif-mediated degradation. A structural model of the C-terminal deaminase domain of huA3F indicates that Glu(324) is a surface residue within the α4 helix adjacent to residues corresponding to other known Vif susceptibility determinants in APOBEC3G and APOBEC3H. This structural clustering suggests that Vif may bind a conserved surface present in multiple APOBEC3 proteins.     

Cys Palmitoylation of the β Subunit Modulates Gating of the Epithelial Sodium Channel

The epithelial Na⁺ channel (ENaC) is comprised of three homologous subunits (α, β, and γ) that have a similar topology with two transmembrane domains, a large extracellular region, and cytoplasmic N and C termini. Although ENaC activity is regulated by a number of factors, palmitoylation of its cytoplasmic Cys residues has not been previously described. Fatty acid-exchange chemistry was used to determine whether channel subunits were Cys-palmitoylated. We observed that only the β and γ subunits were modified by Cys palmitoylation. Analyses of ENaCs with mutant β subunits revealed that Cys-43 and Cys-557 were palmitoylated. Xenopus oocytes expressing ENaC with a β C43A,C557A mutant had significantly reduced amiloride-sensitive whole cell currents, enhanced Na⁺ self-inhibition, and reduced single channel P_o when compared with wild-type ENaC, while membrane trafficking and levels of surface expression were unchanged. Computer modeling of cytoplasmic domains indicated that β Cys-43 is in proximity to the first transmembrane α helix, whereas β Cys-557 is within an amphipathic α-helix contiguous with the second transmembrane domain. We propose that β subunit palmitoylation modulates channel gating by facilitating interactions between cytoplasmic domains and the plasma membrane.     

Site fidelity and homing in tropical coral reef cardinalfish: are they using olfactory cues?

A number of tropical coral reef fish hold station and display restricted home ranges. If artificially displaced, they will return to their home site. We questioned if marine fish are using the same mechanisms for home site detection as many freshwater fish, that is, by olfactory sensing of chemical signals deposited on the substrate by conspecific fish. Behavioral experiments were conducted on Lizard Island Research Station, Queensland, Australia, in 2001 and 2002. Five-lined cardinalfish (Cheilodipterus quinquelineatus) were tested in groups with split-branded cardinalfish (Apogon compressus) as a reference species and individually against Apogon leptacanthus as well as conspecifics of another reef site. The group tests showed that both species preferred artificial reef sites that had previously been occupied by conspecifics. Individual C. quinquelineatus preferred scent of conspecifics from their own reef site to that from another site. They also preferred the scent released by artificial reefs previously occupied by conspecifics of their reef site to that of similar reefs previously occupied by conspecifics of another reef site. No discrimination between species from the same reef site was obtained in experiments with individual fish. Our data suggest that cardinalfish are keeping station and are homing by use of conspecific olfactory signals.     

gamma-synuclein has a dynamic intracellular localization

gamma-Synuclein is a member of the synuclein family consisting of three proteins. Within the last several years increasing attention has focused on these proteins because of their role in human diseases. alpha-Synuclein relevance to Parkinson's disease is based on mutations found in familial cases of the disease and its presence in filaments and inclusion bodies in sporadic cases. gamma-Synuclein is implicated in some forms of cancer and ocular diseases, while beta-synuclein may antagonize their pathological functions. In this paper we present data on the localization and properties of gamma-synuclein in several neuronal and nonneuronal cell cultures. We show that contrary to the current opinion, gamma-synuclein is not an exclusively cytoplasmic protein, but has a dynamic localization and can associate with subcellular structures. It is present in the perinuclear area and may be associated to centrosomes. On late steps of mitosis gamma-synuclein is not found in the centrosomes, and redistributes to the midbody in telophase. Under stress conditions a translocation of gamma-synuclein from the perinuclear area to the nucleus occurs exhibiting nucleocytoplasmic shuttling. gamma-Synuclein overexpression reduces neurite outgrowth in a greater extent then alpha-synuclein overexpression. These data support the view that gamma-synuclein may change its intracellular localization and associate with subcellular structures in response to intracellular signaling or stress.