Making decisions with the future in mind: Developmental and comparative identification of mental time travel

Mechanisms that produce behavior which increase future survival chances provide an adaptive advantage. The flexibility of human behavior is at least partly the result of one such mechanism, our ability to travel mentally in time and entertain potential future scenarios. We can study mental time travel in children using language. Current results suggest that key developments occur between the ages of three to five. However, linguistic performance can be misleading as language itself is developing. We therefore advocate the use of methodologies that focus on future-oriented action. Mental time travel required profound changes in humans' motivational system, so that current behavior could be directed to secure not just present, but individually anticipated future needs. Such behavior should be distinguishable from behavior based on current drives, or on other mechanisms. We propose an experimental paradigm that provides subjects with an opportunity to act now to satisfy a need not currently experienced. This approach may be used to assess mental time travel in nonhuman animals. We conclude by describing a preliminary study employing an adaptation of this paradigm for children. (c) 2005 Elsevier Inc. All rights reserved.

Twin study of adolescent genetic susceptibility to mosquito bites using ordinal and comparative rating data

Ordinal and comparative rating measures of mosquito attraction and mosquito bite frequency and symptoms were administered in a self-report questionnaire format to a sample of 197 monozygotic and 326 dizygotic Australian adolescent twin pairs at age 12 between 1992 and 1999, in order to investigate the environmental and possibly genetic determinants of variation between individuals. Repeat measures were obtained from the twin pairs at age 14. Ordinal variable measures, although providing some support for genetic effects on mosquito susceptibility, were affected by low repeatability. However, analysis of a comparative rating variable compared with your twin, who is bitten by mosquitoes more often? indicated a strong genetic influence on frequency of being bitten by mosquitoes, with no significant differences observed between males and females. Comparative rating questionnaire items are a potentially valuable tool for complementing and improving the results obtained from more conventional absolute measures. (C) 2000 Wiley-Liss, Inc.

Expression of multilectin receptors and comparative FITC-dextran uptake by human dendritic cells

Dendritic cells (DC) are potent antigen-presenting cells and understanding their mechanisms of antigen uptake is important for loading DC with antigen for immunotherapy. The multilectin receptors, DEC-205 and macrophage mannose receptor (MMR), are potential antigen-uptake receptors; therefore, we examined their expression and FITC-dextran uptake by various human DC preparations. The RT-PCR analysis detected low levels of DEC-205 mRNA in immature blood DC, Langerhans cells (LC) and immature monocyte-derived DC (Mo-DC), Its mRNA expression increased markedly upon activation, indicating that DEC-205 is an activation-associated molecule. In Mo-DC, the expression of cell-surface DEC-205 increased markedly during maturation. In blood DC, however, the cell-surface expression of DEC-205 did not change during activation, suggesting the presence of a large intracellular pool of DEC-205 or post-transcriptional regulation. Immature Mo-DC expressed abundant MMR, but its expression diminished upon maturation. Blood DC and LC did not express detectable levels of the MMR, FITC-dextran uptake by both immature and activated blood DC was 30- to 70-fold less than that of LC, immature Mo-DC and macrophages. In contrast to immature Mo-DC, the FITC-dextran uptake by LC was not inhibited effectively by mannose, an inhibitor for MMR-mediated FITC-dextran uptake. Thus, unlike Mo-DC, blood DC and LC do not use the MMR for carbohydrate-conjugated antigen uptake and alternative receptors may yet be defined on these DC. Therefore, DEC-205 may have a different specificity as an antigen uptake receptor or contribute to an alternative DC function.

Comparative analysis of prothrombin activators from the venom of Australian elapids

A key component of the venom of many Australian snakes belonging to the elapid family is a toxin that is structurally and functionally similar to that of the mammalian prothrombinase complex. In mammals, this complex is responsible for the cleavage of prothrombin to thrombin and is composed of factor Xa in association with its cofactors calcium, phospholipids, and factor Va. The snake prothrombin activators have been classified on the basis of their requirement for cofactors for activity. The two major subgroups described in Australian elapid snakes, groups C and D, are differentiated by their requirement for mammalian coagulation factor Va. In this study, we describe the cloning, characterization, and comparative analysis of the factor X- and factor V-like components of the prothrombin activators from the venom glands of snakes possessing either group C or D prothrombin activators. The overall domain arrangement in these proteins was highly conserved between all elapids and with the corresponding mammalian clotting factors. The deduced protein sequence for the factor X-like protease precursor, identified in elapids containing either group C or D prothrombin activators, demonstrated a remarkable degree of relatedness to each other (80%-97%). The factor V-like component of the prothrombin activator, present only in snakes containing group C complexes, also showed a very high degree of homology (96%-98%). Expression of both the factor X- and factor V-like proteins determined by immunoblotting provided an additional means of separating these two groups at the molecular level. The molecular phylogenetic analysis described here represents a new approach for distinguishing group C and D snake prothrombin activators and correlates well with previous classifications.

Intraspecific and intraspecific views of colour signals in the strawberry poison frog Dendrobates Pumilio

Poison frogs in the anuran family Dendrobatidae use bright colors on their bodies to advertise toxicity. The species Dendrobates pumilio Schmidt 1858, the strawberry poison frog, shows extreme polymorphism in color and pattern in Panama. It is known that females of D. pumilio preferentially choose mates of their own color morph. Nevertheless, potential predators must clearly see and recognize all color morphs if the aposermatic signaling system is to function effectively. We examined the ability of conspecifics and a model predator to discriminate a diverse selection of D. pumilio colors from each other and from background colors. Microspectrophotometry of isolated rod and cone photoreceptors of D. pumilio revealed the presence of a trichromatic photopic visual system. A typical tetrachromatic bird system was used for the model predator. Reflectance spectra of frog and background colors were obtained, and discrimination among spectra in natural illuminants was mathematically modeled. The results revealed that both D. pumilio and the model predator discriminate most colors quite well, both from each other and from typical backgrounds, with the predator generally performing somewhat better than the conspecifics. Each color morph displayed at least one color signal that is highly visible against backgrounds to both visual systems. Our results indicate that the colors displayed by the various color morphs of D. pumilio are effective signals both to conspecifics and to a model predator.

Mammalian GRIP domain proteins differ in their membrane binding properties and are recruited to distinct domains of the TGN

The four mammalian golgins, p230/golgin-245, golgin-97, GCC88 and GCC185 are targeted to trans-Golgi network ITGN) membranes by their C-terminal GRIP domain in a G-protein-dependent process. The Arf-like GTPase, Arl1, has been shown to mediate TGN recruitment of p230/golgin245 and golgin-97 by interaction with their GRIP domains; however, it is not known whether all the TGN golgins bind to Arl1 and whether they are all recruited to the same or different TGN domains. Here we demonstrate differences in membrane binding properties and TGN domain recruitment of the mammalian GRIP domain proteins. Overexpression of full-length GCC185 resulted in the appearance of small punctate structures dispersed in the cytoplasm of transfected cells that were identified as membrane tubular structures by immunoelectron microscopy. The cytoplasmic GCC185-labelled structures were enriched for membrane binding determinants of GCC185 GRIP, whereas the three other mammalian GRIP family members did not colocalize with the GCC185-labelled structures. These GCC185-labelled structures included the TGN resident protein alpha2,6 sialyltransferase and excluded the recycling TGN protein, TGN46. The Golgi stack was unaffected by overexpression of GCC185. Overexpression of both full-length GCC185 and GCC88 showed distinct and nonoverlapping structures. We also show that the GRIP domains of GCC185 and GCC88 differ in membrane binding properties from each other and, in contrast to p230/golgin245 and golgin-97, do not interact with Arl1 in vivo. Collectively these results show that GCC88, GCC185 and p230/golgin245 are recruited to functionally distinct domains of the TGN and are likely to be important for the maintenance of TGN subdomain structure, a critical feature for mediating protein sorting and membrane transport.

Antigenic and genetic typing of Whataroa viruses in Australia

We recently characterized three novel alphaviruses isolated from mosquitoes captured in New South Wales, Australia. Initial cross-neutralization studies revealed antigenic similarity to the Sindbis virus (SINV)-like Whataroa virus (WHAV), heretofore found only in New Zealand. Nucleotide sequence analysis showed that the WHAV-Iike viruses shared >99% nucleotide sequence similarity with each other, and 96-97% similarity with prototype WHAV. Enzyme-linked immunosorbent assay reactions of a panel of monoclonal antibodies to SINV showed that the novel WHAV-Iike viruses displayed identical binding patterns and were antigenically distinct from all SINV isolates examined. Although these viruses displayed a similar binding pattern to prototype WHAV, three monoclonal antibodies discriminated them from the New Zealand virus. Our results suggest that these novel alphaviruses are antigenic variants of WHAV and represent the first reported isolations of this virus from outside New Zealand. The monoclonal antibodies used in this study will be useful for typing new SINV and SINV-like isolates.