Clathrin: now you see me, now you don't!

Endocytic clathrin-coated vesicles are short-lived transport intermediates that ferry cargo macromolecules rapidly into the cell interior. Recent work from the Kirchhausen laboratory indicates that the lifetime of a coated vesicle is extremely short, and assembly of nascent coats aborts abruptly unless reinforced by additional regulatory inputs, most likely cargo capture.     

GPI-anchored proteins: now you see 'em, now you don't.

Many cell surface proteins are attached to membranes via covalent glycosylphosphatidylinositol (GPI) anchors that are posttranslationally linked to the carboxy-terminus of the protein. Removal of the GPI lipid moieties by enzymes such as GPI-specific phospholipases or by chemical treatments generates a soluble form of the protein that no longer associates with lipid bilayers. We have found that the removal of lipid moieties from the anchor can also have a second, unexpected effect on the antigenicity of a variety of GPI-anchored surface molecules, suggesting that they undergo major conformational changes. Several antibodies raised against GPI-anchored proteins from protozoa and mammalian cells were no longer capable of binding the corresponding antigens once the lipid moieties had been removed. Conversely, antibodies raised against soluble (delipidated) forms reacted poorly with intact GPI-anchored proteins, but showed enhanced binding after treatment with phospholipases. In the light of these findings, we have reevaluated a number of publications on GPI-anchored proteins. Many of the results are best explained by lipid-dependent changes in antigenicity, indicating this might be a widespread phenomenon. Since many pathogen surface proteins are GPI-anchored, researchers should be aware that the presence or absence of the GPI lipid moieties may have a major impact on the host immune response to infection or vaccination.     

Cytogenetic darkroom magic: now you see them, now you don''t.

Customary procedures used to determine chromosomal inheritance do not disclose many of the chromosomal polymorphisms known to be present, resulting in uninformative families. The sequential printing of individual chromosomes presented here is a technique that has increased the number of informative families in our studies. This technique has revealed previously unseen heritable chromosome differences and allowed the designation of parental origin.     

Salmonella: Now you see it,now you don't

Diseases caused by Salmonella species are characterized by bacterial invasion of host cells. Salmonella invasion requires a genetic locus (inv) with homology to bacterial systems involved in specific protein export and organelle assembly. Until recently, the actual Salmonella invasion factors exported or assembled by the inv system remained unidentified. It now appears that Salmonella produces novel appendages upon contact with host cells. These appendages are transient, appearing and disappearing rapidly from the bacterial surface. Appendages are altered in strains unable to invade due to mutations within the inv/spa locus. Therefore, a role for the invasion locus has been identified, providing another example of bacterial pathogens responding to signals provided by the host cell surface.     

Host‐associated genomic differentiation in congeneric butterflies: now you see it,now you do not

Ecotypic variation among populations may become associated with widespread genomic differentiation, but theory predicts that this should happen only under particular conditions of gene flow, selection and population size. In closely related species, we might expect the strength of host‐associated genomic differentiation (HAD) to be correlated with the degree of phenotypic differentiation in host‐adaptive traits. Using microsatellite and Amplified Fragment Length Polymorphism (AFLP) markers, and controlling for isolation by distance between populations, we sought HAD in two congeneric species of butterflies with different degrees of host plant specialization. Prior work on Euphydryas editha had shown strong interpopulation differentiation in host‐adapted traits, resulting in incipient reproductive isolation among host‐associated ecotypes. We show here that Euphydryas aurinia had much weaker host‐associated phenotypic differentiation. Contrary to our expectations, we detected HAD in Euphydryas aurinia, but not in E. editha. Even within an E. aurinia population that fed on both hosts, we found weak but significant sympatric HAD that persisted in samples taken 9 years apart. The finding of significantly stronger HAD in the system with less phenotypic differentiation may seem paradoxical. Our findings can be explained by multiple factors, ranging from differences in dispersal or effective population size, to spatial variation in genomic or phenotypic traits and to structure induced by past histories of host‐adapted populations. Other infrequently measured factors, such as differences in recombination rates, may also play a role. Our result adds to recent work as a further caution against assumptions of simple relationships between genomic and adaptive phenotypic differentiation.     

Now you see him, now you don't: experience, not age, is related to reproduction in kittiwakes

In long-lived species, individuals can skip reproduction. The proportion of breeders affects population growth rate and viability, there is a need to investigate the factors influencing intermittent breeding. The theory predicts that if lack of experience is an important constraint, breeding probabilities should increase with experience for individuals of the same age, whereas under the so-called restraint hypothesis, breeding probabilities should increase with age regardless of experience. However, because the probability of detecting individuals in the wild is generally less than 1, it is difficult to know exactly the number of previous breeding episodes (breeding experience). To cope with this issue, we developed a hidden process model to incorporate experience as a latent state possibly influencing the probability of breeding. Using a 22-year mark-recapture dataset involving 9970 individuals, we analysed simultaneously experience and age effects on breeding probabilities in the kittiwake (Rissa tridactyla). We did not detect an influence of age on adult breeding probabilities. We found that inexperienced birds breed less frequently than experienced birds. Our approach enables us to highlight the key role of experience on adults breeding probabilities and can be used for a wide range of organisms for which detection is less than 1.     

Now you see me,now you don’t: The locomotory activity rhythm of the Asian garden dormouse (Eliomys melanurus) from Saudi Arabia

The locomotory activity rhythms of Asian garden dormice, Eliomys melanurus from Saudi Arabia were investigated under controlled laboratory conditions. Animals were maintained under different lighting conditions for a period of two weeks each. Dormice exhibited predominantly nocturnal activity during the light/dark (LD) (mean % nocturnal activity: 95.5 ± 0.9%) and dark/light (DL) (mean % nocturnal activity: 96.8 ± 0.7%) light cycles. All animals expressed free-running rhythms of locomotor activity when subjected to constant darkness (mean τ: 24h06 ± 0h09). Upon inversion of the LD cycle to DL, activity re-entrained to the new light cycle within 3 days. When the dark component of the day was lengthened to 8L:16D the active time increased significantly from 11h43 ± 0h05 to 13h43 ± 0h22. In contrast, when the dark component was shortened from 12L:12D to16L: 8D, the active time decreased significantly to 7h58 ± 0h04. No difference was apparent in the locomotor activity at 20 and 30 °C however, dormice became very inactive at 10 °C.Overall, locomotor activity patterns of the Asian garden dormouse largely resemble those of other species of dormice. However, Asian garden dormice spent long periods of time inactive both during light and darkness, when exposed to an ambient temperature of 10 °C, which may be related to the dramatic and sudden change in temperature. This period of inactivity may reflect a bout of torpor or the entering into a state of hibernation.     

AIDS now

Two philosphers from the University of Helsinki argue that, despite beliefs to the contrary in the Western world, AIDS is no longer predominantly a problem limited to homosexuals. First they clarify this claim by presenting epidemiological data. They then consider three ethical issues that have resulted from fearful public reaction to the rapid spread of AIDS: discrimination against those infected with the human immunodeficiency virus (HIV); proposed legal restrictions on personal choices, especially sexual; and screening for HIV antibodies without consent. The H?yrys then discuss whether there is a right not to know one's HIV status. Their essay concludes with suggestions of three ways to fight the spread of AIDS that should be implemented immediately: more support for AIDS research, organization of sociomedical actions such as information campaigns to slow the spread of the disease, and enactment of antidiscrimination legislation.