Reduced fertility of female mice lacking CD81

In somatic cells, the tetraspanins CD81 and CD9 associate with each other, with additional tetraspanins and with non-tetraspanin molecules to form proteolipidic complexes. Here we show that CD81 is expressed on the surface of oocytes where it associates with tetraspanin-enriched membrane structures. A major CD9 and CD81 partner, CD9P-1, is also expressed by oocytes. Deletion of CD81 gene in mice results in a 40% reduction of female fertility. In vitro insemination indicated that this infertility is due to a deficiency of oocytes to fuse with sperm. While the fertility of CD9-/- mice is severely but not completely impaired, double knock-out CD9-/- CD81-/- mice were completely infertile indicating that CD9 and CD81 play complementary roles in sperm-egg fusion. Finally, a fraction of CD9 was transferred from CD81-/- oocytes to sperm present in the perivitelline space indicating that the defect of fusion of CD81-/- oocytes does not result from an impaired initial gamete interaction.     

Population demography and the evolution of helping behaviors

Limited dispersal may favor the evolution of helping behaviors between relatives as it increases their relatedness, and it may inhibit such evolution as it increases local competition between these relatives. Here, we explore one way out of this dilemma: if the helping behavior allows groups to expand in size, then the kin-competition pressure opposing its evolution can be greatly reduced. We explore the effects of two kinds of stochasticity allowing for such deme expansion. First, we study the evolution of helping under environmental stochasticity that may induce complete patch extinction. Helping evolves if it results in a decrease in the probability of extinction or if it enhances the rate of patch recolonization through propagules formed by fission of nonextinct groups. This mode of dispersal is indeed commonly found in social species. Second, we consider the evolution of helping in the presence of demographic stochasticity. When fecundity is below its value maximizing deme size (undersaturation), helping evolves, but under stringent conditions unless positive density dependence (Allee effect) interferes with demographic stochasticity. When fecundity is above its value maximizing deme size (oversaturation), helping may also evolve, but only if it reduces negative density-dependent competition.     

Modulating the expression of aquaporin genes in planta: A key to understand their physiological functions?

Aquaporins (AQPs) are believed to act as "cellular plumbers", allowing plants to rapidly alter their membrane water permeability in response to environmental cues. This study of AQP regulation at both the RNA and protein levels has revealed a large number of possible mechanisms. Currently, modulation of AQP expression in planta is considered the strategy of choice for elucidating the role of AQPs in plant physiology. This review highlights the fact that this strategy is complicated by many factors, such as the incomplete characterization of transport selectivity of the targeted AQP, the fact that AQPs might act as multifunctional channels with multiple physiological roles, and the number of post-translational regulation mechanisms. The classification of AQPs as constitutive or stress-responsive isoforms is also proposed.     

Biophysical studies of the interactions between 14-mer and 21-mer model amphipathic peptides and membranes: insights on their modes of action

We have investigated the interactions between synthetic amphipathic peptides and zwitterionic model membranes. Peptides with 14 and 21 amino acids composed of leucines and phenylalanines modified by the addition of crown ethers have been synthesized. The 14-mer and 21-mer peptides both possess a helical amphipathic structure as revealed by circular dichroism. To shed light on their mechanism of membrane interaction, different complementary biophysical techniques have been used such as circular dichroism, fluorescence, membrane conductivity measurement and NMR spectroscopy. Results obtained by these different techniques show that the 14-mer peptide is a membrane perturbator that facilitate the leakage of species such as calcein and Na ions, while the 21-mer peptide acts as an ion channel. (31)P solid-state NMR experiments on multilamellar vesicles reveal that the dynamics and/or orientation of the polar headgroups are greatly affected by the presence of the peptides. Similar results have also been obtained in mechanically oriented DLPC and DMPC bilayers where different acyl chain lengths seem to play a role in the interaction. On the other hand, (2)H NMR experiments on multilamellar vesicles demonstrate that the acyl chain order is affected differently by the two peptides. Based on these studies, mechanisms of action are proposed for the 14-mer and 21-mer peptides with zwitterionic membranes.     

Phosphoprotein enriched in astrocytes-15 kDa expression inhibits astrocyte migration by a protein kinase C delta-dependent mechanism

Phosphoprotein enriched in astrocytes-15 kDa (PEA-15), a phosphoprotein enriched in astrocytes, inhibits both apoptosis and proliferation in normal and cancerous cells. Here, analysis of PEA-15 expression in glioblastoma organotypic cultures revealed low levels of PEA-15 in tumor cells migrating away from the explants, regardless of the expression levels in the originating explants. Because glioblastomas are highly invasive primary brain tumors that can originate from astrocytes, we explored the involvement of PEA-15 in the control of astrocyte migration. PEA-15-/- astrocytes presented an enhanced motility in vitro compared with their wild-type counterparts. Accordingly, NIH-3T3 cells transfected by green fluorescent protein-PEA-15 displayed a reduced migration. Reexpression of PEA-15 restored PEA-15-/- astrocyte motility to wild-type levels. Pharmacological manipulations excluded a participation of extracellular signal-regulated kinase/mitogen-activated protein kinase, phosphatidylinositol 3-kinase/Akt, and calcium/calmodulin-dependent protein kinase II in this effect of PEA-15. In contrast, treatment by bisindolylmaleimide, G?6976, and rottlerin, and chronic application of phorbol 12-myristate 13-acetate and/or bryostatin-1 indicated that PKC delta mediated PEA-15 inhibition of astrocyte migration. PEA-15-/- astrocytes constitutively expressed a 40-kDa form of PKC delta that was down-regulated upon PEA-15 reexpression. Together, these data reveal a new function for PEA-15 in the inhibitory control of astrocyte motility through a PKC delta-dependent pathway involving the constitutive expression of a catalytic fragment of PKC delta.     

Automated scanning for phylogenetically informative transposed elements in rodents

Transposed elements constitute an attractive, useful source of phylogenetic markers to elucidate the evolutionary history of their hosts. Frequent and successive amplifications over evolutionary time are important requirements for utilizing their presence or absence as landmarks of evolution. Although transposed elements are well distributed in rodent taxa, the generally high degree of genomic sequence divergence among species complicates our access to presence/absence data. With this in mind we developed a novel, high-throughput computational strategy, called CPAL (Conserved Presence/Absence Locus-finder), to identify genome-wide distributed, phylogenetically informative transposed elements flanked by highly conserved regions. From a total of 232 extracted chromosomal mouse loci we randomly selected 14 of these plus 2 others from previous test screens and attempted to amplify them via PCR in representative rodent species. All loci were amplifiable and ultimately contributed 31 phylogenetically informative markers distributed throughout the major groups of Rodentia.     

Guidelines: From artificial evolution to computational evolution: a research agenda

Computational scientists have developed algorithms inspired by natural evolution for at least 50 years. These algorithms solve optimization and design problems by building solutions that are 'more fit' relative to desired properties. However, the basic assumptions of this approach are outdated. We propose a research programme to develop a new field: computational evolution. This approach will produce algorithms that are based on current understanding of molecular and evolutionary biology and could solve previously unimaginable or intractable computational and biological problems.     

Spatial normalization of array-CGH data

Background  

Array-based comparative genomic hybridization (array-CGH) is a recently developed technique for analyzing changes in DNA copy number. As in all microarray analyses, normalization is required to correct for experimental artifacts while preserving the true biological signal. We investigated various sources of systematic variation in array-CGH data and identified two distinct types of spatial effect of no biological relevance as the predominant experimental artifacts: continuous spatial gradients and local spatial bias. Local spatial bias affects a large proportion of arrays, and has not previously been considered in array-CGH experiments.     

One-pot synthesis of pegylated ultrasmall iron-oxide nanoparticles and their in vivo evaluation as magnetic resonance imaging contrast agents

A well-defined copolymer poly(oligo(ethylene glycol) methacrylate-co-methacrylic acid) P(OEGMA-co-MAA) was studied as a novel water-soluble biocompatible coating for superparamagnetic iron oxide nanoparticles. This copolymer was prepared via a two-step procedure: a well-defined precursor poly(oligo(ethylene glycol) methacrylate-co-tert-butyl methacrylate), P(OEGMA-co-tBMA) (M(n) = 17300 g mol(-1); M(w)/M(n) = 1.22), was first synthesized by atom-transfer radical polymerization in the presence of the catalyst system copper(I) chloride/2,2'-bipyridyl and subsequently selectively hydrolyzed in acidic conditions. The resulting P(OEGMA-co-MAA) was directly utilized as a polymeric stabilizer in the nanoparticle synthesis. Four batches of ultrasmall PEGylated magnetite nanoparticles (i.e., with an average diameter below 30 nm) were prepared via aqueous coprecipitation of iron salts in the presence of variable amounts of P(OEGMA-co-MAA). The diameter of the nanoparticles could be easily tuned in the range 10-25 nm by varying the initial copolymer concentration. Moreover, the formed PEGylated ferrofluids exhibited a long-term colloidal stability in physiological buffer and could therefore be studied in vivo by magnetic resonance (MR) imaging. Intravenous injection into rats showed no detectable signal in the liver within the first 2 h. Maximum liver accumulation was found after 6 h, suggesting a prolongated circulation of the nanoparticles in the bloodstream as compared to conventional MR imaging contrast agents.