µ-Calpain Conversion of Antiapoptotic Bfl-1 (BCL2A1) into a Prodeath Factor Reveals Two Distinct alpha-Helices Inducing Mitochondria-Mediated Apoptosis

Anti-apoptotic Bfl-1 and pro-apoptotic Bax, two members of the Bcl-2 family sharing a similar structural fold, are classically viewed as antagonist regulators of apoptosis. However, both proteins were reported to be death inducers following cleavage by the cysteine protease µ-calpain. Here we demonstrate that calpain-mediated cleavage of full-length Bfl-1 induces the release of C-terminal membrane active α-helices that are responsible for its conversion into a pro-apoptotic factor. A careful comparison of the different membrane-active regions present in the Bfl-1 truncated fragments with homologous domains of Bax show that helix α5, but not α6, of Bfl-1 induces cell death and cytochrome c release from purified mitochondria through a Bax/Bak-dependent mechanism. In contrast, both helices α5 and α6 of Bax permeabilize mitochondria regardless of the presence of Bax or Bak. Moreover, we provide evidence that the α9 helix of Bfl-1 promotes cytochrome c release and apoptosis through a unique membrane-destabilizing action whereas Bax-α9 does not display such activities. Hence, despite a common 3D-structure, C-terminal toxic domains present on Bfl-1 and Bax function in a dissimilar manner to permeabilize mitochondria and induce apoptosis. These findings provide insights for designing therapeutic approaches that could exploit the cleavage of endogenous Bcl-2 family proteins or the use of Bfl-1/Bax-derived peptides to promote tumor cell clearance

Repeated evolution of fungal cultivar specificity in independently evolved ant-plant-fungus symbioses.

Some tropical plant species possess hollow structures (domatia) occupied by ants that protect the plant and in some cases also provide it with nutrients. Most plant-ants tend patches of chaetothyrialean fungi within domatia. In a few systems it has been shown that the ants manure the fungal patches and use them as a food source, indicating agricultural practices. However, the identity of these fungi has been investigated only in a few samples. To examine the specificity and constancy of ant-plant-fungus interactions we characterised the content of fungal patches in an extensive sampling of three ant-plant symbioses (Petalomyrmex phylax/Leonardoxa africana subsp. africana, Aphomomyrmex afer/Leonardoxa africana subsp. letouzeyi and Tetraponera aethiops/Barteria fistulosa) by sequencing the Internal Transcribed Spacers of ribosomal DNA. For each system the content of fungal patches was constant over individuals and populations. Each symbiosis was associated with a specific, dominant, primary fungal taxon, and to a lesser extent, with one or two specific secondary taxa, all of the order Chaetothyriales. A single fungal patch sometimes contained both a primary and a secondary taxon. In one system, two founding queens were found with the primary fungal taxon only, one that was shown in a previous study to be consumed preferentially. Because the different ant-plant symbioses studied have evolved independently, the high specificity and constancy we observed in the composition of the fungal patches have evolved repeatedly. Specificity and constancy also characterize other cases of agriculture by insects

Spatial distribution of Chaetothyriales MOTUs of the <i>Petalomyrmex phylax/Leonardoxa africana</i> subsp. <i>africana</i> system.

<p>Sectors represent the proportion of each Molecular Operational Taxonomic Unit in each sampling site. MOTUs were detected using universal and/or specific ITS primers. Size of pie charts is proportional to sample size (i.e., the number of fungal samples for which at least one Chaetothyriales MOTU was detected).</p

Sequences of primers developed in this study to amplify specifically the ITS region of fungal Molecular Operational Taxonomic Units (MOTU) detected in two focal ant-plant symbioses.

<p>Sequences of primers developed in this study to amplify specifically the ITS region of fungal Molecular Operational Taxonomic Units (MOTU) detected in two focal ant-plant symbioses.</p

Number of fungal samples in which the different MOTUs were detected using sequencing of the ITS region (ITS1, 5.8S, ITS2) of ribosomal DNA.

a<p>PCR was performed directly on the fungal patch using fungal universal primers ITS1f and ITS4, and thus only one species per sample can be detected.</p>b<p>species were detected using either universal primers, molecular cloning of PCR product or species-specific primers, so that several species per sample can be detected.</p>c<p>either no amplification, or the sequence was not readable.</p>d<p>sequences that do not belong to Chaetothyriales (likely contaminants or non-symbiotic competitors).</p

Spatial distribution of Chaetothyriales MOTUs of the <i>Tetraponera aethiops/Barteria fistulosa</i> system.

<p>Sectors represent the proportion of each Molecular Operational Taxonomic Unit in each sampling site. MOTUs were detected using universal and/or specific ITS primers. When specific ITS primers were used, PCR products were not always sequenced. Size of pie charts is proportional to sample size (i.e., the number of fungal samples for which at least one Chaetothyriales MOTU was detected).</p

Characterization of a general amino acid permease from Hebeloma cylindrosporum

Besides a role in phosphate supply, ectomycorrhizas play a crucial role in nitrogen nutrition of plants. The ectomycorrhizal association between Hebeloma cylindrosporum and Pinus pinaster serves as a model system accessible to molecular manipulation. Hebeloma mycelium is able to take up and use amino acids as the sole nitrogen source. Suppression cloning allowed identification of a Hebeloma transporter (HcGAP1) mediating histidine uptake. HcGAP1 mediates secondary active uptake of a wide spectrum of different amino acids. The secondary active transport mechanism together with the expression in hyphae, but not in mycorrhizas, indicate a role in uptake of organic nitrogen from the soil

Cinescintigraphie renale quantitative a l'hippuran I. Aspects methodologiques, trousse de marquage de l'hippuran

SIGLEAvailable from CEN Saclay, Service de Documentation, 91191 Gif-sur-Yvette Cedex (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc