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Mitochondria play a pivotal role in apoptosis in multicellular organisms by releasing apoptogenic factors such as cytochrome c that activate the caspases effector pathway, and apoptosis-inducing factor (AIF) that is involved in a caspase-independent cell death pathway. Here we report that cell death in the single-celled organism Dictyostelium discoideum involves early disruption of mitochondrial transmembrane potential (⌬⌿m) that precedes the induction of several apoptosis-like features, including exposure of the phosphatidyl residues at the external surface of the plasma membrane, an intense vacuolization, a fragmentation of DNA into large fragments, an autophagy, and the release of apoptotic corpses that are engulfed by neighboring cells. We have cloned a Dictyostelium homolog of mammalian AIF that is localized into mitochondria and is translocated from the mitochondria to the cytoplasm and the nucleus after the onset of cell death. Cytoplasmic extracts from dying Dictyostelium cells trigger the breakdown of isolated mammalian and Dictyostelium nuclei in a cell-free system, and this process is inhibited by a polyclonal antibody specific for Dictyostelium discoideum apoptosis-inducing factor (DdAIF), suggesting that DdAIF is involved in DNA degradation during Dictyostelium cell death. Our findings indicate that the cell death pathway in Dictyostelium involves mitochondria and an AIF homolog, suggesting the evolutionary conservation of at least part of the cell death pathway in unicellular and multicellular organisms. INTRODUCTIONProgrammed cell death (PCD) is a genetically regulated physiological process of cell suicide that is central to the development and homeostasis of multicellular organisms (Raff, 1992;Steller, 1995;Jacobson et al., 1997;Vaux and Korsmeyer, 1999). The basic machinery that controls the onset of PCD in roundworms (Caenorhabditis elegans), insects (Drosophila melanogaster), and vertebrates (mammals) appears to be present in all cells, at all times. Crucial aspects of PCD appear to be conserved, including both the genes encoding the basic cell death machinery, and the morphological and biochemical features of apoptosis, the most frequent phenotype of PCD (Jacobson et al., 1997;Horvitz, 1999;Song and Steller, 1999;Vaux and Korsmeyer, 1999).Mitochondria play a pivotal role in PCD in mammalian cells, in particular through the permeabilization/disruption of their outer membrane, with (or followed by) the loss of mitochondrial transmembrane potential (⌬⌿m) (Kroemer et al., 1995;Green and Reed, 1998;Petit et al., 1998;Goldstein et al., 2000;Martinou et al., 2000), leading to the release of cytochrome c (Liu et al., 1996) and apoptosis-inducing factor # Corresponding author. E-mail address: pxpetit@zeus.cochin.inserm.fr. Abbreviations used: AIF, apoptosis-inducing factor; BSA, bovine serum albumin; DIF-1, differentiation-inducing factor-1; PCR, polymerase chain reaction; ⌬⌿m, mitochondrial transmembrane potential; PCD, programmed cell death; PPIX, protoporphyrin IX; PBS, phosphate-buffered saline. ©...

Photosensitization using the tumor-localizing porphyrin Photofrin induces cell death both in vitro and in vivo, but the mechanism of cell death is not well understood. Cell lysis (necrosis) and apoptosis have both been observed. The latter seems restricted mainly to lymphoma and epithelial cell lines. To check the influence of the incubation protocol on the cell death mechanism, CV-1 cells were loaded with Photofrin using two different protocols. In both protocols, photosensitized CV-1 cells underwent severe morphological changes before cell death. Many cells treated with protocol 1 (24 h with 1 microgram/mL of Photofrin in culture medium) underwent apoptosis, as demonstrated by plasma membrane blebbing and fragmentation into vesicles, condensation of the chromatin and fragmentation of the nucleus with oligonucleosomic degradation of the DNA. In contrast, cells treated with protocol 2 (1 h with 10 micrograms/mL of Photofrin in phosphate-buffered saline) lysed instead of fragmented, without oligonucleosomic degradation of the DNA. This type of cell death looks much like necrosis. However, early morphological changes suggest that it is, in fact, apoptosis stopped by plasma membrane leakage. It is concluded that apoptosis is primarily induced in CV-1 cells but may be arrested by membrane lysis, depending on the incubation protocol.

Recent advances in molecular technology have revolutionized research on all aspects of the biology of organisms, including ciliates, and created unprecedented opportunities for pursuing a more integrative approach to investigations of biodiversity. However, this goal is complicated by large gaps and inconsistencies that still exist in the foundation of basic information about biodiversity of ciliates. The present paper reviews issues relating to the taxonomy of ciliates and presents specific recommendations for best practice in the observation and documentation of their biodiversity. This effort stems from a workshop that explored ways to implement six Grand Challenges proposed by the International Research Coordination Network for Biodiversity of Ciliates (IRCN‐BC). As part of its commitment to strengthening the knowledge base that supports research on biodiversity of ciliates, the IRCN‐BC proposes to populate The Ciliate Guide, an online database, with biodiversity‐related data and metadata to create a resource that will facilitate accurate taxonomic identifications and promote sharing of data.

BackgroundThe pro-apoptotic effector Bid induces mitochondrial apoptosis in synergy with Bax and Bak. In response to death receptors activation, Bid is cleaved by caspase-8 into its active form, tBid (truncated Bid), which then translocates to the mitochondria to trigger cytochrome c release and subsequent apoptosis. Accumulating evidence now indicate that the binding of tBid initiates an ordered sequences of events that prime mitochondria from the action of Bax and Bak: (1) tBid interacts with mitochondria via a specific binding to cardiolipin (CL) and immediately disturbs mitochondrial structure and function idependently of its BH3 domain; (2) Then, tBid activates through its BH3 domain Bax and/or Bak and induces their subsequent oligomerization in mitochondrial membranes. To date, the underlying mechanism responsible for targeting tBid to mitochondria and disrupting mitochondrial bioenergetics has yet be elucidated.Principal FindingsThe present study investigates the mechanism by which tBid interacts with mitochondria issued from mouse hepatocytes and perturbs mitochondrial function. We show here that the helix αH6 is responsible for targeting tBid to mitochondrial CL and disrupting mitochondrial bioenergetics. In particular, αH6 interacts with mitochondria through electrostatic interactions involving the lysines 157 and 158 and induces an inhibition of state-3 respiration and an uncoupling of state-4 respiration. These changes may represent a key event that primes mitochondria for the action of Bax and Bak. In addition, we also demonstrate that tBid required its helix αH6 to efficiently induce cytochrome c release and apoptosis.ConclusionsOur findings provide new insights into the mechanism of action of tBid, and particularly emphasize the importance of the interaction of the helix αH6 with CL for both mitochondrial targeting and pro-apoptotic activity of tBid. These support the notion that tBid acts as a bifunctional molecule: first, it binds to mitochondrial CL via its helix αH6 and destabilizes mitochondrial structure and function, and then it promotes through its BH3 domain the activation and oligomerization of Bax and/or Bak, leading to cytochrome c release and execution of apoptosis. Our findings also imply an active role of the membrane in modulating the interactions between Bcl-2 proteins that has so far been underestimated.

The rate constants of molecular singlet oxygen quenching by saturated and unsaturated fatty-acids and by cholesterol-membrane critical components - membrane critical components - have been measured by time resolved detection of the 1270 nm phosphorescence of singlet molecular oxygen [O2(1deltag)]. We have determined (i) an increment of 5.7 x 10(2)M(-1)s(-1) per -CH2- in C6D6 and CD3OD for saturated fatty acids between C4 and C20, (ii) an increment of 3 x 10(4)M(-1)s(-1) per non-conjugated cis-double bond for C18 unsaturated fatty acids, identical in C6D6 and DC3OD, (iii) a lower quenching rate constant by a factor of 2.7 for the trans-C16 and trans-C18 as compared to the corresponding cis-monounsaturated fatty acids, (iv) a rate constant of O2x(1deltag) quenching by cholesterol of 5.7 x 10(4)M(-1)s(-1) in benzene. These rate constants are compared to those obtained for other membrane cellular components.

We introduce an extension of the linear elastic tensor-mass method which allows fast computation of non-linear and viscoelastic mechanical deformations, and is suitable for the simulation of biological soft tissue deformation. We aim at developing a simulation tool for the planning of cryogenic surgical treatment of liver cancer. Percutaneous surgery simulation requires accurate modeling of the mechanical behavior of soft tissues, and experimental characterizations have shown that linear elasticity is only a coarse approximation of the real properties of biological tissues. We first show that our model can simulate different types of non-linear and viscoelastic mechanical behaviors at speeds which are compatible with real-time applications. Then an experimental setup is presented which was used to characterize the mechanical properties of deer liver tissue under perforation by a biopsy needle. Experimental results demonstrate that a linear model is not suitable for simulating this application while the proposed model succeeds in accurately modeling the mechanical behavior of liver tissue.Résumé. Nous présentons une extension de la méthode des masses-tenseursélastique linéaire permettant le calcul de déformations mécaniques non-linéaires et viscoélastiques, et adaptéeà la simulation de déformations de tissus biologiques mous. Notre objectif est de développer un outil de simulation du traitement du cancer du foie par cryochirurgie. La simulation de chirurgie percutanée nécessite une modélisation précise du comportement mécanique des tissus mous, et plusieurs caractérisations expérimentales ont montré que le modèleélastique linéaire n'était qu'une approximation imprécise des propriétés de tissus biologiques. Nous montrons d'abord que notre modèle peut simuler différents types de comportements mécaniques non-linéaires et viscoélastiquesà des vitesses compatibles avec la construction d'applications en temps réel. Puis nous présentons un montage expérimental utilisé pour caractériser les propriétés mécaniques du foie de cerf lors de la perforation par une aiguilleà biopsie. Les résultats expérimentaux démontrent qu'un modèle linéaire n'est pas adaptéà la simulation d'une telle application, alors que le modèle proposé est capable de reproduire avec précision le comportement mécanique du foie.

Chromidina spp. are enigmatic apostome ciliates (Oligohymenophorea, Opalinopsidae) that parasitise the renal and pancreatic appendages of cephalopods. Only four species have been described, among which only three have been formally named. No DNA sequence has been reported so far. To investigate Chromidina spp. diversity, we sampled cephalopods in the Mediterranean Sea off Tunis, Tunisia, and identified two distinct Chromidina spp. in two different host species: Loligo vulgaris and Sepia officinalis. From haematoxylin-stained slides, we described morphological traits for these parasitic species and compared them to previous descriptions. We also re-described the morphology of Chromidina elegans (Foettinger, 1881) from Chatton and Lwoff’s original materials and designated a neohapantotype and paraneohapantotypes for this species. We describe a new species, Chromidina chattoni Souidenne, Florent and Grellier n. sp., found in L. vulgaris off Tunisia, and evidence for a probable novel species, found in S. officinalis off Tunisia, although this latter species presents similarities to some morphological stages previously described for Chromidina cortezi Hochberg, 1971. We amplified, for the first time, an 18S rDNA marker for these two Chromidina species. Phylogenetic analysis supports the association of Chromidina within apostome ciliates. Genetic distance analysis between 18S rDNA sequences of representative apostomes indicates Pseudocollinia as the most closely related genus to Chromidina.