Browsing by Issue Date, starting with "2014"
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- Androgen modulation of social decision-making mechanisms in the brain: an integrative and embodied perspectivePublication . Oliveira, Gonçalo A.; Oliveira, Rui F.Apart from their role in reproduction androgens also respond to social challenges and this response has been seen as a way to regulate the expression of behavior according to the perceived social environment (Challenge hypothesis, Wingfield et al., 1990). This hypothesis implies that social decision-making mechanisms localized in the central nervous system (CNS) are open to the influence of peripheral hormones that ultimately are under the control of the CNS through the hypothalamic-pituitary-gonadal axis. Therefore, two puzzling questions emerge at two different levels of biological analysis: (1) Why does the brain, which perceives the social environment and regulates androgen production in the gonad, need feedback information from the gonad to adjust its social decision-making processes? (2) How does the brain regulate gonadal androgen responses to social challenges and how do these feedback into the brain? In this paper, we will address these two questions using the integrative approach proposed by Niko Tinbergen, who proposed that a full understanding of behavior requires its analysis at both proximate (physiology, ontogeny) and ultimate (ecology, evolution) levels.
- Daraina sportive lemur (Lepilemur milanoii) density and population size estimates in most of its distribution range: the Loky-Manambato region.Publication . Salmona, J.; Ralantoharijaona, T.; Thani, I.M.; Rakotonanahary, A.; Zaranaina, R.; Jan, F.; Rasolondraibe, E.; Barnavon, M.; Beck, A.; Wholhauser, S.; Ranirison, P.; Zaonarivelo, J.R.; Rabarivola, C.; Chikhi, L.The population of the Daraina sportive lemur (Lepilemur milanoii) is believed to be mostly confined to the Loky-Manambato region (Louis et al., 2006). Very little is known about L. milanoii and it is classified as “Data Deficient” by the IUCN (IUCN, 2013; Schwitzer et al., 2013). Despite the management of the area by the NGO Fanamby since 2005, no study had been conducted to determine the presence and the abundance of L. milanoii in the main forest fragments of the region. During the 2011 dry season we surveyed the ten main forest fragments of the Loky-Manambato region and estimated L. milanoii densities and population sizes using line transect distance sampling (Buckland, 2001) and the DISTANCE software (Thomas et al., 2010). The results suggest that sportive lemur densities are reasonably high in the region, but with important discrepancies between forest fragments, with densities ranging from 49.8 ind./km² in Antsaharaingy to 590.5 ind./km² in Ampondrabe. For the region Loky-Manambato we were able to estimate a population size of 52,000 individuals. This is the first estimate for the total population size and we argue that similar studies should be repeated to monitor environmental changes and anthropogenic pressures (hunting, deforestation, mining, etc.).
- The POU Factor Ventral Veins Lacking/Drifter Directs the Timing of Metamorphosis through Ecdysteroid and Juvenile Hormone SignalingPublication . Cheng, CeCe; Ko, Amy; Chaieb, Leila; Koyama, Takashi; Sarwar, Prioty; Mirth, Christen K.; Smith, Wendy A.; Suzuki, YuichiroAlthough endocrine changes are known to modulate the timing of major developmental transitions, the genetic mechanisms underlying these changes remain poorly understood. In insects, two developmental hormones, juvenile hormone (JH) and ecdysteroids, are coordinated with each other to induce developmental changes associated with metamorphosis. However, the regulation underlying the coordination of JH and ecdysteroid synthesis remains elusive. Here, we examined the function of a homolog of the vertebrate POU domain protein, Ventral veins lacking (Vvl)/Drifter, in regulating both of these hormonal pathways in the red flour beetle, Tribolium castaneum (Tenebrionidae). RNA interference-mediated silencing of vvl expression led to both precocious metamorphosis and inhibition of molting in the larva. Ectopic application of a JH analog on vvl knockdown larvae delayed the onset of metamorphosis and led to a prolonged larval stage, indicating that Vvl acts upstream of JH signaling. Accordingly, vvl knockdown also reduced the expression of a JH biosynthesis gene, JH acid methyltransferase 3 (jhamt3). In addition, ecdysone titer and the expression of the ecdysone response gene, hormone receptor 3 (HR3), were reduced in vvl knockdown larvae. The expression of the ecdysone biosynthesis gene phantom (phm) and spook (spo) were reduced in vvl knockdown larvae in the anterior and posterior halves, respectively, indicating that Vvl might influence ecdysone biosynthesis in both the prothoracic gland and additional endocrine sources. Injection of 20-hydroxyecdysone (20E) into vvl knockdown larvae could restore the expression of HR3 although molting was never restored. These findings suggest that Vvl coordinates both JH and ecdysteroid biosynthesis as well as molting behavior to influence molting and the timing of metamorphosis. Thus, in both vertebrates and insects, POU factors modulate the production of major neuroendocrine regulators during sexual maturation.
- Juvenile hormone regulates body size and perturbs insulin signaling in DrosophilaPublication . Mirth, C. K.; Tang, H. Y.; Makohon-Moore, S. C.; Salhadar, S.; Gokhale, R. H.; Warner, R. D.; Koyama, T.; Riddiford, L. M.; Shingleton, A. W.The role of juvenile hormone (JH) in regulating the timing and nature of insect molts is well-established. Increasing evidence suggests that JH is also involved in regulating final insect size. Here we elucidate the developmental mechanism through which JH regulates body size in developing Drosophila larvae by genetically ablating the JH-producing organ, the corpora allata (CA). We found that larvae that lack CA pupariated at smaller sizes than control larvae due to a reduced larval growth rate. Neither the timing of the metamorphic molt nor the duration of larval growth was affected by the loss of JH. Further, we show that the effects of JH on growth rate are dependent on the forkhead box O transcription factor (FOXO), which is negatively regulated by the insulin-signaling pathway. Larvae that lacked the CA had elevated levels of FOXO activity, whereas a loss-of-function mutation of FOXO rescued the effects of CA ablation on final body size. Finally, the effect of JH on growth appears to be mediated, at least in part, via ecdysone synthesis in the prothoracic gland. These results indicate a role of JH in regulating growth rate via the ecdysone- and insulin-signaling pathways.
- LsrF, a coenzyme A-dependent thiolase, catalyzes the terminal step in processing the quorum sensing signal autoinducer-2Publication . Marques, João C.; Oh, Il Kyu; Ly, Daniel C.; Lamosa, Pedro; Ventura, M. Rita; Miller, Stephen T.; Xavier, Karina BivarThe quorum sensing signal autoinducer-2 (AI-2) regulates important bacterial behaviors, including biofilm formation and the production of virulence factors. Some bacteria, such as Escherichia coli, can quench the AI-2 signal produced by a variety of species present in the environment, and thus can influence AI-2-dependent bacterial behaviors. This process involves uptake of AI-2 via the Lsr transporter, followed by phosphorylation and consequent intracellular sequestration. Here we determine the metabolic fate of intracellular AI-2 by characterizing LsrF, the terminal protein in the Lsr AI-2 processing pathway. We identify the substrates of LsrF as 3-hydroxy-2,4-pentadione-5-phosphate (P-HPD, an isomer of AI-2-phosphate) and coenzyme A, determine the crystal structure of an LsrF catalytic mutant bound to P-HPD, and identify the reaction products. We show that LsrF catalyzes the transfer of an acetyl group from P-HPD to coenzyme A yielding dihydroxyacetone phosphate and acetyl-CoA, two key central metabolites. We further propose that LsrF, despite strong structural homology to aldolases, acts as a thiolase, an activity previously undescribed for this family of enzymes. With this work, we have fully characterized the biological pathway for AI-2 processing in E. coli, a pathway that can be used to quench AI-2 and control quorum-sensing-regulated bacterial behaviors.
- Estimation des densités et tailles de population du Microcèbe Roux du Nord de (Microcebus tavaratra) dans la région Loky-Manambato (Daraina)Publication . Salmona, J.; Rakotonanahary, A.; Thani, I.M.; Zaranaina, R.; Ralantoharijaona, T.; Jan, F.; Rasolondraibe, E.; Barnavon, M.; Beck, A.; Wholhauser, S.; Ranirison, P.; Zaonarivelo, J.R.; Rabarivola, C.; Chikhi, L.La région Loky-Manambato dans le Nord de Madagascar, est connue pour abriter le propithèque à couronne dorée (Propithecus tattersalli), un lémurien emblématique et endémique de la région. Néanmoins cette région composée d’une dizaine de fragments forestiers de taille moyenne et encore relativement peu étudiés, abrite aussi le microcèbe roux du nord (Microcebus tavaratra). Malgré la gestion des forêts de cette région par l’ONG Fanamby depuis 2005, aucune étude n’avait encore été menée dans chacun des fragments forestiers de la région pour déterminer la présence et quantifier la taille des populations de microcèbes de chacun d’entre eux. Lors de notre étude nous avons tenté d’estimer les densités et les tailles des populations de M. tavaratra dans neuf des dix principaux fragments forestiers de la région. Dans ce but nous avons utilisé la méthode de «line transect distance-sampling». Nos résultats montrent que les densités de microcèbes sont relativement élevées, et varient de 28 à 325 ind/km² entre fragments forestiers de la région. Desétudes plus approfondies des données collectées seront nécessaires pour déterminer les variables environnementales responsables des différences de densité observées.
- New density estimates of a threatened sifaka species (Propithecus coquereli) in Ankarafantsika National ParkPublication . Kun-Rodrigues, Célia; Salmona, Jordi; Besolo, Aubin; Rasolondraibe, Emmanuel; Rabarivola, Clément; Marques, Tiago A.; Chikhi, LounèsPropithecus coquereli is one of the last sifaka species for which no reliable and extensive density estimates are yet available. Despite its endangered conservation status [IUCN, 2012] and recognition as a flagship species of the northwestern dry forests of Madagascar, its population in its last main refugium, the Ankarafantsika National Park (ANP), is still poorly known. Using line transect distance sampling surveys we estimated population density and abundance in the ANP. Furthermore, we investigated the effects of road, forest edge, river proximity and group size on sighting frequencies, and density estimates. We provide here the first population density estimates throughout the ANP. We found that density varied greatly among surveyed sites (from 5 to ∼100 ind/km2) which could result from significant (negative) effects of road, and forest edge, and/or a (positive) effect of river proximity. Our results also suggest that the population size may be ∼47,000 individuals in the ANP, hinting that the population likely underwent a strong decline in some parts of the Park in recent decades, possibly caused by habitat loss from fires and charcoal production and by poaching. We suggest community-based conservation actions for the largest remaining population of Coquerel's sifaka which will (i) maintain forest connectivity; (ii) implement alternatives to deforestation through charcoal production, logging, and grass fires; (iii) reduce poaching; and (iv) enable long-term monitoring of the population in collaboration with local authorities and researchers.
- Escherichia coli adaptation to the gut environment: a constant fight for survivalPublication . Gordo, Isabel; Demengeot, Jocelyne; Xavier, Karina
- Controlling Hox gene expression and activity to build the vertebrate axial skeletonPublication . Casaca, Ana; Santos, Ana Cristina; Mallo, MoisésIt has long been known that Hox genes are central players in patterning the vertebrate axial skeleton. Extensive genetic studies in the mouse have revealed that the combinatorial activity of Hox genes along the anterior-posterior body axis specifies different vertebral identities. In addition, Hox genes were instrumental for the evolutionary diversification of the vertebrate body plan. In this review, we focus on fundamental questions regarding the intricate mechanisms controlling Hox gene activity. In particular, we discuss the functional relevance of the precise timing of Hox gene activation in the embryo. Moreover, we provide insight into the epigenetic regulatory mechanisms that are likely to control this process and are responsible for the maintenance of spatially restricted Hox expression domains throughout embryonic development. We also analyze how specific features of each Hox protein may contribute to the functional diversity of Hox family. Altogether, the work reviewed here further supports the notion that the Hox program is far more complex than initially assumed. Exciting new findings will surely emerge in the years ahead.
- Genetic diversity of serotype A foot-and-mouth disease viruses in Kenya from 1964 to 2013; implications for control strategies in eastern AfricaPublication . Wekesa, Sabenzia N.; Sangula, Abraham K.; Belsham, Graham J.; Muwanika, Vincent B.; Heller, Rasmus; Balinda, Sheila N.; Masembe, Charles; Siegismund, Hans R.Serotype A is the most genetically and antigenically diverse of the foot-and-mouth disease virus (FMDV) serotypes. Records of its occurrence in Kenya date back to 1952 and the antigenic diversity of the outbreak viruses in this region is reflected by the current use of two different vaccine strains (K5/1980 and K35/1980) and previous use of two other strains (K18/66 and K179/71). This study aimed at enhancing the understanding of the patterns of genetic variation of serotype A FMDV in Kenya. The complete VP1 coding region sequences of 38 field isolates, identified as serotype A FMDV, collected between 1964 and 2013 were determined. Coalescent-based methods were used to infer times of divergence of the virus strains and the evolutionary rates alongside 27 other serotype A FMDV sequences from Genbank and the World Reference Laboratory (WRL). This study represents the first comprehensive genetic analysis of serotype A FMDVs from Kenya. The study detected four previously defined genotypes/clusters (termed G-I, G-III, G-VII and G-VIII), within the Africa topotype, together with a fifth lineage that has apparently emerged from within G-I; these different lineages have each had a countrywide distribution. Genotypes G-III and G-VIII that were first isolated in 1964 are now apparently extinct; G-VII was last recorded in 2005, while G-I (including the new lineage) is currently in widespread circulation. High genetic diversity, widespread distribution and transboundary spread of serotype A FMDVs across the region of eastern Africa was apparent. Continuous surveillance for the virus, coupled to genetic and antigenic characterization is recommended for improved regional control strategies.