Dynamic management of genetic resources: maintenance of outcrossing in experimental metapopulations of a predominantly inbreeding species

Dynamic management of genetic resources inpredominantly inbreeding species requiresincreased levels of outcrossing to limit theloss of genetic variation due to smallereffective sizes and to favour the emergence ofnew genetic combinations. Here, we show thatoutcrossing rates can artificially bepermanently increased in experimental evolvingplant metapopulations, using Arabidopsisthaliana as a model. We introducedmale-sterility genes and used an adequatemanagement of the resulting female plants tomodify the outcrossing rates. As expected, theincrease in outcrossing resulted in lowerlevels of heterozygote deficiency (F _is) than observed in natural populationsof A. thaliana and therefore in themaintenance of potentially higher levels ofgenetic variation. An additional selectiveadvantage for females' offspring, due to theproduction of larger seeds by females and apossible heterosis effect, furthermore led tosmaller F _is than expected from therealized outcrossing rate. This selectiveadvantage also resulted in an increase infemale frequency, especially in metapopulationswith large population sizes, creating anon-causal negative correlation between femalefrequency and heterozygote deficiency.     

Complex recombination patterns arising during geminivirus coinfections preserve and demarcate biologically important intra-genome interaction networks

Genetic recombination is an important process during the evolution of many virus species and occurs particularly frequently amongst begomoviruses in the single stranded DNA virus family, Geminiviridae. As in many other recombining viruses it is apparent that non-random recombination breakpoint distributions observable within begomovirus genomes sampled from nature are the product of variations both in basal recombination rates across genomes and in the over-all viability of different recombinant genomes. Whereas factors influencing basal recombination rates might include local degrees of sequence similarity between recombining genomes, nucleic acid secondary structures and genomic sensitivity to nuclease attack or breakage, the viability of recombinant genomes could be influenced by the degree to which their co-evolved protein-protein and protein-nucleotide and nucleotide-nucleotide interactions are disreputable by recombination. Here we investigate patterns of recombination that occur over 120 day long experimental infections of tomato plants with the begomoviruses Tomato yellow leaf curl virus and Tomato leaf curl Comoros virus. We show that patterns of sequence exchange between these viruses can be extraordinarily complex and present clear evidence that factors such as local degrees of sequence similarity but not genomic secondary structure strongly influence where recombination breakpoints occur. It is also apparent from our experiment that over-all patterns of recombination are strongly influenced by selection against individual recombinants displaying disrupted intra-genomic interactions such as those required for proper protein and nucleic acid folding. Crucially, we find that selection favoring the preservation of co-evolved longer-range protein-protein and protein DNA interactions is so strong that its imprint can even be used to identify the exact sequence tracts involved in these interactions.     

Motor activity and trajectory control during escape jumping in the locust <Emphasis Type="Italic">Locusta migratoria</Emphasis>

We investigated the escape jumps that locusts produce in response to approaching objects. Hindleg muscular activity during an escape jump is similar to that during a defensive kick. Locusts can direct their escape jumps up to 50° either side of the direction of their long axis at the time of hindleg flexion, allowing them to consistently jump away from the side towards which an object is approaching. Variation in jump trajectory is achieved by rolling and yawing movements of the body that are controlled by the fore- and mesothoracic legs. During hindleg flexion, a locust flexes the foreleg ipsilateral to its eventual jump trajectory and then extends the contralateral foreleg. These foreleg movements continue throughout co-contraction of the hindleg tibial muscles, pivoting the locust’s long axis towards its eventual jump trajectory. However, there are no bilateral differences in the motor programs of the left and right hindlegs that correlate with jump trajectory. Foreleg movements enable a locust to control its jump trajectory independent of the hindleg motor program, allowing a decision on jump trajectory to be made after the hindlegs have been cocked in preparation for a jump.     

Spatial and temporal control of expression of therapeutic genes using heat shock protein promoters

Heat-shock protein promoters, particularly hsp70, have been used for gene therapy strategies because of their efficiency and the possibility of induction by external heat. This review describes some of the characteristics of hsp70 promoters that make them attractive for use in gene therapy. The human hsp70B promoter is especially promising because of its dose response effect with regard to temperature. Spatial and temporal control of transgene expression using hsp70 promoters necessitates non-invasive methods of local heat deposition and accurate local control of temperature. Special emphasis is given to Focused Ultrasound heating guided by Magnetic Resonance temperature mapping.     

Long-chain acyl-CoA synthetase 6 preferentially promotes DHA metabolism

Previously we demonstrated that supplementation with the polyunsaturated fatty acids (PUFA) arachidonic acid (AA) or docosahexaenoic acid (DHA) increased neurite outgrowth of PC12 cells during differentiation, and that overexpression of rat acyl-CoA synthetase long-chain family member 6 (Acsl6, formerly ACS2) further increased PUFA-enhanced neurite outgrowth. However, whether Acsl6 overexpression enhanced the amount of PUFA accumulated in the cells or altered the partitioning of any fatty acids into phospholipids (PLs) or triacylglycerides (TAGs) was unknown. Here we show that Acsl6 overexpression specifically promotes DHA internalization, activation to DHA-CoA, and accumulation in differentiating PC12 cells. In contrast, oleic acid (OA) and AA internalization and activation to OA-CoA and AA-CoA were increased only marginally by Acsl6 overexpression. Additionally, the level of total cellular PLs was increased in Acsl6 overexpressing cells when the medium was supplemented with AA and DHA, but not with OA. Acsl6 overexpression increased the incorporation of [(14)C]-labeled OA, AA, or DHA into PLs and TAGs. These results do not support a role for Acsl6 in the specific targeting of fatty acids into PLs or TAGs. Rather, our data support the hypothesis that Acsl6 functions primarily in DHA metabolism, and that its overexpression increases DHA and AA internalization primarily during the first 24 h of neuronal differentiation to stimulate PL synthesis and enhance neurite outgrowth.     

The first head-tailed virus,MFTV1, infecting hyperthermophilic methanogenic deep-sea archaea

Deep-sea hydrothermal vents are inhabited by complex communities of microbes and their viruses. Despite the importance of viruses in controlling the diversity, adaptation and evolution of their microbial hosts, to date, only eight bacterial and two archaeal viruses isolated from abyssal ecosystems have been described. Thus, our efforts focused on gaining new insights into viruses associated with deep-sea autotrophic archaea. Here, we provide the first evidence of an infection of hyperthermophilic methanogenic archaea by a head-tailed virus, Methanocaldococcus fervens tailed virus 1 (MFTV1). MFTV1 has an isometric head of 50 nm in diameter and a 150 nm-long non-contractile tail. Virions are released continuously without causing a sudden drop in host growth. MFTV1 infects Methanocaldococcus species and is the first hyperthermophilic head-tailed virus described thus far. The viral genome is a double-stranded linear DNA of 31 kb. Interestingly, our results suggest potential strategies adopted by the plasmid pMEFER01, carried by M. fervens, to spread horizontally in hyperthermophilic methanogens. The data presented here open a new window of understanding on how the abyssal mobilome interacts with hyperthermophilic marine archaea.     

Mort programmée des cellules germinales testiculaires: causes et mécanismes mis en jeu

Spermatogenesis results from a balance between proliferation and apoptosis. An alteration in this balance could lead to testicular diseases such as testicular tumour or infertility. Apoptosis seem to be important in regulating the processes of spermatogenesis since 60 to 75% of germ cells do not reach the spermatozoa stage. The various molecules of the apoptotic cascade have been detected in rodent or human germ cells, such as effector caspases and upstream proteins from cell death receptor or mitochondrial pathways. One or several different pathways may be involved in the germ cell apoptotic process triggered physiologically, by hormonal deprivation, or by chemical or physical inducers. Finally, caspases appear to play a role in various testicular diseases (particularly infertility).     

Rhizodeposition shapes rhizosphere microbial community structure in organic soil

The aims of the study were to determine group specificity in microbial utilization of root-exudate compounds and whole rhizodeposition; quantify the proportions of carbon acquired by microbial groups from soil organic matter and rhizodeposition, respectively; and assess the importance of root-derived C as a driver of soil microbial community structure. Additions of 13C-labelled root-exudate compounds to organic soil and steady-state labelling of Lolium perenne, coupled to compound-specific isotope ratio mass spectrometry, were used to quantify group-specific microbial utilization of rhizodeposition. Microbial utilization of glucose and fumaric acid was widespread through the microbial community, but glycine was utilized by a narrower range of populations, as indicated by the enrichment of phospholipid fatty acid (PLFA) analysis fractions. In L. perenne rhizospheres, high rates of rhizodeposit utilization by microbial groups showed good correspondence with increased abundance of these groups in the rhizosphere. Although rhizodeposition was not the quantitatively dominant C source for microbes in L. perenne rhizospheres, relative utilization of this C source was an important driver of microbial group abundance in organic soil.