Physical forces determining the persistency and centring precision of microtubule asters

International audienceHow large cellular structures move purposefully in a crowded and fluctuating cytoplasm remains unclear. In early embryos, microtubule asters can reach hundreds of micrometers and move at high speeds to find the geometrical center of large egg and blastomere cells, a process essential for the fidelity of cell division and development. Aster centration in these cells therefore represents a prime and ubiquitous example of directed cytoskeletal motion with acute physiological constraints on precision. We found that positional fluctuations of migrating sea urchin sperm asters were small, anisotropic, and associated with the stochasticity of dynein-dependent forces moving the aster. Using in vivo magnetic tweezers to directly measure aster forces inside cells, we derived a linear aster force-velocity relationship and evidenced a spring-like active mechanism stabilizing aster transverse position. The large frictional coefficient and spring constant quantitatively accounted for the amplitude and growth characteristics of athermal positional fluctuations, demonstrating that aster mechanics ensure noise-suppression to promote persistent and precise centration. These findings define generic biophysical regimes of active cytoskeletal mechanics underlying the accuracy of cell division and early embryonic development

High-NaCl perception in drosophila melanogaster

Salt is a fundamental nutrient that is required for many physiological processes, including electrolyte homeostasis and neuronal activity. In mammals and Drosophila, the detection of NaCl induces two different behaviors: low-salt concentrations provide an attractive stimulus, whereas high-salt concentrations are avoided. We identified the gene called serrano (sano) as being expressed in the sensory organs of Drosophila larvae. A transgenic reporter line showed that sano was coexpressed with Gr66a in a subset of gustatory neurons in the terminal organ of third-instar larvae. The disruption of sano gene expression in gustatory neurons led to the specific loss of high-salt concentration avoidance in larvae, whereas the detection of other attractive or aversive substances was unaffected. Moreover, using a cellular marker sensitive to calcium levels, Sano function was shown to be required for neuronal activity in response to high-salt concentrations. In these neurons, the loss of the DEG/ENaC channel PPK19 function also eliminated the cellular response to high-salt concentrations. Our study revealed that PPK19 and Sano are required in the neurons of the larval gustatory organs for the detection of high-salt concentrations

Population genomic evidence that human and animal infections in Africa come from the same populations of Dracunculus medinensis

International audienceBackground: Guinea worm-Dracunculus medinensis-was historically one of the major parasites of humans and has been known since antiquity. Now, Guinea worm is on the brink of eradication, as efforts to interrupt transmission have reduced the annual burden of disease from millions of infections per year in the 1980s to only 54 human cases reported globally in 2019. Despite the enormous success of eradication efforts to date, one complication has arisen. Over the last few years, hundreds of dogs have been found infected with this previously apparently anthroponotic parasite, almost all in Chad. Moreover, the relative numbers of infections in humans and dogs suggests that dogs are currently the principal reservoir on infection and key to maintaining transmission in that country.Principal findings: In an effort to shed light on this peculiar epidemiology of Guinea worm in Chad, we have sequenced and compared the genomes of worms from dog, human and other animal infections. Confirming previous work with other molecular markers, we show that all of these worms are D. medinensis, and that the same population of worms are causing both infections, can confirm the suspected transmission between host species and detect signs of a population bottleneck due to the eradication efforts. The diversity of worms in Chad appears to exclude the possibility that there were no, or very few, worms present in the country during a 10-year absence of reported cases.Conclusions: This work reinforces the importance of adequate surveillance of both human and dog populations in the Guinea worm eradication campaign and suggests that control programs aiming to interrupt disease transmission should stay aware of the possible emergence of unusual epidemiology as pathogens approach elimination