Nucleoporin98-96 Function Is Required for Transit Amplification Divisions in the Germ Line of Drosophila melanogaster

Production of specialized cells from precursors depends on a tightly regulated sequence of proliferation and differentiation steps. In the gonad of Drosophila melanogaster, the daughters of germ line stem cells (GSC) go through precisely four rounds of transit amplification divisions to produce clusters of 16 interconnected germ line cells before entering a stereotypic differentiation cascade. Here we show that animals harbouring a transposon insertion in the center of the complex nucleoporin98-96 (nup98-96) locus had severe defects in the early steps of this developmental program, ultimately leading to germ cell loss and sterility. A phenotypic analysis indicated that flies carrying the transposon insertion, designated nup98-962288, had dramatically reduced numbers of germ line cells. In contrast to controls, mutant testes contained many solitary germ line cells that had committed to differentiation as well as abnormally small clusters of two, four or eight differentiating germ line cells. This indicates that mutant GSCs rather differentiated than self-renewed, and that these GSCs and their daughters initiated the differentiation cascade after zero, or less than four rounds of amplification divisions. This phenotype remained unaffected by hyper-activation of signalling pathways that normally result in excessive proliferation of GSCs and their daughters. Expression of wildtype nup98-96 specifically in the germ line cells of mutant animals fully restored development of the GSC lineage, demonstrating that the effect of the mutation is cell-autonomous. Nucleoporins are the structural components of the nucleopore and have also been implicated in transcriptional regulation of specific target genes. The nuclear envelopes of germ cells and general nucleocytoplasmic transport in nup98-96 mutant animals appeared normal, leading us to propose that Drosophila nup98-96 mediates the transport or transcription of targets required for the developmental timing between amplification and differentiation

Regulation of cAMP and GSK3 signaling pathways contributes to the neuronal conversion of glioma

Glioma is the most malignant type of primary central nervous system tumors, and has an extremely poor prognosis. One potential therapeutic approach is to induce the terminal differentiation of glioma through the forced expression of pro-neural factors. Our goal is to show the proof of concept of the neuronal conversion of C6 glioma through the combined action of small molecules. We investigated the various changes in gene expression, cell-specific marker expression, signaling pathways, physiological characteristics, and morphology in glioma after combination treatment with two small molecules (CHIR99021, a glycogen synthase kinase 3 [GSK3] inhibitor and forskolin, a cyclic adenosine monophosphate [cAMP] activator). Here, we show that the combined action of CHIR99021 and forskolin converted malignant glioma into fully differentiated neurons with no malignant characteristics; inhibited the proliferation of malignant glioma; and significantly down-regulated gene ontology and gene expression profiles related to cell division, gliogenesis, and angiogenesis in small molecule-induced neurons. In vivo, the combined action of CHIR99021 and forskolin markedly delayed neurological deficits and significantly reduced the tumor volume. We suggest that reprogramming technology may be a potential treatment strategy replacing the therapeutic paradigm of traditional treatment of malignant glioma, and a combination molecule comprising a GSK3 inhibitor and a cAMP inducer could be the next generation of anticancer drugs

Genetic and Chemical Modifiers of a CUG Toxicity Model in Drosophila

Non-coding CUG repeat expansions interfere with the activity of human Muscleblind-like (MBNL) proteins contributing to myotonic dystrophy 1 (DM1). To understand this toxic RNA gain-of-function mechanism we developed a Drosophila model expressing 60 pure and 480 interrupted CUG repeats in the context of a non-translatable RNA. These flies reproduced aspects of the DM1 pathology, most notably nuclear accumulation of CUG transcripts, muscle degeneration, splicing misregulation, and diminished Muscleblind function in vivo. Reduced Muscleblind activity was evident from the sensitivity of CUG-induced phenotypes to a decrease in muscleblind genetic dosage and rescue by MBNL1 expression, and further supported by the co-localization of Muscleblind and CUG repeat RNA in ribonuclear foci. Targeted expression of CUG repeats to the developing eye and brain mushroom bodies was toxic leading to rough eyes and semilethality, respectively. These phenotypes were utilized to identify genetic and chemical modifiers of the CUG-induced toxicity. 15 genetic modifiers of the rough eye phenotype were isolated. These genes identify putative cellular processes unknown to be altered by CUG repeat RNA, and they include mRNA export factor Aly, apoptosis inhibitor Thread, chromatin remodelling factor Nurf-38, and extracellular matrix structural component Viking. Ten chemical compounds suppressed the semilethal phenotype. These compounds significantly improved viability of CUG expressing flies and included non-steroidal anti-inflammatory agents (ketoprofen), muscarinic, cholinergic and histamine receptor inhibitors (orphenadrine), and drugs that can affect sodium and calcium metabolism such as clenbuterol and spironolactone. These findings provide new insights into the DM1 phenotype, and suggest novel candidates for DM1 treatments

New Insights on Betic Cordillera Structure from Gas Geochemistry

International audienceThe current lithospheric structure of the Betic Cordillera results from active geodynamic system related to slab retreat slowdown in western Mediterranean. A sharp change in lithospheric thickness has been imaged beneath the Betic Cordillera, potentially resulting from a near‐vertical subduction‐transform‐edge‐propagator fault (STEP) towards the surface with possible mantle influx. In this study, we use helium isotopic composition of bubbling and dissolved gases in groundwater samples of the central part of the Betic Cordillera to evaluate the origin of gases and to set constraints on its lithospheric structure. We found that helium isotopic composition have a dominant radiogenic component with a mantle‐derived He contribution reaching mainly 1 % for the investigated area. Estimation of He diffusion within the ductile crust indicates that this process is potentially to slow to explain the low mantle‐derived He contribution measured at the surface. A new analysis of the available data of the crustal metamorphic complexes allows us to suggest that the crust could be dissociated from the mantle with no evidence of asthenospheric influx. The weak mantle He signature could reflect a mantle material earlier incorporated in the crustal metamorphic complexes of the Betic Cordillera during their exhumation. In light of mass‐balance calculations, we propose that the slight 3He excess observed in the present‐day fluids might result from a fossil mantle signature diluted by local radiogenic production over time

Role of CO2 in low to medium enthalpy geothermal systems in the Central Betic Cordillera (Spain)

International audienceThere is growing interest in geothermal energy, which is considered as an efficient energy solution to mitigate rising atmospheric CO2. Besides known high enthalpy geothermal systems, increasing attention is paid to low temperature geothermal systems, as they are suitable for local use. Although geothermal production seems to be an environmentally advantageous renewable energy, it might result in significant CO2 emissions. In this study, we investigate the relationship between temperature, fugacity of CO2 (fCO2), and mineral buffers in the reservoir conditions, taking the low- to medium- enthalpy thermal waters in the Central Betic Cordillera as case study. Using geochemical modeling, three main groups of waters have been identified depending on temperature, buffering mineral assemblage, and fCO2 in their reservoir. A group of waters with a reservoir temperature ranging from 70 to 90 °C and located in the intramountain sedimentary basins shows a fCO2 in depth ranging from ~6 × 10−2 and 6 × 10−1. The reservoir chemistry of this water group seems to be mainly controlled by carbonates and evaporites displaying a fCO2 variation between depth and surface (ΔfCO2) of 10−1. Another intermediate group of waters, located in an active extension zone, displays lower temperature (50–60 °C) and fCO2 in the reservoir (from 10−3 to 10−2). Finally, the third group of waters, located on the metamorphic complexes contacts, show the highest estimated temperatures (130–140 °C) and fCO2 in the reservoir (1 to 102). The two latter groups suggest increasing buffering effect of alumino-silicates, in addition to carbonates and quartz. Therefore, we evidenced a strong relationship between temperature and fCO2 in the reservoir as well as the potential mineral buffers. We discussed the potential of geothermal systems as clean energy source based on the estimation of the CO2 emissions generated by the investigated thermal systems for a practical case of household heating

New Insights on Betic Cordillera Structure From Gas Geochemistry

International audienceThe current lithospheric structure of the Betic Cordillera results from active geodynamic system related to slab retreat slowdown in western Mediterranean. A sharp change in lithospheric thickness has been imaged beneath the Betic Cordillera, potentially resulting from a near-vertical subduction-transform-edge-propagator fault toward the surface with possible mantle influx. In this study, we use helium isotopic composition of bubbling and dissolved gases in groundwater samples of the central part of the Betic Cordillera to evaluate the origin of gases and to set constraints on its lithospheric structure. We found that helium isotopic composition have a dominant radiogenic component with a mantle-derived He contribution reaching mainly 1% for the investigated area. Estimation of He diffusion within the ductile crust indicates that this process is potentially to slow to explain the low mantle-derived He contribution measured at the surface. A new analysis of the available data of the crustal metamorphic complexes allows us to suggest that the crust could be dissociated from the mantle with no evidence of asthenospheric influx. The weak mantle He signature could reflect a mantle material earlier incorporated in the crustal metamorphic complexes of the Betic Cordillera during their exhumation. In light of mass balance calculations, we propose that the slight 3 He excess observed in the present-day fluids might result from a fossil mantle signature diluted by local radiogenic production over time

Two-branch break-up systems by a single mantle plume: Insights from numerical modeling

International audienceThermomechanical modeling of plume-induced continental break-up reveals that the initial location of a mantle anomaly relative to a lithosphere inhomogeneity has a major impact on the geometry and timing of a rift-to-spreading system. Models with a warmer Moho temperature are more likely to result in “plume-centered” mode, where the rift and subsequent spreading axis grow directly above the plume. Models with weak far-field forcing are inclined to develop a “structural-inherited” mode, with lithosphere deformation localized at the lateral lithospheric boundary. Models of a third group cultivate two break-up branches (both “plume-centered” and “structural inherited”) that form consecutively with a few million years delay. With our experimental setup, this break-up mode is sensitive to relatively small lateral variations of the initial anomaly position. We argue that one single mantle anomaly can be responsible for nonsimultaneous initiation and development of two rift-to-spreading systems in a lithosphere with a lateral strength contrast