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The dynamics of the cytoplasmic and nuclear Ca2+pools in starfish oocytes arrested at the prophase of the first meiotic division or after induction of meiosis by 1-methyladenine (1-MA) have been studied by confocal microscopy. A 70 kDa fluorescent Ca2+indicator has been injected in either the cytoplasm or the nucleus, and shown to remain restricted to the compartment of injection. 1-MA induced a first Ca2+transient in the cytosol, followed by a nuclear transient, and eventually by a second cytosolic transient. The latter failed to occur if the nuclear peak was suppressed. This required the nuclear injection of antagonists of the inositol 1,4,5-trisphosphate (InsP3) and cyclic-ADPribose (cADPr) Ca2+channels, showing that both channel types were active in the inner envelope membrane. The nuclear injection of the Ca2+channel antagonists affected the process of meiosis reinitiation: in about one third of the injected oocytes no breakdown of the nuclear envelope (GVBD) was observed. In the others, even if GVBD eventually occurred, the intermixing of the nucleoplasm and cytoplasm was inhibited.

The neurodegenerative disease Friedreich's ataxia is caused by lower than normal levels of frataxin, an important protein involved in iron–sulfur (Fe-S) cluster biogenesis. An important step in designing strategies to treat this disease is to understand whether increasing the frataxin levels by gene therapy would simply be beneficial or detrimental, because previous studies, mostly based on animal models, have reported conflicting results. Here, we have exploited an inducible model, which we developed using the CRISPR/Cas9 methodology, to study the effects of frataxin overexpression in human cells and monitor how the system recovers after overexpression. Using new tools, which range from high-throughput microscopy to in cell infrared, we prove that overexpression of the frataxin gene affects the cellular metabolism. It also leads to a significant increase of oxidative stress and labile iron pool levels. These cellular alterations are similar to those observed when the gene is partly silenced, as occurs in Friedreich's ataxia patients. Our data suggest that the levels of frataxin must be tightly regulated and fine-tuned, with any imbalance leading to oxidative stress and toxicity.

Abruzzese: BMS, Novartis, Pfizer, Ariad: Consultancy. Assouline:BMS: Consultancy; Pfizer: Consultancy; Novartis: Consultancy. D'Emilio:Celgene: Research Funding. Dong-Wook:ll-Yang: Consultancy, Honoraria, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis Pharmaceuticals: Consultancy, Honoraria, Research Funding, Speakers Bureau.

No relevant conflicts of interest to declare.