Alexandra Pieltain

A novel high efficiency, low maintenance, hydroponic system for synchronous growth and flowering of Arabidopsis thaliana.

BackgroundArabidopsis thaliana is now the model organism for genetic and molecular plant studies, but growing conditions may still impair the significance and reproducibility of the experimental strategies developed. Besides the use of phytotronic cabinets, controlling plant nutrition may be critical and could be achieved in hydroponics. The availability of such a system would also greatly facilitate studies dealing with root development. However, because of its small size and rosette growth habit, Arabidopsis is hardly grown in standard hydroponic devices and the systems described in the last years are still difficult to transpose at a large scale. Our aim was to design and optimize an up-scalable device that would be adaptable to any experimental conditions.ResultsAn hydroponic system was designed for Arabidopsis, which is based on two units: a seed-holder and a 1-L tank with its cover. The original agar-containing seed-holder allows the plants to grow from sowing to seed set, without transplanting step and with minimal waste. The optimum nitrate supply was determined for vegetative growth, and the flowering response to photoperiod and vernalization was characterized to show the feasibility and reproducibility of experiments extending over the whole life cycle. How this equipment allowed to overcome experimental problems is illustrated by the analysis of developmental effects of nitrate reductase deficiency in nia1nia2 mutants.ConclusionThe hydroponic device described in this paper allows to drive small and large scale cultures of homogeneously growing Arabidopsis plants. Its major advantages are its flexibility, easy handling, fast maintenance and low cost. It should be suitable for many experimental purposes.

Activation of latent DNA-replication origins : a universal effect of cytokinins

In a previous study (Houssa et al., 1990, Planta 181, 324–326) we observed that a single application of a low dose of benzylaminopurine, a cytokinin, resulted in the halving of the size of the units of DNA replication in the vegetative shoot meristem of Sinapis alba L., a dicotyledonous plant. The effect was due to the recruitment by the hormone of latent replication origins in the chromosomal DNA. Here we report that benzylaminopurine has the same effect in both the vegetative shoot meristem of a monocotyledonous species, Lolium temulentum L., and the tomato (Lycopersicon esculentum Mill.) ovule, a dicotyledonous reproductive meristem. It is thus tentatively concluded that activation of latent replication origins is an universal effect of cytokinins in the regulation of the cell-division cycle.

KIAA1199: A novel regulator of MEK/ERK-induced Schwann cell dedifferentiation

The molecular mechanisms that regulate Schwann cell (SC) plasticity and the role of the Nrg1/ErbB‐induced MEK1/ERK1/2 signalling pathway in SC dedifferentiation or in myelination remain unclear. It is currently believed that different levels of MEK1/ERK1/2 activation define the state of SC differentiation. Thus, the identification of new regulators of MEK1/ERK1/2 signalling could help to decipher the context‐specific aspects driving the effects of this pathway on SC plasticity. In this perspective, we have investigated the potential role of KIAA1199, a protein that promotes ErbB and MEK1/ERK1/2 signalling in cancer cells, in SC plasticity. We depleted KIAA1199 in the SC‐derived MSC80 cell line with RNA‐interference‐based strategy and also generated Tamoxifen‐inducible and conditional mouse models in which KIAA1199 is inactivated through homologous recombination, using the Cre‐lox technology. We show that the invalidation of KIAA1199 in SC decreases the expression of cJun and other negative regulators of myelination and elevates Krox20, driving them towards a pro‐myelinating phenotype. We further show that in dedifferentiation conditions, SC invalidated for KIAA1199 exhibit lower myelin clearance as well as increased myelination capacity. Finally, the Nrg1‐induced activation of the MEK/ERK/1/2 pathway is severely reduced when KIAA1199 is absent, indicating that KIAA1199 promotes Nrg1‐dependent MEK1 and ERK1/2 activation in SCs. In conclusion, this work identifies KIAA1199 as a novel regulator of MEK/ERK‐induced SC dedifferentiation and contributes to a better understanding of the molecular control of SC dedifferentiation.