Using clonal cell lines isolated from murine neuroblastoma C1300, we investigated the mitochondrial changes related to neuronal differentiation and, more generally, the role played by the mitochondrion in this phenomenon. By different approaches (measurement of the mitochondrial mass, immunoquantification of specific mitochondrial proteins, or incorporation of Rhodamine 123), the differentiation of the inducible clone, N1E-115, was found associated with an important increase of the cellular content in mitochondria. This increase could be observed with differentiating N1E-115 cells maintained in suspension, i.e. under conditions where neurite outgrowth is prevented but other early stages of (biochemical) differentiation continue to occur. That these mitochondrial changes are likely to be correlated with these stages of neuronal differentiation, rather than with simple progression to the postmitotic stage, stems from comparative experiments with clone N1A-103, a neuroblastoma cell line variant that becomes postmitotic after induction but fails to differentiate and shows no modification in its cellular content in mitochondria. In accordance with these observations, chloramphenicol prevents differentiation when added together with the inducer. This effect is probably related to the inhibition of mitochondrial translation rather than to modification of the bioenergetic needs because oligomycine, a potent inhibitor of the mitochondrial ATP synthetase, shows no effect on neurogenesis. As a working hypothesis and in keeping with independently published models, we postulate that products resulting from mitochondrial translation could be involved in the organization of the cytoskeleton or of certain membrane components whose rearrangements should be the prerequisite or the correlates to early stages of neuronal differentiation.
The evolution of the mitochondrion has been followed within differentiating neuronal cells, both in primary cultures of neurons from fetal rat cortex and during rat brain cortex maturation. Changes in total mitochondrial proteins (mt-proteins) were evaluated, and qualitative changes in the mt-proteins pattern were analyzed using the Western blot technique. The evolution of mt-protein contents in cultured neurons resembles what is observed during rat brain maturation. The mitochondrion exhibits pronounced changes in the course of neurogenesis, in particular, bursts of mitochondrial masses accompanying the successive steps of neurogenesis are observed. There are indications that protein equipment of mitochondria during neuronal development undergoes variations. Although more work is required to establish the significance of these correlations, the present data might suggest an important role of the mitochondrion in neurogenesis.
Nous suivons l'expression de l'oncogene c-myc pendant la maturation du cortex de souris. Par ailleurs, en utilisant le CCA ou le DMSO comme inducteur de différenciation, nous analysons l'expression de c-myc sur deux clones dérivant du neuroblastome murin C1300 : i) le clone N1E 115 qui exprime des marqueurs neuronaux et ii) le clone NIA 103 incapable de se diférencier morphologiquement (M.M. Portier et al. 1982, FEBS 1-ett. 146, 283).-Nous montrons par hybridation sur Northern blot que la sonde c-myc utilisée (D. Montarras et C. Pinset, Institut Pasteur Paris) reconnait une seule bande à 2,4kb, permettant ainsi une étude par hybridation sur Slot blots. Chez la souris, nous observons une diminution entre les 15° et 18° jours de la vie foetale, qui précède une forte expression transitoire au moment de la naissance. Contrai rement à la situation observée dans le clone NIA 103, on décèle une diminution rapide de l'expression de c-myc dans le clone N1E 115 induit. L'expression de l'oncogène c-myc, dont le rôle lors de la division cellulaire est connu, apparait donc corrélée avec la différenciation du neuroblastome. Nous entreprenons une étude par hybridation in situ et par immunofluorescence (anticorps donné par Ph. Amouyel, Institut Pasteur Lille) sur les clones de neuroblastome afin de confirmer ces résultats. Ce travail a été effectué qrâce à l'aide de la Ligue Nationale Française contre le Cance RECEPTEURS NUCLEAIRES DE TR HODOTHYRONINE (RNT3) ET PRODUITS D'EXPRESSION DES ONCOGENES C-ERB A AU COURS
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