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E2F-1 is the prototype of a family of transcription factors playing a central role in the control of cell proliferation and apoptosis. E2F DNA binding activity is down-regulated during cellular differentiation, which is correlated with cell division arrest. We report here that the expression of E2F-1 itself is down-regulated in the developing quail neural retina between embryonic days E8-E10. This event occurs just after the massive arrest of the quail neuroretina cell division (E7-E8). To gain further insight into the regulatory mechanisms monitoring E2F-1 expression in differentiating neurons, we have cloned the quail E2F-1 promoter. In vivo DNA footprintings of this promoter have shown that a number of potential SP-1 and C/EBP response elements are constitutively occupied in the entire quail neuroretina of E5 and E14, whereas the two consensus palindromic E2F binding sites are only protected at E5. This suggests that these E2F elements participate in down-regulation of E2F-1 gene expression during avian neuroretina development. CAT reporter assays have shown that E2F-1 in association with its partner DP-1 transactivates its own promoter, whereas p105Rb inhibits the E2F-1 promoter. Both E2F-1/DP-1 and p105Rh require the presence of the E2F binding sites to mediate their effects. However, experiments performed with deletion mutants of the promoter strongly suggest that other regions located upstream of the E2F binding sites also mediate part of the E2F-1 transactivating effect on its own promoter. Altogether, these results suggest that the down-regulation of E2F-1 gene expression in differentiating neurons could be due, in part, to the E2F/Rb complexes binding to the E2F-1 promoter.E2F-1 is the prototype of a family of transcription factors playing a central role in the control of cell proliferation and apoptosis. E2F DNA binding activity is down-regulated during cellular differentiation, which is correlated with cell division arrest. We report here that the expression of E2F-1 itself is down-regulated in the developing quail neural retina between embryonic days E8-E10. This event occurs just after the massive arrest of the quail neuroretina cell division (E7-E8). To gain further insight into the regulatory mechanisms monitoring E2F-1 expression in differentiating neurons, we have cloned the quail E2F-1 promoter. In vivo DNA footprintings of this promoter have shown that a number of potential SP-1 and C/EBP response elements are constitutively occupied in the entire quail neuroretina of E5 and E14, whereas the two consensus palindromic E2F binding sites are only protected at E5. This suggests that these E2F elements participate in down-regulation of E2F-1 gene expression during avian neuroretina development. CAT reporter assays have shown that E2F-1 in association with its partner DP-1 transactivates its own promoter, whereas p105Rb inhibits the E2F-1 promoter. Both E2F-1/DP-1 and p105Rh require the presence of the E2F binding sites to mediate their effects. However, experiments performed with deletion mutants of the promoter strongly suggest that other regions located upstream of the E2F binding sites also mediate part of the E2F-1 transactivating effect on its own promoter. Altogether, these results suggest that the down-regulation of E2F-1 gene expression in differentiating neurons could be due, in part, to the E2F/Rb complexes binding to the E2F-1 promoter.

After an initial proliferation phase, neurons of the central nervous system (CNS) of higher eukaryotes remain postmitotic during their entire lifespan. This requires that a very stringent control be exerted on the cell division apparatus, whose molecular mechanisms remain quite elusive. Here we have used quail neuroretina as a model to study the control of cell division in the developing CNS. In vertebrates, embryonic neuroretinal cells (NR cells) stop their proliferation at different times depending on the cell type. Most NR cells in the quail embryo become postmitotic between E7 and E8. To acquire a better understanding of the molecular events leading to quiescence in NR cells, we have analyzed the expression of cdc2 and of two activators of p34(cdc2): cyclin A and cyclin B2 in the developing neuroretina. We report that these three proteins are downregulated between E7 and E9, suggesting that a common mechanism could block their transcription in differentiating neurons. We also report, using an immunohistochemical approach, that p34(cdc2) downregulation is correlated with the appearance of the microtubule-associated protein tau. These results strongly suggest that inhibition of cdc2 gene expression is closely linked to the achievement of terminal differentiation in neurons. However, we also show that postmitotic ganglion cells precursors begin to synthesize the early neuronal differentiation marker beta3-tubulin while p34(cdc2) is still detectable in these cells, suggesting that p34(cdc2) or a closely related kinase could play a role in some "young" postmitotic neurons.After an initial proliferation phase, neurons of the central nervous system (CNS) of higher eukaryotes remain postmitotic during their entire lifespan. This requires that a very stringent control be exerted on the cell division apparatus, whose molecular mechanisms remain quite elusive. Here we have used quail neuroretina as a model to study the control of cell division in the developing CNS. In vertebrates, embryonic neuroretinal cells (NR cells) stop their proliferation at different times depending on the cell type. Most NR cells in the quail embryo become postmitotic between E7 and E8. To acquire a better understanding of the molecular events leading to quiescence in NR cells, we have analyzed the expression of cdc2 and of two activators of p34(cdc2): cyclin A and cyclin B2 in the developing neuroretina. We report that these three proteins are downregulated between E7 and E9, suggesting that a common mechanism could block their transcription in differentiating neurons. We also report, using an immunohistochemical approach, that p34(cdc2) downregulation is correlated with the appearance of the microtubule-associated protein tau. These results strongly suggest that inhibition of cdc2 gene expression is closely linked to the achievement of terminal differentiation in neurons. However, we also show that postmitotic ganglion cells precursors begin to synthesize the early neuronal differentiation marker beta3-tubulin while p34(cdc2) is still detectable in these cells, suggesting that p34(cdc2) or a closely related kinase could play a role in some "young" postmitotic neurons.

International audience; Quail neuroretinal cells (QNR cells) from 7-day-old embryos do not proliferate even in the presence of 8% fetal calf serum. After infection by the Rous sarcoma virus (RSV) they proliferate actively and exhibit a transformed phenotype; this effect is mediated by the oncoprotein pp60v-src. Secondary cultures infected by the thermosensitive strain tsNY68 of RSV are blocked in G0 either by thermal inactivation of pp60v-src at 41.5 degrees C or by serum deprivation at the permissive temperature (36.5 degrees C). Cell division is reinduced either by pp60v-src thermal renaturation or by subsequent serum addition. Our results indicate that v-src and serum control two synergic pathways leading to G0/G1 transition in QNR cells. In order to characterize genes related to the mitogenic and transforming effects of v-src in nerve cells, we have constructed a cDNA library from QNR cells transformed by tsNY68. We report the properties of five molecular clones isolated by differential screening of this library. Unlike immediate-early genes like c-fos, they are induced in mid and late G1. Four of them correspond to unknown mRNAs and the last one codes for nucleolin. This set of v-src-regulated genes is likely to code for functions deficient in terminally differentiated QNR cells and necessary for the progression in G1.Quail neuroretinal cells (QNR cells) from 7-day-old embryos do not proliferate even in the presence of 8% fetal calf serum. After infection by the Rous sarcoma virus (RSV) they proliferate actively and exhibit a transformed phenotype; this effect is mediated by the oncoprotein pp60v-src. Secondary cultures infected by the thermosensitive strain tsNY68 of RSV are blocked in G0 either by thermal inactivation of pp60v-src at 41.5 degrees C or by serum deprivation at the permissive temperature (36.5 degrees C). Cell division is reinduced either by pp60v-src thermal renaturation or by subsequent serum addition. Our results indicate that v-src and serum control two synergic pathways leading to G0/G1 transition in QNR cells. In order to characterize genes related to the mitogenic and transforming effects of v-src in nerve cells, we have constructed a cDNA library from QNR cells transformed by tsNY68. We report the properties of five molecular clones isolated by differential screening of this library. Unlike immediate-early genes like c-fos, they are induced in mid and late G1. Four of them correspond to unknown mRNAs and the last one codes for nucleolin. This set of v-src-regulated genes is likely to code for functions deficient in terminally differentiated QNR cells and necessary for the progression in G1.

International audience; The effects of MDP, a potent inducer of cytokines, were studied in four batches of Wistar Furth rats with established experimental arthritis. Arthritic rats were given a daily sc injection of 10, 100, 200 or 400 micrograms MDP respectively. Muramyl dipeptide increased the severity of clinical events in a dose-dependent manner, with the exception of the 10 micrograms dose which was ineffective. The levels of anti-collagen antibodies were not however significantly enhanced by MDP. Radiological lesions and histological changes were maximal at high dosage regimens. Paradoxically, the acute phase reactive alpha 1 glycoprotein was little affected by MDP treatment.