Bernard Knibiehler

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Classical electron-microscopic techniques (enzymic digestion, EDTA regressive staining) allied with autoradiographic studies after [3H]uridine incorporation or after RNA synthesis initiated by an exogeneous RNA polymerase in the presence of tritiated GTP, enabled us to describe the fine structure and activity of the nucleolus in an established Drosophila(More)
We have examined directly the expression of one collagen gene (DCg1) during Drosophila melanogaster embryogenesis by means of in situ hybridization. Transcripts of this gene, which were demonstrated to encode a basement membrane type IV collagen chain, began to accumulate specifically in mesodermal derivatives at stages 12-13 of embryogenesis, and not(More)
In embryonic cell-line derivative KCo of Drosophila melanogaster, the nucleolus, like most nucleoli, contains a small proportion of ribosomal DNA (1-2% of the total nucleolar DNA). The ribosomal DNA is virtually the only active gene set in the nucleolus and is found among long stretches of inactive supercoiled heterochromatic segments. We have demonstrated(More)
In mouse testis, the diploid Sertoli cell displays one large nucleolus flanked symmetrically by two heterochromatic masses. The hybridization in situ with [3H]rRNA confirmed that the ribosomal cistrons are localized with in the central nucleolar mass. At the ultrastructural level this nucleolar mass appears to be reticulated and contains numerous fibrillar(More)
Selective silver staining demonstrated that autosomal bivalents containing transcriptively active nucleolar organizers associated with the sex vesicle during pachytene of mouse spermatocytes. Later in pachytene, the nucleolar organizers covered the portion of the sex vesicle furthest from the attachment to the nuclear envelope. Hybridization in situ(More)
Based on data from developmental RNA profiles and in situ hybridization, we report a direct examination of the expression of one collagen gene (Dcg1) during drosophila melanogaster life cycle. These studies show, for the first time, that the expression of a collagen gene is both differential and tissue-specific during the course of development. Moreover,(More)
During meiotic prophase I the nucleolus of the mouse oocyte assumes a reticulate structure of 'nucleolonema' type. This change coincides with the appearance of several secondary fibrillar centres. The number of these centres at diplotene (97-113), largely exceeds that of nucleolar organizers (4c DNA = 20 NORs). The quantitative analysis of autoradiographs(More)
By means of immunocytochemistry with a battery of specific antibodies, we describe the expression of the collagen IV chain produced by the gene DCg1 during the two phases of Drosophila neurogenesis. DgC1 was not expressed in neuronal tissues as shown by in situ hybridization, but the onset of its expression in cells of mesodermal origin was concomitant with(More)
We report a direct examination of the expression of one collagen gene (DCg1) during Drosophila melanogaster metamorphosis, based on data from in situ hybridization. The transcripts of this gene, thought to encode a basement membrane type IV collagen, are mainly accumulated during ecdysis in wandering haemocytes. Our results demonstrate that haemocytes(More)