Nucleolar organizers in human oocytes at meiotic prophase I, studied by the silver-NOR method and electron microscopy

Abstract

Use of the silver-NOR method to study the nucleolar organizers in human oocytes demonstrates that topographic and quantitative variations occur during meiotic prophase. In the oogonia nucleolus the nucleolar organizers are dispersed, whereas beginning at leptotene and throughout the remaining stages of meiotic prophase they occupy a marginal position in the nucleolus. At leptotene, a modal number of seven nucleolar organizers can be observed, whereas this number falls to 2.5 at pachytene and rises to ten at diplotene, thus showing that there is intense rRNA synthesis during the latter stage of meiosis. During pachytene, one end of the bivalents containing the ribosomal cistrons is always associated with the Ag-positive zone of the nucleolus. Observation of pachytene in the electron microscope shows that the secondary constriction region of D and G bivalents is constantly associated with the fibrillar center of the nucleolus. Comparison of these two methods of investigation reveals that the silver-stained regions of the nucleolus correspond to the fibrillar centers. The latter are surrounded by a layer of electron-dense fibrils corresponding to the zone of rDNA transcription. This electron-dense layer is absent during pachytene when the nucleolus displays spontaneous segregation of its components; this absence is related to temporary arrest of rDNA transcription. The affinity of the fibrillar centers for silver-NOR staining confirms that these structures contain ribosomal cistrons. During the diplotene stage, numerous micronucleoli are formed outside the nucleolar organizers of D and G chromosomes. Most of these micronucleoli present an Ag-positive granule on one of their margins, thus indicating that they contain an actively transcribed sequence of rDNA. This observation confirms the existence of amplification of ribosomal genes in the human oocyte.

Cyclic AMP in oocytes controls meiotic prophase I and primordial folliculogenesis in the perinatal mouse ovary

“…1B) (Beaumont and Mandl, 1962;Peters et al, 1997;Prieto et al, 2004). The dictyate stage was identified by the presence of two to four clearly visible nucleoli and chromosomes that were decondensed and diffuse (Bakken and McClanahan, 1978;Hartung et al, 1979). At 15.5 dpc, the majority of oocytes were in the zygotene stage of meiosis (Fig.…”

“…Combined staining for SYCP1 and SYCP3 was used to determine whether SYCP1 disassembly occurred. The stages of meiotic prophase I were evaluated based on the appearance of axial elements according to previous studies (Hartung et al, 1979;Prieto et al, 2004). In total, 300 oocytes from two ovaries were counted on each slide, and repeated for three animals.…”

Association of ribosomal genes in the fibrillar center of the nucleolus: a factor influencing translocation and nondisjunction in the human meiotic oocyte.

“…Aside from the ribosomal genes, one of the major components of the fibrillar center is an argyrophilic protein (16,(30)(31)(32).…”

Modifications ultrastructurales des cellules germinales femelles au cours de la prophase méiotique chez le rat : étude particulière des membranes après cryofracture

“…Le complexe synaptinémai a également fait l'objet de nombreuses descriptions ultrastructurales au cours des stades leptotène, zygotène et pachytène (Moens, 1969(Moens, , 1973Stockert et al, 1970 ;Comings et Okada, 1971 ;Esponda et Gimenez-Martin, 1972 ;Schleiermacher et Schmidt, 1973 ;Stack, 1973 ;Chevaillier, 1974 ;Rasmussen, 1976 ;Von Wettstein, 1977 Franchi, 1972 ;Bruslé, 1972 ; (Sotelo, 1959 ;Franchi et Mandl, 1962), ni chez la souris (Tsuda, 1965) Schuchner, 1975 ;chat : Morato, 1965 ;champignons : Stockert et al, 1970 ;plantes : La Cour, 1975 ;souris et cailie : Mirre et Stahl, 1976homme : Très, 1975 ;Stahl et al, 1978Stahl et al, , 1980Hartung et al, 1979 ;Mirre et al, 1980 (Curgy, 1972 ;André, 1962 ;De Martino et al, 1979). Les quelques études des mitochondries réalisées chez la femelle (lapin : Anderson, 1968 ;Anderson et al, 1970) Connell, 1975Connell, , 1976Connell, , 1978rat : Nagano, 1980) …”