DEVELOPMENT OF THE NUCLEAR STRUCTURE AND METABOLISM DURING OOGENESIS OFPERINEREIS CULTRIFERA(ANNELIDA, POLYCHAETA)

Abstract

An ultrastructural study of the nucleus was carried out, during oogenesis of Perinereis cultrifera, accompanied by an autoradiographic and biochemical study of the syntheses of RNA. The nucleus encloses formations deriving from the dispersal of meiotic chromosomes and a voluminous nucleolus. The latter undergoes morphological development of which each stage is characteristic of a stage of oogenesis. The autoradiographic study shows that the synthesis of RNA of extra-nucleolar origin is highly intense in young oocytes (during the stages of previtellogenesis and vitellogenesis) and that it decreases in older oocytes. The synthesis of RNA of nucleolar origin is very weak during previtellogenesis, increases during vitellogenesis, which is the stage at which it reaches its peak, and then decreases during the stages of the development of cortical alveoli and of maturity. These autoradiographic results are confirmed by a biochemical study which shows that once an oocyte diameter of 80 Jlm is reached (mid-vitellogenesis), the specific radioactivity of 18 and 28 S rRNA and of 4 and 5 S RNA decreases progressively up to the end of oogenesis.

Oogenesis and oocytes

“…Ultrastructural changes in the nucleus during the previtellogenic phase correlate with ooplasmic metabolic events but our knowledge is largely confined to studies of nereidid species (Dhainaut, 1972(Dhainaut, , 1984Bertout et al, 1981). A prominent nucleolus appears during the diplotene stage and assumes a central position as oocyte growth begins (Fig.…”

Structure of the germinal vesicle during oogenesis in leechGlossiphonia heteroclita (Annelida, Hirudinea, Rhynchobdellida)

“…Finally, it is noteworthy that in two polychaetous annelids the synthesis of extranucleolar RNA has been observed. Namely, during oogenesis the fibrillar part of the nucleolus divides into numerous small nucleoli (micronucleoli) which in vitellogenesis migrate toward the nuclear envelope (Andreson and Huebner, 1968;Bertout et al, 1981). Additionally, in Diopatra cuprea and Onuphis sp., infoldings (plications) of the nuclear envelope have been found (Anderson and Huebner, 1968;Eckelbarger, 1992).…”

Ultrastructural cytochemistry of the chromosomes of growing oocytes ofPerinereis cultrifera(Nereidae, Polychaeta, Annelida) after fixation in situ

“…First, dense aggregates were always found close to the chromatin of bivalents, often in tight contact with it; they were never located in nucleoplasmic areas devoid of chromatin. Secondly, NG were shown in a previous autoradiographic study [2], to be actually a site of RNA synthesis, the migration of radioactive RNAs from the nucleolus being ruled out since at this time the nucleolar granular component was not yet labelled.…”

“…Only 'nucleoplasmic granulations' (NG) were described and primarily interpreted as nucleolar material in transfer towards the cytoplasm [1]. However, more recent autoradiographic studies suggested that NG could be a site for non-nucleolar RNA syntheses and consequently belong to chromosomes [2]. Consequently, it appeared essential to reinvestigate the significance of NG and their possible relations with diplotene bivalents.…”