Three structures associated with the nucleolus in male rat germinal cells: Round body, coiled body, and “nubecula” and general presence of round body at male meiosis

Abstract

In addition to chromosomes and nucleoli, three structures, i.e., round body, coiled body, and nubecula, are encountered in the nucleus during the meiotic prophase in male rats. These structures have been examined by electron microscopy in random and serial sections. The round body is a finely fibrillar, proteinaceous structure closely associated with the granular component of a nucleolus in rat spermatocytes and young spermatids. A similar structure has been observed in man, the monkey Macaca mulatta, the gastropod Achatina fulica, and the insect Locusta migratoria. Together with evidence from the literature, these results support the view that the round body is of general occurrence in the male meiocytes of eukaryotes and may, therefore, play a role in meiosis. The coiled body is a group of electron-dense elements called "coils", which average 35 nm in width, except after mid-pachytene when their size almost doubles. The coils are composed of 2-nm-wide filaments and 8 to 10-nm-wide granules, both of which are ribonucleoprotein. The coiled bodies are interpreted to be groups of "spliceosomes", that is, structures containing heterogeneous RNA and small nuclear RNA. A remarkable feature of the coiled body is its temporary disappearance at early pachytene and its reappearance at late pachytene, possibly due to drastic changes in the turnover rate of its component RNAs. The nubecula is a newly identified nuclear inclusion, composed of weakly staining threads loosely organized into a 560 nm-wide spheroid. It has been observed only in early pachytene nuclei.

Transcription-dependent colocalization of the U1, U2, U4/U6, and U5 snRNPs in coiled bodies

“…Coiled bodies are typically described at the ultrastructural level as oval to spherical inclusions, ranging in size from 0.3-0.9 tim and giving the appearance of bundles of "knotted threads." They also appear to be highly conserved in evolutionary terms, showing a similar appearance in eukaryotes as diverged as plants and mammals (43,57) . While an extensive literature exists describing the appearance and occurrence of coiled bodies, few functional studies have been carried out to address their biological role.…”

The Movement of Coiled Bodies Visualized in Living Plant Cells by the Green Fluorescent Protein

“…This nuclear organelle was later reidentified by electron microscopy and renamed the "coiled body" because of its appearance as loosely packed coiled fibrils (Monneron and Bernhard, 1969). Subsequent studies detected coiled bodies in animal and plant nuclei, showing that it is a conserved structure (Moreno Diaz de la Espina et al, 1980;Seite et al, 1982;Schultz, 1990).…”

“…This nuclear organelle was later reidentified by electron microscopy and renamed the "coiled body" because of its appearance as loosely packed coiled fibrils (Monneron and Bernhard, 1969). Subsequent studies detected coiled bodies in animal and plant nuclei, showing that it is a conserved structure (Moreno Diaz de la Espina et al, 1980;Seite et al, 1982;Schultz, 1990).Coiled bodies have been shown to contain splicing small nuclear ribonucleoproteins (snRNPs) and small nuclear RNAs (snRNAs), a subset of nucleolar components -including fibrillarin, Nopp140, NAP57, and U3 small nucleolar ribonucleoprotein (U3 snoRNP) -and the protein p80 coilin, which has been widely used as a marker for coiled bodies (Lamond and Earnshaw, 1998;Matera, 1998). The function of coiled bodies is still under debate, but several hypotheses have been proposed that are not necessarily mutually exclusive.…”

Convoluted cords, a new nuclear body in spermatocytes and spermatids of the rabbit

“…They are never associated with or included in the nucleoli. This excludes any similarity with the round bodies (Schultz 1990), the nubecula and the coiled bodies. The last mentioned also contain hnRNPs (Fakan et al 1984), which have not been found in the present study.…”

“…They contain heterogeneous ribonucleic acids (hnRNAs), are associated with or are included in the nucleoli and have a diameter of 0.4±1.6 m. (3) The ªnubeculaº (Schultz 1990) have been described as having a diameter of 0.5 m and are compact and faintly stained structures surrounded by a pale halo. They are present in rat primary spermatocytes in stages I±VI of the seminiferous epithelium.…”