Nucleolar structure and synthetic activity during meiotic prophase and spermiogenesis in the rat

Abstract

The ultrastructure of nucleoli was examined in developing rat spermatocytes and spermatids, with the help of serial sections. In addition, the radioautographic reaction of nucleoli as examined in rats sacrificed 1 hr after intratesticular injection of 3H(5')-uridine and taken as an index of the rate of synthesis of ribosomal RNA (rRNA). Primary spermatocytes from preleptotene to zygotene have small nucleoli typically composed of fibrillar centers, a fibrillar component, and a granular component, within which are narrow interstitial spaces. During early and mid-pachytene, nucleoli enlarge to about nine times their initial size, with the fibrillar and granular components forming an extensive network of cords--a nucleolonema--within which are wide interstitial spaces. Meanwhile, there appear structures identical to the granular component but distinct from nucleoli; they are referred to as extranucleolar granular elements. Finally, from late pachytene to the first maturation division, nucleoli undergo condensation, as shown by contraction of fibrillar centers into small clumps, while fibrillar and granular components condense and segregate from each other, with a gradual decrease in interstitial spaces. In secondary spermatocytes, nucleoli are compact and rather small, while in young spermatids they are also compact and even smaller. Nucleoli disappear in elongating spermatids. In 3H-uridine radioautographs, nucleolar label is weak in young primary spermatocytes, increases progressively during early pachytene, is strong by the end of mid pachytene, but gradually decreases during late pachytene up to the first maturation division. In secondary spermatocytes and spermatids, there is no significant nucleolar label. In conclusion, rRNA synthesis by nucleoli is low in young spermatocytes. During pachytene, while nucleoli enlarge and form a lacy nucleolonema, rRNA synthesis increases gradually to a high level by the end of mid pachytene. However, during the condensation and segregation of nucleolar components occurring from late pachytene onward, the synthesis gradually decreases and disappears. The small, compact spermatids arising from the second maturation division do not synthesize rRNA.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 2: Changes in spermatid organelles associated with development of spermatozoa

“…The nubecula is composed of loosely organized threads organized into a 560-nm spheroid ). An ultrastructure study of nucleoli in rat spermatocytes and spermatids was reported by Schultz and Leblond (1990). During early and mid pachytene, nucleoli enlarge nine times their initial size and then undergo condensation in late pachytene spermatocytes.…”

The Nucleolus in the Mouse Oocyte is Required for the Early Step of Both Female and Male Pronucleus Organization

“…Apparently, its nucleolus no longer contains DNA at this point and shows a highly compacted, fibrillar morphology [2,3]. As the nucleolus is eliminated during spermiogenesis [4][5][6], the spermatozoa do not have nucleoli. After fertilization, this maternally derived, transcriptionally inactive fibrillar nucleolus appears in both male and female pronuclei and in the embryonic nuclei of each interphase until the 4-or 8-cell stage; that is, it is present until the time at which zygotic RNA polymerase I activity is fully established [7].…”

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

“…After embedding in Epon, random and serial sections were prepared as indicated in the accompanying article (Schultz and Leblond, 1990). 7.4 were also obtained (Schultz and Leblond, 1990). In addition, a histochemical study of the coiled body was carried out, using phosphotungstic acid for the detection of protein by the method of Silverman and Glick (1969), and using ribonuclease-bound gold for the detection of RNA by the method of Bendayan (1981a,b).…”

“…After embedding in Epon, random and serial sections were prepared as indicated in the accompanying article (Schultz and Leblond, 1990). 7.4 were also obtained (Schultz and Leblond, 1990).…”