[Intranuclear structures containing RNA maturation factors in early vitellogenic oocytes of Rana temporaria].
We have examined the distribution of RNA processing factors in the germinal vesicle (GV) of the common frog Rana temporaria during early vitellogenesis by immunostaining on light- and electronmicroscopic levels and by in situ nucleic acid hybridization. Small nuclear RNPs (snRNP) and factor SC35 involved in pre-mRNA splicing occur in lampbrush chromosome loops and numerous granules 1-3 microns in size. These granules are identical to B snurposomes of Xenopus laevis and Notophtalmus viridescens described earlier (Wu et al., 1991). Some of B snurposomes are attached to homologous loops of lampbrush chromosomes. Immunofluorescent study of Cajal bodies/coiled bodies (CB) showed that sometimes CB have B snurposomes attached to their surface. In this case splicing factor SC35 is found in B snurposomes and B-like inclusions in CB matrix. In CB without attached B snurposomes splicing factor SC35 localizes throughout the whole organelle. Staining of GV spreads with antibodies against nucleolar protein NO38 revealed this protein in CB, nucleoli and micronucleoli. Using in situ nucleic acid hybridization and immunofluorescent staining we have found that on GV spreads from hibernating frogs B snurposomes contact nucleoli. Nucleoli contain snRNP. These data suggest that nucleoli may be storage sites of snRNPs during natural inactivation of RNA synthesis. During winter season in Rana temporaria GV nucleoli become compacted and a number of micronucleoli (less than 2 microns) dramatically increases. Analysis of micronucleoli showed that they contain rRNA, protein NO38, trace amount of U3 small nucleolar RNA and do not contain fibrillarin, involved as U3 in pre-rRNA processing. We suggest that decrease of rRNA synthesis during frog hibernation results in transformation of part of nucleoli in micronucleoli.
Kvasov
I D
ID
Institute of Cytology, Russian Academy of Sciences, St. Petersburg.
Parfenov
V N
VN
Tsvetkov
A G
AG
D000818:Animals; D002466:Cell Nucleolus / Q000648:ultrastructure*; D019084:Fluorescent Antibody Technique, Indirect; D016253:Microscopy, Immunoelectron; D009865:Oocytes / Q000648:ultrastructure*; D012323:RNA Processing, Post-Transcriptional; D011896:Rana temporaria; D014818:Vitellogenesis