RNA POLYMERASE II AND PRE-mRNA SPLICING FACTORS IN DIPLOTENE OOCYTE NUCLEI OF
ACHATINA FULICA (MOLLUSCA: GASTROPODA)
I. S. Stepanova,1 D. S. Bogolyubov
Institute of Cytology RAS, St. Petersburg;
1 e-mail: ir@mail.cytspb.rssi.ru
The nuclear distribution of pre-mRNA splicing factors (snRNPs and SR-protein SC35) and unphospho-rylated from of
RNA polymerase II (Pol II) was studied using fluorescent and immunoelectron cytochemistry in diplotene oocytes of
the gastropod Achatina fulica. Association of Pol II and splicing factors with oocyte nuclear structures was
analysed. The antibodies against splicing factors and Pol II were shown to label perichromatin fibrils at the
periphery of condensed chromatin blocks as well as those in interchromatin regions of nucleoplasm. The revealed
character of distribution of snRNPs, SC35 protein, and Pol II, together with the decondensed chromatin and absence
of karyosphere, enable us to suggest that oocyte chromosomes maintain their transcriptional activity at the
diplotene stage of oogenesis. In A. fulica oocytes, sparse nuclear bodies (NBs) of a complex morphological
structure were revealed. These NBs contain snRNPs rather than SC35 protein. NBs are associated with a fibrogranular
material (FGM), which contains SC35 protein. No snRNPs were revealed in this material. Homology of
A. fulica oocyte nuclear structures to Cajal bodies and interchromatin granule clusters is discussed.
Key words: RNA polymerase II, splicing factors, immunoelectron cytochemistry,
mollusca, Achatina fulica
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