ISSN 1990-519X, Cell and Tissue Biology, 2012, Vol. 6, Nos. 5 6, pp. 412–422. © Pleiades Publishing, Ltd., 2012. Original Russian Text © D.S. Bogolyubov, A.M. Kiselyov, S.V. Shabelnikov, V.N. Parfenov, 2012, published in Tsitologiya, 2012, Vol. 54, No. 6, pp. 497–507. 412 Remarkable progress has been made over the last few decades in elucidating the molecular mechanisms of critical stages in gene expression, including tran- scription, pre-mRNA processing, and mRNA export (Erkmann and Kutay, 2004; Zorio and Bentley, 2004; Pandit et al., 2008; Fuda et al., 2009). Molecular interactions underlying RNA polymerase II transcrip- tion and key steps of pre-mRNA processing (5'-end capping, splicing, 3'-end nucleolytic cleavage and polyadenylation) have been examined in detail. Molecular factors playing key roles in these processes and their functions have been identified. According to the current understanding, a highly organized three- dimensional structure of nucleoplasm extrachromo- somal space, in addition to the genome-specific nuclear position qua chromosome area, are of partic- ular importance for coordination and regulation of the multistage process of gene expression (Misteli, 2000; Mao et al., 2011). Abbreviations: hnRNP—heterogeneous nuclear RNP, IGC— interchromatin granule cluster, FGM—fibrogranular material, NXF1—nuclear export factor 1, SC35—spliceosome compo- nent 35. † Deceased. The cell nucleus has about ten types of extrachro- mosomal nuclear domains (compartments, or nuclear bodies), which contain a wide spectrum of molecular factors required for gene expression (Matera, 1999; Mao et al., 2011). The most universal and evolution- arily conservative structures besides nucleoli and Cajal bodies are nuclear “speckles,” which are interchroma- tin granule clusters (IGCs), in terms of electron microscopy (Spector and Lamond, 2011). Transient deposit of pre-mRNA splicing factors— small nuclear (sn)RNP and serine/arginine-rich pro- teins (SR proteins)—is a key function of typical IGCs is. These factors are recruited from IGCs to active genes and back to IGCs after termination of the splic- ing cycle (Huang and Spector, 1996; Misteli et al., 1997). It was demonstrated that the recruiting of pre- mRNA splicing factors into transcription sites and pre-mRNA processing is provided by SR protein interaction with C-terminal domain (CTD) of RNA- polymerase II large subunit (Misteli and Spector, 1999). The movement of SR proteins to the sites of active transcription and splicing, as well as their return to IGCs, is governed by their phosphoryla- tion/dephosphorylation cycles (Misteli et al., 1998). Polyadenylated RNA and mRNA Export Factors in Extrachromosomal Nuclear Domains of Vitellogenic Oocytes in the Yellow Mealworm Tenebrio molitor D. S. Bogolyubov*, A. M. Kiselyov, S. V. Shabelnikov, and V. N. Parfenov † Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russia *e-mail: dmitr@mail.cytspb.rssi.ru Received December 24, 2011 Abstract—The nucleus of vitellogenic oocytes of the yellow mealworm Tenebrio molitor contains a karyo- sphere that consists of condensed chromatin embedded in an extrachromosomal fibrogranular material. Numerous nuclear bodies located freely in the nucleoplasm are also observed. Amongst these bodies, coun- terparts of nuclear speckles (= interchromatin granule clusters (IGCs)) can be identified by the presence of the marker protein SC35. Microinjections of fluorescently tagged 2'-O-Me(U) 22 methyl oligoribonucleotide probes, complementary to poly(A) tails of RNAs, revealed poly(A) + RNA in the vast majority of IGCs. We found that all T. molitor oocyte IGCs contain heterogeneous ribonucleoprotein (hnRNP) core protein A1 localized to IGCs in an RNA-dependent manner. The extrachromosomal material of the karyosphere and some nucleoplasmic IGCs also contain the adapter protein Aly known to provide a link between pre-mRNA splicing and mRNA export. The essential mRNA export factor/receptor NXF1 was colocalized with Aly. In nucleoplasmic IGCs, NXF1 was found to localize in an RNA-dependent manner, whereas it was RNA-inde- pendently located in the extrachromosomal material of the karyosphere. We believe our data provide evidence for the implication of nucleoplasmic IGCs in mRNA biogenesis and retention on the path to nuclear export. Keywords: Tenebrio molitor, oocyte nucleus, nuclear bodies, interchromatin granule clusters, laser scanning confocal microscopy DOI: 10.1134/S1990519X12050045