Interchromatin granule clusters of the scorpionfly oocytes contain poly(A)⁺ RNA, heterogeneous ribonucleoproteins A/B and mRNA export factor NXF1

Abstract

IGCs (interchromatin granule clusters), or nuclear speckles, are one of the most universal subnuclear organelles of eukaryotic cells. We have used insect oocytes to study the possible association of poly(A)+ RNA and some factors involved in mRNA export with IGCs. Oogenesis of the mecopteran, Panorpa communis, used as a model object, is characterized by a strict cessation of oocyte genome transcription activity towards the end of oocyte growth. Our previous studies on P. communis oocyte nuclei have shown that oocyte IGC counterparts in this species are very unusual, both in morphology and molecular composition, compared with the typical IGCs of mammalian somatic cells traditionally used as a model system. We have now used microinjections of 2'-O-Me(U)₂₂ probes conjugated with the fluorochrome TAMRA to localize poly(A)+ RNA in IGCs. RNA export proteins were also detected by immunofluorescent/confocal and immunogold labelling electron microscopy. We found that poly(A)+ RNA, hnRNPs A/B and NXF1 mRNA export factors are located in IGCs regardless of the transcriptional status of the nucleus. Our data support the idea of IGCs as universal and conserved nuclear domains that serve not only as splicing factor reservoirs, but also take part in mRNA retention and export.

Nuclear structures in Tribolium castaneum oocytes

“…The vast majority of SC35 domains in T. castaneum GVs contain poly(A) + RNA. Using 2′‐ O ‐Me(U) 22 microinjections, some poly(A) + RNA was also demonstrable in oocyte SC35 domains of the yellow mealworm T. molitor (Bogolyubov et al, ), the scorpionfly P. communis (Batalova et al, ) and in IGCs of 2‐cell mouse embryos (Bogolyubova et al, ).…”

“…These particles serve as substrates for posttranscriptional modifications of these RNAs (Dreyfuss et al, 1993). Recently, hnRNPs of the A/B family including the most abundant protein A1 were localised in the SC35 domains of P. communis and T. molitor oocytes (Batalova et al, 2010;Bogolyubov et al, 2012a) and in the IGCs of 2-cell mouse embryos (Bogolyubova et al, 2009). A1 hnRNP is involved in many nuclear functions including mRNA export (He and Smith, 2009).…”

mRNA accumulation in the Cajal bodies of the diplotene larch microsporocyte

“…Previous reports regarding the spatial organization of successive pre-mRNA maturation stages indicate that the main sites of poly(A) RNA and mRNA concentration in the nucleus are dynamic, irregular structures termed speckles (Carter et al 1991, 1993; Wei et al 1999; Molenaar et al 2004; Xie and Pombo 2006; Ishihama et al 2008; Bogolyubova et al 2009; Batalova et al 2010). We have previously demonstrated that in larch, poly(A) RNA localizes in speckles, but this occurred independently from the RNA accumulation in nuclear bodies (Kołowerzo et al 2009).…”

Microscopic Analysis of Nuclear Speckles in a Viviparous Reptile

“…They were described first in mammalian cells in culture and some tissues [4,5] but currently are known as well-established compartments within the nuclei of eukaryotes [6]. They have been described in protists, plants, and invertebrate and vertebrate animals, although with different morphological and ultrastructural patterns as well as different possible functions according to the cell type and biological model in study [7][8][9][10][11][12][13]. Morphologically, speckles are surrounded by a diffuse staining environment [14,15], and their number, morphology, and size vary in relation to gene expression [16,17].…”