Nuclear structures in Tribolium castaneum oocytes

Abstract

The first ultrastructural and immunomorphological characteristics of the karyosphere (karyosome) and extrachromosomal nuclear bodies in the red flour beetle, Tribolium castaneum, are presented. The karyosphere forms early in the diplotene stage of meiotic prophase by the gathering of all oocyte chromosomes in a limited nuclear volume. Using the BrUTP assay, T. castaneum oocyte chromosomes united in the karyosphere maintain their transcriptional activity until the end of oocyte growth. Hyperphosphorylated RNA polymerase II and basal transcription factors (TFIID and TFIIH) were detected in the perichromatin region of the karyosphere. The T. castaneum karyosphere has an extrachromosomal capsule that separates chromosomes from the rest of the nucleoplasm. Certain structural proteins (F-actin, lamin B) were found in the capsule. Unexpectedly, the karyosphere capsule in T. castaneum oocytes was found to be enriched in TMG-capped snRNAs, which suggests that the capsule is not only a structural support for the karyosphere, but may be involved in biogenesis of snRNPs. We also identified the counterparts of 'universal' extrachromosomal nuclear domains, Cajal bodies (CBs) and interchromatin granule clusters (IGCs). Nuclear bodies containing IGC marker protein SC35 display some features unusual for typical IGCs. SC35 domains in T. castaneum oocytes are predominantly fibrillar complex bodies that do not contain trimethyl guanosine (TMG)-capped small nuclear (sn) RNAs. Microinjections of 2'-O-methyl (U)22 probes into the oocytes allowed revealing poly(A)+ RNAs in these nuclear domains. Several proteins related to mRNA export (heterogeneous ribonucleoprotein core protein A1, export adapters Y14 and Aly and export receptor NXF1) were also detected there. We believe that unusual SC35 nuclear domains of T. castaneum oocytes are possibly involved in mRNP but not snRNP biogenesis.

The karyosphere capsule inRana temporariaoocytes contains structural and DNA-binding proteins

“…The incomplete cessation of transcription generally characterizes karyospheres with a capsule, such as in the oocytes of the lacewing Chrysopa [33] and the red flour beetle Tribolium [17]. Conversely, karyospheres without a capsule (karyosomes) become transcriptionally inert at an early stage of development [34].…”

“…A high concentration of F-actin in the R. temporaria KC was clearly visible after phalloidin staining (Figure 3). Apart from the frog, F-actin was revealed as a key structural protein of the KC in the oocytes of some insects, including six species of green lacewings [49], the apple blossom weevil [50] and the red flour beetle [17]. Thus, F-actin may be considered as a signature component of the KC, which, in turn, is an evolutionarily conserved structure of the oocyte nucleus.…”

“…In the frog, lamins of all three types were found to be present in both the KC and the NE. Since the presence of lamin B was previously documented for certain ultrastructural elements of the KC in beetle oocytes [17], lamins can be considered as evolutionarily conserved constituents of the KC.…”

“…No filamentous KC appears in this case [15]. Beyond amphibians, annulated ‘pseudomembranes’ have also been described in the KC of mosquitos [16], but not the red flour beetle Tribolium castaneum [17]. In R. temporaria , the autonomous pore complexes are associated with fine fibrils, 7–8 nm in thickness, which presumably originate from the central elements of synaptonemal complexes [12].…”

Characterization of Tribolium castaneum oocyte nuclear structures using microinjection of a fusion nuclear protein mRNA

“…At late previtellogenesis, nucleoplasmic nuclear bodies were positive for Y14‐myc (A), whereas similar domains were devoid of labels in vitellogenic oocytes that were microinjected with Y14–myc mRNA (B). We previously determined that these T. castaneum oocyte nuclear bodies are SC35‐containing domains (Bogolyubov et al, ). Scale bars, 10 µm.…”