An immunoelectron study of karyosphere and nuclear bodies in oocytes of mealworm beetle, Tenebrio molitor (Coleoptera: Polyphaga)

Abstract

The karyosphere and nuclear bodies (NBs) were studied in Tenebrio molitor oocytes using immunoelectron cytochemistry. During early diplotene (previtellogenic stage), oocyte chromosomes begin to unite in a small nuclear volume forming the karyosphere. In vitellogenic oocyte nuclei, the chromatin undergoes condensation, and the karyosphere acquires a ring-shaped structure. The karyosphere is the only structure containing DNA in the oocyte nucleus. Pre-mRNA splicing factors [small nuclear ribonucleoproteins (snRNPs) and SC35] are not found in the karyosphere itself. In previtellogenic oocyte nuclei, these factors are present in NBs and in a fibrogranular substance surrounding the chromosomes in the early stages of karyosphere formation. At this stage, larger fibrillar NBs contain the non-snRNP splicing factor SC35. Smaller roundish NBs were shown to contain snRNPs. Some NBs with the same morphology contain neither snRNPs nor SC35. In the vitellogenic oocyte, there are fibrogranular NBs containing both snRNPs and SC35 splicing factors, fibrillar NBs containing snRNPs only, and complex NBs containing both. Complex NBs are often connected with the ring-shaped karyosphere. Based on the obtained immunoelectron data, we suggest that T. molitor oocyte NBs containing both snRNPs and the non-snRNP splicing factor SC35 are homologs of the well-characterized B-snurposomes in amphibian germinal vesicles and clusters of interchromatin granules in mammalian oocyte nuclei. Other NBs containing only snRNPs are suggested to represent a special class of insect oocyte snurposomes. The nuclear organelles mentioned seem to play a role as storage domains for pre-mRNA splicing factors during T. molitor oogenesis.

Factors related to RNA polymerase II transcription are localized in interchromatin granule clusters of Panorpa communis oocytes.

“…It should be also noted that P. communis diplotene oocytes used in this study are transcriptionally inert [17] and, in contrast to the active cells, the IGC granules of P. communis oocytes could be the storage sites for the Pol II holoenzyme components disengaged from transcription. The same function of IGCs in inactive insect oocytes was discussed earlier [6,8]. Additionally, our data on tight association of transcriptional coactivators CBP/p300 with granules of IGCs in P. communis oocytes (Fig.…”

“…The nature of some characteristic inclusions observed in oocytes of different insects as the CBs are established now [2][3][4][5] whereas until recently little is known about insect oocyte IGC structure and functions. Insect oocyte IGCs have been described only in a beetle [6,7], the house cricket [8], a fleshfly [9] and some bugs [10]. In our previous study, we showed some features of IGC structure and molecular composition in oocyte nuclei of the scorpionfly, Panorpa communis [11].…”

Ovogenèse et transmission des bactéries symbiotiques chez le charançonSitophilus oryzaeL. (Coleoptera: Curculionoidea)

“…Le nom de « karyosphère » est préféré par Gruzova & Parfenov (1993). En réalité, cette structure est retrouvée dans tous les ovarioles méroïstiques étudiés (Bogolyubov et al 2000). Nous l'appelons ici : caryonucléole.…”

Universal nuclear domains of somatic and germ cells: some lessons from oocyte interchromatin granule cluster and Cajal body structure and molecular composition

“…Unfortunately, we still know very little about this subject. To date, IGC counterparts have been described only in some insects including the mealworm beetle, (37,38) the scorpionfly, (39) the house cricket, (40) some bugs, (41) and a fleshfly; (42) however, other ''granular'' NBs, resembling IGCs but of an unknown nature, have also been described in the oocytes of Drosophila, (43) the tse-tse fly, (44) and the dragonfly. (45) In many cases, insect oocyte IGCs possess peculiarities that make them somewhat different from the ''classic'' IGCs of mammalian somatic cells.…”

“…1). (37)(38)(39)(40)(41)(42) Fibrillar areas may occupy a significant portion of the IGCs in insect oocytes. It is unclear whether these fibrillar zones correspond to the socalled interchromatin granule associated zones (IGAZ) described in mammalian cells, (46) but some immunocytochemical data (39,41) suggest that these two zones constitute different IGC subdomains.…”