Cajal bodies and interchromatin granule clusters in cricket oocytes: Composition, dynamics and interactions

Abstract

The organization and molecular composition of complicated Cajal bodies (CBs) and interchromatin granule clusters (IGCs) in oocytes of the house cricket, Acheta domesticus, were studied using immunofluorescent/confocal and Immunogold labeling/electron microscopy. In A. domesticus oocytes, the CB consists of the fibrillar matrix and a central cavity containing a predominantly granular body with insertions of tightly packed fibrillar material. The latter structure was identified as an "internal" IGC, since it is enriched with the SC35 protein, a marker for IGCs. The IGCs located outside the CB were also identified. Microinjections of the fluorescein-tagged U7 snRNA into the ooplasm showed the targeting of the U7 to the matrix of the CB. Some other essential CB components (coilin, snRNPs, fibrillarin) were found to be colocalized in the matrix of the CB. Neither confocal nor Immunogold microscopy revealed significant amounts of RNA polymerase II (pol II) in the CB of A. domesticus oocytes. The splicing factor SC35 was detected in the matrix of the CB. In oocytes treated with DRB, the amount of IGCs in the nucleoplasm increased significantly, granular and fibrillar components of IGCs were segregated, and the fibrillar areas accumulated pol II. Additionally, IG-like granules were shown to display on the surface of the CB probably due to a shifting from the internal IGC. We believe that in A. domesticus oocytes, CBs are involved in nuclear distribution of splicing factors, but their role in pol II transport is less significant. We also suggest that the formation of complicated CBs is a result of interconnection between two different nuclear domains, CBs and IGCs.

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].…”

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.…”

“…(77) The transcription coactivators CBP/p300 and the basal transcription factor TBP have also been revealed in oocyte CBs from the house cricket. (40) The essential splicing factor SC35 and other SR proteins have not been found in mammalian CBs. (5) However, we have repeatedly debated their presence, together with that of snRNPs, in oocyte CBs from various insects.…”

“…Frequently they are fibrillar in appearance, but they can also be fibrogranular or even granular. (38)(39)(40)54,55) Within a given species, several types of oocyte CBs can be observed in the same cell. For example, oocyte nuclei from the scorpionfly, Panorpa communis, contain a single large body resembling the oocyte CB of some other insects, including Drosophila, together with numerous small NBs.…”