The karyosphere capsule in Tribolium castaneum oocytes

The structure and composition of the karyosphere (karyosome) capsule of the laboratory insect, Tribolium castaneum , were studied with the use of electron and immunoelectron microscopy. Eight stages that characterized the period of oocyte growth have been established basing on the study of nuclear structure dynamics. At the diplotene stage, T. castaneum oocyte chromosomes are being united early to form a compact karyosphere; however, prominent chromatin condensation does not occur at the same time. The process of karyosphere formation is accompanied by the development of a spacious extrachromosomal capsule surrounding chromatin. The capsule consists of a fibrous material of different morphological types. The most prominent molecular components of T. castaneum karyosphere capsule are represented by the proteins of nuclear matrix, including F-actin and lamin B. Apart from the structural proteins, immunocytochemical approach allowed revealing Sm proteins of small nuclear (sn) RNPs and “mature” snRNAs with 2,2,7-trimetyl guanosine (TMG) cap at the 5’-end of their molecules. These data may serve as a base for further broadening of the conception about the functions of the karyosphere capsule as a specialized oocyte nuclear domain. We believe that T. castaneum karyosphere capsule plays not only a structural role, but may be involved directly in the processes related to gene expression.