The analysis of the germ cell cluster formation in Anthonomus pomorum (Coleoptera, Polyphaga, Curculionidae) has revealed that both linear and branched clones of cystocytes occur in the pupa stage. In the branched clones a poorly developed polyfusome is formed and cystocytes with maximally 3 intercellular bridges were found. In the linear clones the polyfusomes are absent. Further divisions of cystocytes produce exclusively linearly arranged cells. Just after metamorphosis (Imago-A stage), the process of the germ cell membrane reduction starts. Only 2 groups of cells retain cell membranes: i.e the most anteriorly localized group of cystocytes and the posteriorly located presumptive oocytes. The former cells divide mitotically during the summer. As a result an anterior-posterior gradient of the syncytialization process arises in the Imago-B stage (females preparing for hibernation). In the sexually mature females (Imago-C) the trophic chamber consists of a huge syncytial area with numerous nurse cell nuclei embedded in a common cytoplasm, and posteriorly located young oocytes surrounded by prefollicular cells. In the light of recent hypothesis concerning the germ cell cluster formation and telotrophy anagenesis in Polyphaga the significance of the presented results is discussed.
In developing ovarioles of Anthonomus pomorum (Coleoptera, Polyphaga, Curculionidae) the trophic chambers (tropharia) are relatively large and consist of clusters (clones) of germ cells and various somatic tissues. Each ovariole is enclosed within an outer epithelial sheath (tunica externa). Throughout the pupal phase, the growth of this sheath is accelerated and precedes the development of the rest of the ovariole. As a result, the epithelial sheath proliferates anteriorly and forms an elongated ?sleeve? that during the later stages of development becomes gradually filled by the growing tropharium. In the early pupal stage, a few terminal filament cells are observed in contact with the anterior end of the tropharium. These cells are separated from the rest of the trophic chamber by a transverse septum, which maintains continuity with the basal lamina. Beneath the basal lamina there is a layer of inner sheath cells, whereas inside the tropharium there are interstitial cells. These two types of cell differ morphologically in a mature ovary but they retain, until the end of the imago-B stage, a similar ultrastructure testifying to their common origin. At the posterior end of the tropharium, from the imago-B stage on, many young oocytes, surrounded by prefollicular cells, are observed. This is the so-called neck region of the tropharium. Extraction with Triton X-100 detergent showed that in a mature trophic chamber there are only individual microtubules arranged along the projections of interstitial cells. This indicates that the cytoskeleton elements (microfilaments and microtubules) participate only to a very limited extent in the spatial organisation of the tropharium in A. pomorum.
In the ovarioles of Liophloeus lentus (Insecta, Coleoptera, Curculionidae) two types of bacteria and parasitic microorganisms belonging to Microsporidia have been found. This study shows that the different microsporidian life stages (meronts, sporonts, sporoblasts and spores) infect the outer ovariole sheath, trophic chambers, follicular cells, late previtellogenic and vitellogenic oocytes and eggs. In trophic chambers the parasites are very abundant and are distributed unevenly, i.e. their large mass occupies the syncytial cytoplasm between the nurse cell nuclei, whereas the neck region of the trophic chamber (which houses young oocytes, prefollicular cells and trophic cords) is almost free of parasites. The developing oocytes and eggs contain a lower number of parasites which are usually distributed in the cortical ooplasm. The gross morphology of the ovaries is similar in infected and non-infected specimens. Similarly, the presence of a parasite seems to not disturb the course of oogensis. The only difference was found in the ultrastructure of mitochondria in young previtellogenic oocytes. In the infected females they are unusual i.e. bigger and spherical with tubullar cristae, whereas in the non-infected insects they are elongated and have lamellar cristae. As oogenesis progresses the unusual mitochondria rapidly change their morphology and become similar to the mitochondria in non-infected females. Taking into account the distribution of parasites within the ovarioles, it is suggested that they infect growing oocytes via outer ovariole sheath and follicular epithelium rather than via trophic cords.
Stereological analysis of the ultrastructure of primordial germ cells (PGCs) and the somatic (ectoderm) cells in two developmental stages of embryos and freshly hatched juveniles of Allacma fusca have shown great differences in mitochondria volume density (vd) between the two types of cells. In younger embryos (migration phase of the PGCs) the vd of mitochondria in the cytoplasm of the PGCs is 74.64% higher than in the ectoderm cells. In older embryos, (PGCs in the gonads) the vd of mitochondria is 123% higher than the corresponding value for the somatic cells cytoplasm. In the juvenile the vd of mitochondria in the ectoderm cells grows twice but is still only 2/3 of the value for the PGCs. On the basis of papers describing a direct relationship between stereological and physiological results the authors conclude that the metabolism of the primordial germ cells during embryonic development of Allacma fusca is much higher than that of the somatic ones. If the above conclusion is correct, the results presented here confirm the ?disposable soma theory? (Kirkwood & Holliday 1979).
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