Cyst geometry in the egg chambers of Calliphora erythrocephala Mg. (Diptera: Calliphoridae) ovaries

In the germarium of polytrophic ovarioles of Calliphora erythrocephala (Mg.) fly, four mitotic divisions of cystoblasts give rise to 16-cell germ-line cysts. One cell differentiates into an oocyte, while the remaining 15 cells become nurse cells. Concomitantly actin-rich ring canals are formed at the intercellular junctions. The present study considers a mutual arrangement of the ring canals formed after the second to fourth mitoses relative to the ring canal formed after the first mitotic division in different regions of the germarium and egg chambers. During the cyst formation and its movement to the posterior end of the germarium, the ring canals are displaced relative to one another, thereby giving different branching variants of the cyst. The pattern of cell interconnections becomes stable in germarium region 2b and does not change during the cyst movement along the ovariole despite the cyst polarizes and increases in size.

[Analysis of sex chromosome homologies in representatives of the family Calliphoridae]

The distribution of sequences homologous to the Calliphora erythrocephala Mg. sex chromosome was studied in Protophormia terranovae R-D and Lucilia sp. The chromatin structure was found to be similar in regions containing homologous DNA sequences.

[Intranuclear dynamics of chromosome 6 in nurse cells of Calliphora erythrocephala Mg. (Diptera: Calliphoridae)]

Intranuclear dynamics of chromosome 6 in nurse cell nuclei of Calliphora erythrocephala Mg. (Diptera: Calliphoridae) was studied. The 3D FISH method was used for the first time to study chromosome territories in highly polyploid nuclei whose chromosomes undergo morphological changes. A considerable change in the intranuclear location of chromosome 6 and a morphological alteration of the chromosome territory in the course of chromatin polytenization were revealed.

[Analysis of the spatial organization of the XL chromosome attachment site in nurse cell nuclei of the malaria mosquito Anopheles atroparvus]

The spatial position of the site of XL chromosome attachment to the nuclear envelope of ovarian nurse cells relative to the oocyte has been analyzed in the malaria mosquito Anopheles atroparvus. The XL chromosome attachment sites in the oocyte-nurse cell system of this species have been demonstrated to be orderly arranged, with the attachment sites in two out of three nurse cells in the same layer identically oriented relative to the oocyte.

[Development of ovarioles and nurse cells cytoskeleton in Calliphora erythrocephala Mg. (Diptera; Calliphoridae)]

We have carried out the analysis of ovariole development and morphology in Calliphora erythrocephala Mg. (Diptera: Calliphoridae). It has been shown that several regions can be distinguished in C. erythrocephala germarium. In these regions cyst morphogenesis goes on stage by stage right up to the separation of formed egg chamber. There are fusomes of different degree of branching in germarium. Two egg chambers develop in C. erythrocephala vitellarium. We have researched distribution of actin filaments and ring canals formation in the nurse cells of C. erythrocephala. Diameter of ring canals increases from 1.5 microm in germarium zone to 14.7 microm at 3 and 4 stadies oogenesis. We suggest the scheme that illustrates irregular stretching of actin rollers which are formed during middle and late oogenesis around the ring canals joining proximal, sharply increased in size nurse cells with neighboring nurse cells.

[Visualization of chromosome territories in interphase nuclei of ovarian nurse cells in Calliphora erythrocephala Mg. (Diptera: Calliphoridae)]

Analysis of localization of chromosomes 2, 3, and 6 of Calliphora erythrocephala Mg. in ovarian nurse cell nuclei with different chromatin structure has shown that the regions of DNA probe hybridization reduced with increasing chromatin compaction. Hybridization of DNA probes of chromosomes 3 and 6 to secondary reticular nuclei demonstrated that chromosomes retain their territories in the nuclei when the chromatin acquires a reticular structure. These results suggest regular organization of the chromosomal apparatus at all stages of the endomitotic cycle, including the stage of highly polyploid reticular nuclei. FISH of DNA probe of the chromosome 2 telomeric region to secondary reticular nuclei revealed a peripheral distribution of the signal. Zones of more intensive DNA probe hybridization have been distinguished. These zones probably are the regions of accumulation of telomeric and (or) centromeric chromosome regions.

[Organization and differential staining of chromosomes from the endomitotic nucleus of trophocytes Calliphora erythrocephala (Diptera: Calliphoridae)]

The structure of primary polytene chromosomes and general architecture of nurse cell nuclei was studied in Calliphora erythrocephala using various methods of differential chromosome banding(G-, R-, C-banding; Ag- and DAPI staining), chromospecific DNA probes and fluorescence in situ hybridization. This analysis revealed differential compaction of particular chromosome regions. The localization of material of polytene chromosome 6 is retained after its rearrangement and the formation of the internal reticular structure of the nucleus. Polytene chromosomes of ovarian nurse cells were shown to have blocks of dense compact material; some of them were more intensely stained by AgNO3. The dynamics of the nucleolus formation was traces at all stages of chromosome polytenization in the C. erythrocephala nurse cells.

[Organization of the primary polytene chromosome in the ovaries of 12 species of the "virilis" group of the genus Drosophila (Sophophora)]

Organization of chromosomes was analyzed in ovarian nurse cells in 12 species of the virilis group of Drosophila. A diffuse chromocenter containing a clearly detectable block of heterochromatin was shown to be characteristic of the phylogenetically ancestral species D. virilis and D. kanekoi. Similar organization of chromosomes was observed in two daughter species, D. lummei and D. falvomontana. The chromocenter disappeared either completely or partially in the phylads montana and virilis, respectively. These species exhibited separate chromosomes attached to a nuclear envelope and dispersed within the nucleus. Detected alterations in chromosome architecture confirm evolutionary trends previously revealed in species of the melanogaster subgroup.