Dynamics of the spatial orientation of the pericentromeric heterochromatin regions in the polytene chromosomes of ovarian nurse cells in the Drosophila melanogaster (Diptera: Drosophilidae) oogenesis

The spatial organization of polytene chromosomes and the association of their pericentromeric regions in the Drosophila melanogaster nurse cells during oogenesis have been examined by 3D-immunofluorescence microscopy. All nurse cell chromosomes are shown to contact the nuclear membrane with their pericentromeric regions, and the X chromosome additionally with its telomeric region. Three morphological types of the associations of the nurse cell chromosome pericentromeric regions in the nuclear space are observed: (1) the pericentromeric regions of chromosomes 2, 3, and 4 contact the nuclear membrane at one pole of the nucleus, while the pericentromeric region of the X chromosome does so at the other pole (morphotype I); (2) the pericentromeric regions of chromosomes X, 2, and 3 are separated from each other in the nuclear space and contact the nuclear membrane (morphotype II); and (3) the pericentromeric region of chromosome 2 contacts the nuclear membrane at one pole of the nucleus, while the pericentromeric regions of chromosomes X, 3, and 4 contact the membrane at the other pole (morphotype III). The author, therefore, proposes that the nurse cell nuclei with morphotype I are prevalent at the early stages of oogenesis, while the nurse cell nuclei with morphotype III are most abundant at the late stages. The dynamics of associations of the pericentromeric chromosome regions in the nuclear space of D. melanogaster ovarian nurse cells in the oogenesis demonstrated that there may be some functional relationship between the 3-D organization of the nurse cell chromosomes and the organization of the nucleolus.