OOGENESIS IN DROSOPHILA VIRILIS. I. INTERACTIONS BETWEEN THE RING CANAL RIMS AND THE NUCLEUS OF THE OOCYTE

¹ Department of Biological Sciences, Northwestern University, Evanston, Illinois 60201

In females of Drosophila virilis, germ cells, characterized by conventional division, differentiate into "cystocytes" that engage in a specific number of mitoses, each followed by incomplete cleavage. The result is a cluster of 16 cells joined by canals. The canal rims are made up of overlapping leaves similar to those already described for Habrobracon juglandis. The virilis canal rims become coated with protein microfibrils. Masses of these fibrils detach from the rims and are carried in a stream of cytoplasm to the oocyte. Clusters of microfibrils adhere to the oocyte nucleus which eventually develops a coating of amorphous material 1 µ thick. The nuclei of the 15 sister nurse cells never develop such a coating. We suggest that the nuclear coating prevents the transfer of large molecules to the oocyte nucleoplasm and so insulates oocyte chromosomes from the influence of those compounds that stimulate transcription in the sister nurse cells. Centrioles and asters take part in cystocyte divisions, but are absent from the meiotic division figures. We conclude that centrioles function to generate asters. These in turn facilitate the attachment to localized regions of the plasmalemma of contractile microfibrils that enable furrowing to take place. Less conspicuous "microtubule-organizing centers" organize the spindle which functions to distribute the chromosomes during mitosis.

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