Fusion of Drosophila oocytes with specified germline sister cells

Abstract

In many animals, oocytes develop together with sister germline cells that pass products to the developing oocyte. In Drosophila, fifteen sister germline (nurse) cells in each egg chamber are known to apoptose by stage 12-13, but we discovered that two specific nurse cells that are juxtaposed to the oocyte are eliminated precociously at stage 10B. These nurse cells fuse with the oocyte and their nuclei extrude through an opening that forms in the oocyte. These nuclei extinguish in the ooplasm, and at stage 11, egg chambers have thirteen nucleated nurse cells and the plasma membrane of the oocyte is mostly restored. In infrequent egg chambers in which nurse cells are not eliminated, oocytes do not develop normally and are not fertilized. Precocious elimination is common to other Drosophila species. We conclude that nurse cells are distinguished by position and identity, and that nurse cell dissolution proceeds in two stages.