Organization and possible functions of microtubule cytoskeleton in hymenopteran nurse cells.

The results of systematic cytochemical and EM studies on the distribution of actin filaments and microtubules in hymenopteran nurse cells are presented. We demonstrate that each nurse cell nucleus is surrounded by a thick three-dimensional cage of microtubules that is engaged in maintaining the position of the nuclei in the cell centers during the flow of the cytoplasm from nurse cells into the oocyte. Hence, the cages represent functional counterparts of actin bundles described in the Drosophila nurse cells. Furthermore, our data suggest that a subset of the microtubules is involved in transferring nuage aggregates from the vicinity of the nucleus towards the nurse cell periphery and the nearest intercellular bridge. A conclusion is reached that despite similar polytrophic organization of the ovaries in both hymenopterans and dipterans, the physiology of their nurse cell-oocyte syncytia appears distinctly different.