Polar granules of Drosophila. III. The continuity of polar granules during the life cycle of Drosophila

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Abstract
Polar granules of Drosophila embryos fragment into fibrous bodies which become associated with the nuclear envelope of pole cells prior to the formation of the embryonic gonad. Similar fibrous structures are found attached to the outer nuclear membrane of primordial germ cells and oogonia throughout the life cycle of the fly. These structures have not been found in any other cell type except the germ cell of the testis. During oogenesis, the oocyte nucleus loses the fibrous bodies associated with the nuclear membrane, but the 15 sister nurse cells retain these structures until the end of vitellogenesis. At this time the cytoplasm and fibrous bodies of the nurse cells are contributed to the ooplasm. Occasionally, polar granules are found in previtellogenic stages of oogenesis, but they only accumulate at the posterior tip of the egg during the latter portion of vitellogenesis. After polar granules have formed, they attach to mitochondria in three species studies, but fail to form this association in D. hydei. Fibrous structures in the egg, believed to be the fibrous bodies attached to the nuclear envelope of nurse cells, are found throughout the mature egg, and have the same species‐specific property of associating or not with mitochondria as was found for polar granules. These fibrous bodies are no longer found following fertilization. A possible role of these fibrous bodies in the egg is discussed.
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