Abstract
AbstractAfter X‐ray irradiation, it is possible to obtain follicles and eggs of the gall midge Heteropeza pygmaea lacking the follicular epithelium. These “naked” eggs are able to develop up to the blastoderm stage but remain spherical instead of assuming an elongated shape. Polar plasm and pole cell formation have been studied at the ultrastructural level to investigate the role of the follicular epithelium and of the egg shape in the establishment of egg polarity and in the differentiation of germ line cells. It is shown that the normal egg shape and the follicular epithelium are not needed for the establishment of the anterior‐posterior polarity, as it is manifested by the polar plasm. Moreover, the polar plasm appears at that part of the naked eggs that is at the opposite side of the nurse chamber. Naked eggs are also able to form pole cells in a sequence of events, which strongly resembles that of pole cell formation in normal eggs. These events are described and discussed; they include the changes in the morphology of the polar granules and their association with other organelles during development, the shifting of the polar plasm towards an approaching cleavage nucleus, the cleavage of the first pole cell, and the appearance of pole cell‐specific nuclear lamellae.
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