Polar plasm and pole cell formation in an insect egg developing with or without follicular epithelium: An ultrastructural study

Abstract

After 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 a n approaching cleavage nucleus, the cleavage of the first pole cell, and the appearance of pole cell-specific nuclear lamellae.

From egg to pole cells: Ultrastructural aspects of early cleavage and germ cell determination in insects

“…Pole cells and pole cell formation have been studied ultrastructurally in several species of Drosophila (for review see Mahowald et al, 1979b;Swansson and Poodry, 1980), Chironomus dorsalis (Okada, 19671, Wachtliella persicariae (Wolf, 1967), Miastor spec. (Mahowald, 1975, Heteropeza pygmaea (Junquera, 1983;Meats and Tucker, 1976), the kelp fly, Coelopa frigida (Schwalm et al, 1971;Schwalm and Bender, 19731, the moth Pectinophora gossypiella (Berg and Gassner, 1978), Smittia spec. (Zissler, 1987;Zissler and Sander, 1982), Chironomus anthracinus (Zissler and Sander, 1982) and Nasonia (syn.…”

“…Moreover, these studies have been frequently restricted to certain selected egg regions (for review see Zissler and Sander, 1982). Attempts at analyzing the entire cytoarchitecture of the newly laid egg and the early developmental stages (i.e., cleavage to early blastoderm) by TEM have been made so far in certain species of the fruitfly, Drosophila (Engstrom et al, 1982;Fullilove and Jacobson, 1971;Fullilove et al, 1978;Hay et al, 1988a;Kobayashi and Okada, 1989;Mahowald, 1962Mahowald, , 1963aMahowald, ,b, 1968Mahowald, , 1971aMahowald et al, 1976Mahowald et al, , 1979aMahowald et al, ,b, 1981Mahowald et al, , 1983Okada, 1986;Okada and Kobayashi, 1987;Okada and Waddington, 1959;Sanders, 1975;Swanson and Poodry, 1980;Ueda and Okada, 19821, in the cecidomyiide gall midge, Heteropeza pygmaea (Fux, 1975;Junquera, 1983Junquera, , 1985Kaiser and Went, 1987;Meats and Tucker, 1976), in the chironomid midge, Smittia spec. (Zissler, 1987;Zissler and Sander, 1973, 1977 and in the domesticated silkmoth, Bombyx mori (Miya, 1978(Miya, , 1984(Miya, , 1985Takesue, 1985;Takesue and Keino, 1982;Takesue et al, 1985).…”