Differential distribution of poly(A)-containing RNA in the embryonic cells of Oncopeltus fasciatus. Analysis by in situ hybridization with a [³H]poly(U) probe

The regional distribution of poly(A)⁺ RNA was examined in the embryonic cells of the milkweed bug, Oncopeltus fasciatus, by in situ hybridization of histological sections with a [³H]poly(U) probe. As shown by a number of control experiments, this probe interacts specifically with poly(A) sequences preserved in the sections. Using this method, it was shown that labeling of periplasmic and vitellophage nuclei increases markedly early during syncytial blastoderm formation. At this time, label also increases in the vitellophage cytoplasm but not in the cytoplasm surrounding the blastodermal nuclei. Labeling continues to increase in the blastodermal nuclei during cellularization and germ band differentiation without a concomitant accumulation in the blastodermal cell cytoplasm. At the time of germ band invagination, the region of the most intense subcellular labeing shifts from the nucleus to the cytoplasm of the invaginated cells. This shift is not evident in the blastodermal cells which remain at the surface of the egg to become the serosa. In the serosa and the vitellophage energids, labeling then decreases as histogenesis proceeds. Significant labeling of the nuclei and cytoplasm of the invaginated germ band cells continues through germ layer formation. It is concluded that poly(A)⁺ RNA, probably synthesized de novo following oviposition, is subject to differential intracellular distribution in three types of Oncopeltus embryonic cells which may reflect cell-specific patterns of mRNA or poly(A) metabolism.