Polar granules of Drosophila. IV. Cytochemical studies showing loss of RNA from polar granules during early stages of embryogenesis

Polar granules stain with basic dyes at pH 4.0 in 1 μ plastic sections of mature eggs and of embryos immediately after fertilization. This staining property is removed with hot trichloacetic acid hydrolysis. After the formation of pole cells, polar granules no longer stain at pH 4.0. With the indium trichloride procedure of Watson and Aldridge, polar granules of the mature egg stain with moderate density, and their stainability is removed by cold perchloric acid extraction. Following fertilization, the RNA content of the polar granule rapidly decreases, until, at the blastoderm stage, polar granules do not have more electron density than mitochondria. Both their staining properties and their extractibility with acid indicate that polar granules contain RNA which disappears by the blastoderm stage.