Electrophoretic analysis of newly synthesized and stored maternal RNA during oogenesis ofCalliphora erythrocephala...

Ovaries ofC. erythrocephala synthesize large amounts of poly(A)⁺ and poly(A)^- RNA during early and middle stages of oogenesis as shown by labelling with³H-uridine in vivo. After incubation for 1 h, a striking difference in the electrophoretic pattern of newly synthesized labelled poly(A)⁺ RNA and the poly(A)⁺ RNA present in sufficient amounts for optical density measurements (steady state poly(A)⁺ RNA) was observed. During early and mid-oogenesis, in the poly(A)^- RNA fraction, ≧4S predominantly mature rRNA, 5S RNA and tRNA were labelled. These fractions were no longer synthesized during late oogenesis, whereas poly(A)⁺ RNA was labelled continously During oogenesis stage specific differences in the size distribution of newly synthesized and steady state poly(A)⁺ RNA were not obvious. However, different sizes of labelled poly(A)⁺ RNA species were detected in 0-2h old preblastoderm embryos, after injection of³H-uridine into females either 3-4 days (stage 3-4 of oogenesis) or 24 h before oviposition (stage 5-6 of oogenesis). This difference in RNA synthesis was related to the presence of active nurse cell nuclei. The poly(A)⁺ RNA fraction represents about 2-3% of the total RNA in both ovaries and freshly laid eggs as judged by measurements of optical density and radioactivity bound to oligo(dT). The length of poly(A)-segments in ovarian poly(A)⁺ RNA varied from about 30 to 200 nucleotides.