[Autoradiographic Studies on RNA and Protein Synthesis in the Early Embryogenesis ofMusca domestica]

Inhibition by ultraviolet light of pole cell formation in Smittia sp (Chironomidae, Diptera): action spectrum and photoreversibility

The formation of pole cells (primordial germ cells) in Smittia sp can be inhibited by ultraviolet (uv) irradiation without causing significant mortality. Until 70 min after egg deposition, pole cells are suppressed by low uv doses applied to the posterior pole region. Microbeam irradiation of a target area including the oosome inhibits pole cell formation; this is not observed after irradiation of other target areas. The action spectrum for uv inhibition of pole cells shows a distinct peak at 260 nm; its shape suggests that a nucleic acid-protein complex acts as an effective target. Independent evidence for the involvement of a nucleic acid moiety is derived from the fact that uv inhibition of pole cell formation is photoreversible. The results are discussed in the context of pole cell determination by localized cytoplasmic components.

Effects of RNA inhibitors on the development of Drosophila embryos permeabilized by a new technique

The molecular analysis of Drosophila embryogenesis has been hindered by the impermeable nature of the vitelline membrane, which has made it difficult to introduce exogenous substances into the developing embryo. We have developed a modification of the permeabilization technique of Limbourg and Zalokar ('73) in which octane is used to permeabilize the vitelline membrane and dimethylsulfoxide is used to facilitate the transport of exogenous substance across the cell membranes. The procedure is highly effective (ca. 95%) and is consistent with a high frequency of normal development. We have used this technique to analyze the effect in vivo of four inhibitors of RNA synthesis (alpha-amanitin, actinomycin-D, rifampin, and rifamycin SV) on the embryogenesis of Drosophila. We have found that there are characteristic stage-specific alterations in the sensitivity of the embryo to these inhibitors which is reflected both by changes in the ID50 dosages and by changes in the developmental abnormalities caused by the drugs. Embryos aged 2-12 hours old undergo a developmental arrest within 30 minutes after application of the inhibitors. Embryos older than 12 hours are able to develop for 140+ minutes after treatment before arresting. The effects of these drugs are consistent with the idea that there exists a definite sequential program of gene activity that is necessary to the normal embryonic development of Drosophila.

[RNA-Synthesis in telotrophic meroistic ovarioles of dysdercus intermedius DIST. (heteroptera, pyrrhoc.)]

RNA in insect ovaries was investigated by polyacrylamide gel electrophoresis to study site of synthesis, transportation and incorporation in mature eggs. Telotrophic-meroistic ovarioles ofDysdercus intermedius were selected for this work since they could be dissected in distinct portions: the apical one with polyploid nurse cells and the vitellarium with oocytes covered by a follicular epithelium. RNA was labeled by injecting radioactive precursors or incubating isolated ovarioles in vitro.In nurse cells labeled rRNA, tRNA and non-ribosomal RNA were found and evidence was presented for the processing of a 39s rRNA precursor molecule in 2 steps (36s and 32s) into 28s rRNA while the 18s rRNA was directly derived from the 36s molecule. A low concentration (0.5 Μg/ml) of α-Amanitin inhibited synthesis of non-ribosomal RNA thereby revealing a more distinct processing pattern for rRNA, while a high concentration (5 Μg/ml) blocked processing at the 36s molecule and led to its accumulation. Appropriate concentrations of Actinomycin D inhibited rRNA synthesis while distinct peaks of non-ribosomal RNA became apparent.RNA synthesized in the follicular cells was similar to the RNA made in the nurse cells only in the high molecular weight RNA. Some material, tentatively named "nucleotide fraction", with a mobility higher than tRNA was detected and could be localized in yolk granules. It was separable from RNA by chromatography on Sephadex G 100 and had an absorption maximum at 255 run. The "nucleotide fraction" could be rapidly labeled. It seemed to be utilized in RNA synthesis during embryogenesis. Mature eggs contained a relatively high amount of the "nucleotide fraction". If a single injection with precursor was done 4 days before analysing the RNA of mature eggs most of the label was found in the "nucleotide fraction". Eggs collected 5-8 days after injection contained only high molecular labeled RNA. This observation correlated well with the timing of egg maturation. It takes 4 days for a group of oocytes to reach the distal part of the vitellarium where yolk production and maturation go on for another 4 days. It is apparent, therefore, that the follicular epithelium contributes the "nucleotide fraction" to the oocyte, while most of the other RNA, including a stable polydisperse class of RNA, is made in the nurse cells and is transported into the oocyte.