RNA synthesis during male meiosis and spermiogenesis

Summary

• 1. Using ³H-uridine, the course of RNA synthesis has been followed autoradiographically during all stages of male meiosis and spermiogenesis in the locusts Schistocerca gregaria and Cyrtacanthacris tartarica and the grasshopper Chorthippus brunneus. Using ³H-thymidine, premeiotic DNA synthesis was followed in Cyrtacanthacris tartarica.

• 2. RNA synthesis is actively carried out by all autosomes throughout first meiotic prophase, up to and including diakinesis, and at second prophase. No RNA synthesis occurs at the contracted stages of first or second metaphase or first or second anaphase.

• 3. RNA is again synthesized by young spermatids, but such synthesis ceases by the time that differentiation begins. No label was detected in the nuclei of differentiating spermatids, even after 8 hours' incubation with ³H-uridine.

• 4. Morphological and functional comparisons suggest that orthopteran prophase chromosomes at male meiosis, and probably all prophase chromosomes, are lampbrush in nature, though to varying degrees.

• 5. The X univalent, allocyclic in its appearance and staining properties, is apparently completely inactive throughout the whole of meiosis. No RNA or DNA precursor could be successfully demonstrated to be incorporated by the X at any stage of male meiosis.

• 6. Nucleoli are present at interphase and early prophase but are usually absent during later prophase stages in this material. They do not label heavily in advance of, or at the same time as, the commencement of the labelling of the rest of the chromatin: they only accumulate greater densities of label after several hours' incubation with the labelled precursor.

• 7. No independent cytoplasmic synthesis of RNA could be detected after up to 2 hours' in vitro incubation in labelled saline at 30° C, though nuclei are heavily labelled after only 1/2 hour. It is some 2–4 hours before nuclear synthesized RNA appears to pass to the cytoplasm in detectable amounts.