EVIDENCE For THE CYTOPLASMIC SYNTHESIS OF NUCLEAR HISTONE DURING SPERMIOGENESIS IN THE GRASSHOPPER CHORTOPHAGA VIRIDIFASCIATA (DE GEER).
Histone synthesis during spermiogenesis in the grasshopper Chortophaga viridifasciata was studied using autoradiographic and cytochemical methods. It was found that meiosis is followed by a cessation of RNA synthesis, an elimination of RNA from the nucleus, and, during the cytoplasmic sloughing accompanying the initial cytoplasmic elongation, a loss of most of the RNA from the cell. The initial phase of cell elongation results in a long spermatid headed by a spherical RNA-less nucleus bounded by a thin RNA-containing layer of cytoplasm. Subsequent nuclear elongation is accompanied by a replacement of the typical histones by others rich in arginine. This replacement is the result of synthesis of new protein. Incorporation of arginine is first seen to occur in the thin cytoplasmic layer surrounding the nucleus. This layer was shown by staining and electron microscopy to contain aggregations of ribosome-like particles. These observations support the conclusion that the histone is synthesized in association with the RNA granules in the cytoplasm, then migrates into the nucleus where it combines with the DNA.
Bloch
D P
DP
Department of Botany, the University of Texas, Austin.
Brack
S D
SD