Submicroscopic Organization of the Nucleus during Spermiogenesis in the Grasshopper

Recent electron microscope studies of nuclei and chromosomes have shown that a microfibril from 100 to 200 A thick is the basic morphological unit of chromosomes. Chromosome fibrils of this dimension have been reported in the salivary gland chromosomes of Drosophila ~irilis (20, 21), in salivary chromosomes of D. melanogaster (9), in leptotene, pachytene, and metaphase chromosomes of Lilium (13-16), in carp erythrocyte nuclei (22), in the somatic interphase nuclei of Lilium, A1lium, and Tradescantia, in the nuclei of liver, pancreas, and testis tissues of the rat and in plasma cells, monocytes, and lymphocytes of mice (4), and in the staminal hairs of Tradescantia (12). We know that in somatic nuclei the chromosomes contain not only deoxyribonucleic acid (DNA) and histones, but also non-histone protein and ribonucleic acid (RNA) (3). During spermiogenesis, however, profound changes take place in the chemistry of the nucleus. Histones are usually replaced by protamines and non-histone proteins are either greatly reduced or absent (7). Inasmuch as the sperm nucleus still carries genetic material, it would be of interest to know what changes in submicroscopic organization of chromosomes are associated with these modifications in chemical composition. In this preliminary note, we wish to report some observations on nuclear structure during spermiogenesis in several species of grasshoppers.