| Abstract: | Sperm nucleoprotein changes during male pronuclear development in fertilized sea urchin (Arbacia punctulata) eggs have been examined utilizing the ammoniacal silver reaction (ASR) at the light and electronic microscopic levels of observation. Previous studies and control preparations indicated that the ASR has an affinity for basic proteins, staining intensely those rich in arginine residues. Differences in the affinity of the paternally derived chromatin to the ASR prior to, during, and following pronuclear development were observed. Relative to the female pronucleus the unincorporated sperm nucleus was densely stained. Upon its entry into the egg the sperm nucleus showed a two-fold increase in staining, indicating an augmentation in the availability of reactive sites already present in the paternally derived chromatin or an accumulation of “new” reactive sites from the egg cytoplasm. With the dispersion of the sperm nucleus there was a progressive decrease in staining intensity of the paternally derived chromatin. Subsequent to pronuclear fusion the paternally derived chromatin, recognized by its relatively dense staining, was seen at one pole of the zygote nucleus. With time there was a gradual regression in the size and staining intensity of the paternally derived chromatin within the zygote nucleus. Changes in reactivity of sperm-derived chromatin are discussed in reference to previous studies of chromatin transitions at fertilization. |
