Identification of a Sperm Nuclear Annulus: A Sperm DNA Anchorl

We report the isolation and characterization of a new nuclear structure from spermatozoa of the golden Syrian hamster which we term the nuclear annulus. The nuclear annul us was located at the implantation fossa, the point at which the tail is joined to the sperm head, inside the nucleus adjacent to the inner nuclear envelope. Extraction of sperm nuclei with 2 M NaC1 and 10 mM dithiothreitol caused the solubilization of the protamines and DNA decondensation. This released the DNA from its structural constraints except that the DNA remained anchored to the nuclear annulus, which survived the extraction procedure. Nuclear aniudi were isolated and examined by scanning electron microscopy. The nuclear annul us was a double-crescent, ring-shaped structure, 2.10 ± 0.16 .un long and 136 ± 0.13 un wide. We believe that the nuclear annulus may play an important role in the organization of sperm DNA.