W. Steven Ward, PhD

Professor and Director

Institute for Biogenesis Research Dept. Anatomy, Biochemistry & Physiology Chief, Research Division
Lakshmi Devi and Devraj Sharma Endowed Chair
Portrait of W. Steven Ward, PhD, Professor and Director IBR, University of Hawaiʻi at Mānoa, IBR,

The function and structure of mammalian sperm chromatin

Description Of Research

Our research is focused on the structure of mammalian sperm chromatin and how this is related to function. The main hypothesis that we have tested is that the sperm cell provided the newly developing embryo with more than just the genetic code in the DNA sequence; it also provides a three dimensional organization of the DNA that provides crucial information as to how to use the father’s genetic code.

DNA is packaged very densely in the sperm nucleus in a manner that is different from any other cell type. Most of the histones are replaced by protamines, and the DNA is crystallized into dense toroids with roughly 50,000 bp of DNA, each. Protamine condensation protects the sperm DNA from damage from external insults, and prevents transcription or DNA replication from occurring. We have shown that one structural feature present in all other somatic cells is also retained in sperm chromatin – the organization of DNA into loop domains attached at their bases to the nuclear matrix.

This organization is crucial to two aspects of sperm chromatin function. Shortly after fertilization, the protamines are removed from the sperm DNA and the chromatin is repackaged with histones. The DNA is then replicated, and we have demonstrated that this DNA synthesis requires the loop domain organization to be intact. On the other hand, spermatozoa have the ability to digest their own DNA through an apoptotic-like process in which the sperm DNA is degraded. This degradation occurs on the nuclear matrix.


Our current research efforts are focused on understanding how sperm chromatin structure is related to the events that occur shortly after fertilization and how the DNA packaging in the sperm cell contributes to embryonic development.

Selected Publications