Changes in protamine 1 distribution in human sperm nucleus during in vitro sperm-oocyte interaction: an immunoelectron microscopic study.

Objective: To determine whether the process of sperm nuclear destabilization would begin before sperm-oocyte fusion in humans.

Design: Changes in the distribution of human protamine 1 were investigated in human spermatozoa from the ejaculate, in spermatozoa selected by swim-up or Percoll techniques, and in spermatozoa bound to zona pellucida (ZP) from oocytes that failed to fertilize in an IVF program.

Setting: Center for Infertility and Assisted Reproductive Technology, and university departments.

Patient(s): Fifteen couples undergoing an IVF program.

Intervention(s): Women underwent a similar superovulation induction protocol that consisted of GnRH agonist associated with hMG.

Main Outcome Measure(s): Comparative immunoelectron microscopic study of sperm nucleus labeling with an anti-human protamine 1 specific protamine monoclonal antibody.

Result(s): After selection by swim-up or by Percoll, spermatozoa show a significantly lower nuclear labeling than in the ejaculate. After binding to the ZP, labeling increases, more in spermatozoa selected by swim-up than by Percoll, but, after Percoll selection, labeling in zona-bound spermatozoa is lower than in the ejaculate.

Conclusion(s): In humans sperm binding to the ZP induces differences in the accessibility of the anti-human protamine 1 antibody, which are consistent with structural rearrangements of the DNA-nucleoproteins complex. These modifications must be a prelude to sperm decondensation, protamines replacement by histones, and subsequent reactivation of the sperm genome in the oocyte.