Submitted to: Journal of Human Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 23, 1998
Publication Date: N/A
Interpretive Summary: The necessity for active and progressive sperm motility for fertilization of eggs in most mammals is well established. Over the past twenty years it has been speculated and also proposed that there is a difference in the swimming speed of X and Y spermatozoa. Some authors have proposed that this perceived faster sperm motility of Y chromosome bearing sperm is suitable for differential separation of X and Y within an Albumin column. In this study we sought to confirm or deny such claims and determine whether or not work done along these lines has merit for our own work in sexing sperm. We found that there was not evidence for a faster swimming speed for bull sperm that carried the Y chromosome. These results lay to rest the notion that Y sperm swim faster than X sperm. Scientists will use these results to establish the merits of various protocols for separation of X and Y sperm.
A combination of flow cytometric sperm sorting of X- and Y- chromosome bearing sperm (X and Y sperm) and computer assisted sperm analysis (CASA) for measuring sperm motility allows assessment of movement parameters in the two populations. Bull sperm were separated into X and Y populations by flow cytometry following staining with the DNA binding dye Hoechst 33342. The motion parameters differed depending on sperm concentration. Decreasing sperm concentration resulted in higher velocity and straight trajectory. The concentrations of control (stained-unsorted and unstained- unsorted) and flow sorted sperm were therefore adjusted to similar numbers (5 X 1,000,000 sperm/ml). Samples of sorted X and Y sperm and control sperm were transferred to pre-warmed slides and their motility video recorded for 2 min on a heated stage (37C) using a total magnification of 100X and a high resolution camera. The sperm analysis was carried out on a aHobson Sperm Tracker (HST) using HST 7 software. The following motion parameters were measured: curvilinear (VCL), straightline (VSL), average path velocity (VAP), mean angular displacement (MAD), beat cross frequency (BCF), amplitude of lateral head displacement (ALH), linearity (LIN) and straightness of path (STR). Sperm movement was not affected by staining with Hoechst 33342, excitation by UV light or by the physical process of cell sorting. Significant differences were seen between X and Y sperm for MAD, LIN and STR. No difference was observed for the other parameters. The results indicate that Y bull sperm do not swim faster than X sperm but may be distinguished from X sperm on the basis of LIN and STR.