COMPARATIVE MOTILITY OF X-CHROMOSOME-BEARING AND Y-CHROMOSOME-BEARINGBOVINE SPERM SEPARATED ON THE BASIS OF DNA CONTENT BY FLOW SORTING

A combination of flow cytometric sperm sorting of X and Y chromosome-b earing sperm (X and Y sperm) and computer-assisted sperm analysis (CAS A) for measuring sperm motility allows assessment of motion parameters in the two populations. Bull sperm were separated into X and Y popula tions by flow cytometry following staining with the DNA-binding dye Ho echst 33342. The motion parameters differed de pending on sperm concen tration. Decreasing sperm concentration resulted in higher velocities and straighter trajectories. The concentrations of control (stained-un sorted and unstained-unsorted) and flow-sorted sperm were therefore ad justed to similar numbers (5 x 10(6) sperm per milliliter). Samples of sorted X and Y sperm and control sperm were transferred to prewarmed slides on a heated stage (37 degrees C) and their motion video recorde d for 2 min using a magnification of x100 and a high-resolution camera . The sperm analysis was carried out on a Hobson Sperm Tracker (HST) u sing HST 7 software. The following motion parameters were measured: cu rvilinear, straight-line, and average path velocity; mean angular disp lacement (MAD); beat cross-frequency; amplitude of lateral head displa cement; linearity (LIN); and straightness of path (STR). Sperm movemen t was unaffected by staining with Hoechst 33342, excitation by ultravi olet (UV) light, or 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 in a simple salts solution, Y bull sperm do not swim faster than X sperm but may be distinguished from X sperm on the basis of LIN and STR. (C) 1998 Wiley-Liss, Inc.