Flow cytometry of X and Y chromosome-bearing sperm for DNA using an improved preparation method and staining with Hoechst 33342.

A new and improved method of preparing mammalian spermatozoa for high resolution flow cytometric DNA analysis and flow sorting is described. Ejaculated or cryopreserved sperm were briefly sonicated to remove tails and then stained with Hoechst 33342. This simple procedure was found superior to more severe treatments of dimethylsulfoxide washes, fixation in 80% ethanol, and protease digestion of the sperm membranes and tails by papain. Flow cytometric DNA analyses of sperm samples subjected to varying sonication times indicated that X and Y chromosome-bearing sperm populations could be well resolved with as little as 15-sec sonication. In addition, a comparison of sonicated samples stained with four concentrations of bisbenzimide (Hoechst 33342) or 4',6-diamidino-2-phenylindole (DAPI) indicated that 2.5 or 5.0 micrograms/ml of Hoechst was sufficient to resolve the X and Y sperm populations. In order to quantitatively describe the flow cytometric data, several indices (sample quality, orientation and splitting) were developed.