Sexing Mammalian Sperm – Where Do We Go from Here?

Abstract

The only commercially viable method of sexing mammalian sperm is to use a flow cytometer to measure sperm DNA content via fluorescence of the DNA-bound fluorophore Hoechst 33342, and then sort sperm into three populations, probably X, probably Y, and undetermined. Millions of insemination doses of sexed sperm are produced annually by this procedure. Although accuracy of sexing usually exceeds 90%, this procedure of sexing one sperm at a time has serious limitations, including cost, sort rates, and damage to sperm resulting in lowered fertility, but not abnormalities in offspring. Suggested areas for research include determining how sperm are damaged and where in the process of fertilization and embryonic development the infertility is manifest. Pre and post sorting procedures are done in approximately hourly batches, and these might be changed to continuous procedures. Numerous genetic, physical, and immunological procedures for sexing millions of sperm in parallel have been proposed, but none appears to be suitable for commercialization at this time due to issues of accuracy, repeatability, damage to sperm, and other problems. However, increasing numbers of reports are appearing concerning improvements in these procedures, and it appears inevitable that one or more of them eventually will prove to be efficacious. In developing such procedures, it is critical to monitor sexing accuracy regularly by rapid and inexpensive procedures such as fluorescence in situ hybridization, quantitative PCR, or sort reanalysis by flow cytometry. Furthermore, monitoring fertility of sexed sperm such as in vitro fertilization should be integral to the development process. Intellectual property issues could be substantive.