Micromanipulation and Multiple-Strand Displacement Amplification for Forensic DNA Profiling of Single Sperm Cells

In the clarification of sexual assault cases, forensic DNA profiling of single sperm cells can be desirable if only a few sperm cells are present in intimate swabs analyzed, or if sperm cells from more than one individual are present. However, the DNA content of a single sperm cell is far below the sensitivity limits of current standard forensic methods and thus does not allow for reliable DNA profiling. Here, we describe a protocol for micromanipulation of single sperm cells that is based on using an adhesive-coated tungsten needle to pick individual cells that have been spread on an agarose plate. Forensic DNA typing is thereafter accomplished by subjecting the extracted DNA to multiple strand displacement amplification (MDA) prior to analysis. For MDA, the QIAGEN REPLI-g Single Cell kit is used, and DNA profiles are analyzed using the Promega PowerPlex ESX 17 kit followed by capillary electrophoresis. Using this protocol, over 80% complete haploid DNA profiles can be obtained from the majority of single sperm cells picked.