An efficient novel method for analyzing STR loci from a single sperm captured by laser microdissection

DNA profiling of spermatozoa by laser capture microdissection and low volume-PCR

Genetic profiling of sperm from complex biological mixtures such as sexual assault casework samples requires isolation of a pure sperm population and the ability to analyze low abundant samples. Current standard procedure for sperm isolation includes preferential lysis of epithelial contaminants followed by collection of intact sperm by centrifugation. While effective for samples where sperm are abundant, this method is less effective when samples contain few spermatozoa. Laser capture microdissection (LCM) is a proven method for the isolation of cells biological mixtures, even when found in low abundance. Here, we demonstrate the efficacy of LCM coupled with on-chip low volume PCR (LV-PCR) for the isolation and genotyping of low abundance sperm samples. Our results indicate that this method can obtain complete profiles (13-16 loci) from as few as 15 sperm cells with 80% reproducibility, whereas at least 40 sperm cells are required to profile 13-16 loci by standard 'in-tube' PCR. Further, LCM and LV-PCR of a sexual assault casework sample generated a DNA genotype that was consistent with that of the suspect. This method was unable, however, to analyze a casework sample from a gang rape case in which two or more sperm contributors were in a mixed population. The results indicate that LCM and LV-PCR is sensitive and effective for genotyping sperm from sperm/epithelial cell mixtures when epithelial lysis may be insufficient due to low abundance of sperm; LCM and LV-PCR, however, failed in a casework sample when spermatozoa from multiple donors was present, indicating that further study is necessitated.

Laser capture microdissection in forensic research: a review

In forensic sciences, short tandem repeat (STR) analysis has become the prime tool for DNA-based identification of the donor(s) of biological stains and/or traces. Many traces, however, contain cells and, hence, DNA, from more than a single individual, giving rise to mixed genotypes and the subsequent difficulties in interpreting the results. An even more challenging situation occurs when cells of a victim are much more abundant than the cells of the perpetrator. Therefore, the forensic community seeks to improve cell-separation methods in order to generate single-donor cell populations from a mixed trace in order to facilitate DNA typing and identification. Laser capture microdissection (LCM) offers a valuable tool for precise separation of specific cells. This review summarises all possible forensic applications of LCM, gives an overview of the staining and detection options, including automated detection and retrieval of cells of interest, and reviews the DNA extraction protocols compatible with LCM of cells from forensic samples.