Hair root sonication washing impact on nuclei counts

Area of Science:

• Forensic Science
• Molecular Biology
• Genetics

Background:

• Sonication washing is used in DNA extraction protocols for hair samples.
• This step was previously considered necessary for both mitochondrial (mt) and nuclear (nu) DNA analyses.

Purpose of the Study:

• To assess the impact of sonication washing on nuclei persistence in hair roots.
• To determine if sonication affects the number of nuclei available for DNA extraction.

Main Methods:

• Scalp hair roots were stained with 4', 6-diamidino-2-phenylindole (DAPI).
• Visible nuclei were counted in both unwashed and sonication-washed hair roots.
• Hair roots with varying initial nuclei counts (<50 and >100) were analyzed.

Main Results:

• Sonication washing may reduce the number of nuclei in hair roots, particularly those with fewer initial nuclei.
• Challenges in nuclei counting included hair root orientation, morphology, and tissue folding.
• A reduction in nuclei could impact DNA extraction yield and short tandem repeat (STR) typing.

Conclusions:

• Sonication washing might deplete nuclei essential for DNA extraction and STR typing.
• Laboratories performing only nuclear DNA analysis can opt for gentler washing methods, like low-speed vortexing and ethanol rinsing.