High quality genomic DNA extraction from large milk samples

摘要

Recently, techniques have been reported which describe the isolation of genomic DNA from somatic cells of bovine milk (Lipkin et al. 1993, 1998), epithelial cells of human milk (Lindquist et al. 1994) and bovine and caprine milk (Amills et al. 1997). In each of these reports, somatic cell DNA was successfully amplified by polymerase chain reaction (PCR). However, none of these methods are suitable for large-scale genotyping projects, because consistent quantifiable amounts of good quality genomic DNA were not obtained from milk somatic cells, or because good quality PCR product could not consistently be amplified from genomic DNA. The somatic cell count (SCC) in bovine milk increases in response to infection from a low range between 2 x 10~4 and 2 x 10~5 cells/ml from a healthy quarter, to a high range from 3 x 10~5 to 1 x 10~7 cells/ml from an infected quarter (Holmes & Wilson, 1984; Kehrli & Shuster, 1994). In whole blood, the numbers of white blood cells (nucleated cells which can yield genomic DNA) also vary in response to infection, ranging between 7 x 10~6 and 1 x 10~7 cells/ml (Swenson, 1993). Whole blood can contain up to 350 times more nucleated cells than milk, when comparing lower cell counts for the same volumes of whole blood and milk.