Non-isotopic detection of in situ nucleic acid in cervix: an updated protocol.

Recently, sensitive non-isotopic in situ hybridisation (NISH) methodology for the detection of human DNA and human papilloma virus (HPV) DNA in archival paraffin blocks of cervix was described. An amended protocol, now used in this laboratory for detection of these genes by NISH is presented. The amendments include the following: protease digestion at 37 degrees C; tissue dehydration in air rather than ethanol; stringency washing in formamide solution; blocking non-specific binding of avidin alkaline phosphatase with a modified buffer; and increasing the concentration of avidin alkaline phosphatase for detecting low abundance DNA. These changes simplify and increase the sensitivity of the protocol such that "Y" chromosome repeats are visualised in almost all female cells.