Southwestern histochemistry as a molecular histochemical tool for analysis of expression of transcription factors: application to paraffin-embedded tissue sections.

Southwestern histochemistry is used to localize transcription regulatory factors that bind to specific sequences of DNA and regulate the transcriptional activity of the genes, using a haptenized double-stranded DNA. This method has been developed in fresh frozen sections, but it was difficult to detect a specific signal in paraffin sections. In this review, we focus on the use of Southwestern histochemistry in paraffin sections. To detect a reliable signal in paraffin sections, we autoclaved or microwaved the sample before incubation with probe DNA. As a model system, we assessed estrogen receptor (ER) in paraffin sections of mouse ovary. ER was detected by Southwestern histochemistry in autoclaved or microwaved paraffin sections, and no signal was detected without such pretreatment. The ER staining pattern detected by Southwestern histochemistry was well consistent with that of ER alpha and ER beta detected by immunohistochemistry. Next, we analyzed the expression of cyclic adenosine monophosphate (cAMP)-responsive element binding protein (CREB) in regenerating livers of rats and mice. CREB was detected in hepatocyte nuclei in autoclaved paraffin sections by Southwestern histochemistry. Immunohistochemistry of CREB displayed homogeneous staining in hepatocyte nuclei, while the signal detected by Southwestern histochemistry showed a heterogeneous speckled pattern in the nuclei. CREB expression increased prior to the induction of proliferating cell nuclear antigen (PCNA). Because the PCNA gene has a cAMP-responsive element in its promoter, it can be suggested that CREB may activate the PCNA gene and lead to the induction of hepatocyte DNA synthesis. Our results indicate that autoclave or microwave treatment is very useful for Southwestern histochemistry in paraffin-embedded sections.