Author reply to: RUNX3 is expressed in the epithelium of the gastrointestinal tract

The article by Levanon et al (2011) reports that expression of the transcription factor Runx3 is undetectable in gastrointestinal (GIT) epithelium. These results contradict our results, particularly those in Li et al (2002), which indicate that Runx3 is strongly expressed and functions as tumour suppressor in GIT. Here, I aim to clarify the issues by summarizing the findings associated with this controversy. Li et al (2002) (Fig 1I) indicated that mouse Runx3 RNA is expressed primarily in the lower part of the gastric gland where pepsinogen-producing chief cells reside (reproduced here in Fig 1A). Subsequently, we demonstrated the presence of RUNX3 protein in chief cells of human gastric epithelium by immunohistochemistry (IHC; Fig 1B), which was further validated by in situ hybridization (Ito et al, 2005; Fig 1C). Overall, remarkably similar RUNX3 RNA and protein expression patterns in human and mouse gastric epithelium were obtained by three different individuals, 3 years apart. In contrast to these observations, Levanon et al (2011) claim that RUNX3 is absent from mouse GIT