REG gene expression in inflamed and healthy colon mucosa explored by in situ hybridisation

The regenerating islet-derived (REG) gene family encodes a group of proteins highly expressed in several human pathologies, many of which are associated with epithelial inflammation. All human family members, namely REG1A, REG1B, REG3A and REG4, are closely related in genomic sequence and all are part of the c-type lectin superfamily. REGs are highly expressed during inflammatory bowel disease (IBD)-related colonic inflammation and the in vivo expression pattern of REG1A and REG4 has been localised by using immunohistochemistry. However, the function of the encoded proteins is largely unknown and the cellular localisation of REG expression during colonic inflammation has not been described. Therefore, we have used in situ hybridisation to demonstrate the cellular localisation of REG expression in healthy and diseased colonic mucosa. Samples drawn from an IBD cohort including both inflamed and un-inflamed colonic mucosa are described, as are samples from non-IBD inflammation and healthy controls. Immunohistochemistry against known cell-type markers on serial sections has localised the expression of REGs to metaplastic Paneth cells (REG1A, REG1B and REG3A) and enteroendocrine cells (REG4), with a marked expansion of expression during inflammation. The group of REGs can, based on gene expression patterns, be divided into at least two groups; REG1A, REG1B and REG3A with their expression focused in the crypt base spreading from Paneth cells and REG4 being more highly expressed towards the luminal face. This exploration of expression pattern forms provides the background for further exploration of REG function in the intestine.