[Show abstract][Hide abstract] ABSTRACT: To define a genetic network that regulates development of the pancreas, we used high-density microarray (Affymetrix) to generate transcriptional profiles of rat pancreas from five biologically significant stages of development: embryonic day 12.5 (E12.5), E15.5, E18.5, postnatal day 0 (P0) and adult. Many genes were notably highly expressed in the later gestation when islet architecture and function are gradually forming. The expression and localization of mesothelin, one of these genes, was further examined. Reverse transcription-polymerase chain reaction and Western blot analysis revealed that mRNA and protein levels of mesothelin were high from later gestation to 2-3 weeks after birth, and with relatively low but detectable expression levels in adult rat pancreas. Immunolocalization indicated that mesothelin localized not only in islet beta-cells but also in the mesenchyme of developing rat pancreas. Transient mesothelin expression was concomitant with the development of islets architecture formation, remodeling and maturation. These findings indicate that mesothelin is dynamically expressed in the developing rat pancreas and that mesothelin might be involved in some developmental events during development of rat pancreas.