Alpha-fetoprotein is dynamically expressed in rat pancreas during development

To identify proteins involved in pancreatic development, we used a differential proteomics approach by comparing pancreatic extracts from four biologically significant stages of development: embryonic day (E) 15.5, E18.5, postnatal (P) days 0 and adult. By two-dimensional gel electrophoresis (2D-E) and MALDI-TOF MS (Matrix Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectrometry) following database searching and protein annotation, 15 proteins were identified as being differently expressed in the pancreas between the four phases. The expression pattern and the localization of alpha-fetoprotein (AFP), one of significant changed proteins observed, were further determined. Four isoforms of AFP (72 kDa, 60 kDa, 48 kDa and 37 kDa) were found by Western blotting in the pancreas tested, most of them showed a stronger signal in E18.5 followed by a steady decrease and only a 60-kDa isoform was detected in the adult pancreas. Immunolocalization for AFP revealed that a positive reactivity was detectable at E15.5 pancreas, became stronger in the cytoplasm of mesenchyme cells at E18.5, and declined after birth to a nearly undetectable level in adults. The dynamic expression of AFP in rat pancreas from different stages indicates that AFP might be involved in some aspects of pancreatic development.