title: Immunohistochemical assessment of Pax8 expression during pancreatic islet development and in human neuroendocrine tumors.
abstract: The paired box transcription factor Pax8 is critical for development of the eye, thyroid gland as well as the urinary and reproductive organs. In adult, Pax8 overexpression is associated with kidney, ovarian and thyroid tumors and has emerged as a specific marker for these cancers. Recently, Pax8 expression was also reported in human pancreatic islets and in neuroendocrine tumors, identifying Pax8 as a novel member of the Pax family expressed in the pancreas. Herein, we sought to provide a comprehensive analysis of Pax8 expression during pancreogenesis and in adult islets. Immunohistochemical analysis using the most employed Pax8 polyclonal antibody revealed strong nuclear staining in the developing mouse pancreas and in mature human and mouse islets. Astonishingly, Pax8 mRNA in mouse islets was undetectable while human islets exhibited low levels. These discrepancies raised the possibility of antibody cross-reactivity. This premise was confirmed by demonstrating that the polyclonal Pax8 antibody also recognized the islet-enriched Pax6 protein both by Western blotting and immunohistochemistry. Thus, in islets polyclonal Pax8 staining corresponds mainly to Pax6. In order to circumvent this caveat, a novel Pax8 monoclonal antibody was used to re-evaluate whether Pax8 was indeed expressed in islets. Surprisingly, Pax8 was not detected in neither the developing pancreas or in mature islets. Reappraisal of pancreatic neuroendocrine tumors using this Pax8 monoclonal antibody exhibited no immunostaining as compared to the Pax8 polyclonal antibody. In conclusion, Pax8 is not expressed in the pancreas and cast doubts on the value of Pax8 as a pancreatic neuroendocrine tumor marker.
authors.affiliation: Pancreatic Islet Development and Regeneration Unit, Department of Stem Cells, Andalusian Center for Molecular Biology and Regenerative Medicine, Seville, Spain.
authors.forename: Petra I
authors.initials: PI
authors.lastname: Lorenzo
authors.forename: Carmen M
authors.initials: CM
authors.lastname: Jimenez Moreno
authors.forename: Irene
authors.initials: I
authors.lastname: Delgado
authors.forename: Nadia
authors.initials: N
authors.lastname: Cobo-Vuilleumier
authors.forename: Raphael
authors.initials: R
authors.lastname: Meier
authors.forename: Lourdes
authors.initials: L
authors.lastname: Gomez-Izquierdo
authors.forename: Thierry
authors.initials: T
authors.lastname: Berney
authors.forename: Rocio
authors.initials: R
authors.lastname: Garcia-Carbonero
authors.forename: Anabel
authors.initials: A
authors.lastname: Rojas
authors.forename: Benoit R
authors.initials: BR
authors.lastname: Gauthier
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D014408:Biomarkers, Tumor / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D003429:Cross Reactions; D004622:Embryo, Mammalian / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D007515:Islets of Langerhans / Q000196:embryology* / Q000378:metabolism; D007668:Kidney / Q000196:embryology / Q000378:metabolism; D008099:Liver / Q000196:embryology / Q000378:metabolism; D051379:Mice; D018358:Neuroendocrine Tumors / Q000378:metabolism* / Q000473:pathology; D000072636:PAX8 Transcription Factor; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism*; D010179:Pancreas / Q000196:embryology / Q000378:metabolism; D010190:Pancreatic Neoplasms / Q000378:metabolism* / Q000473:pathology; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D014408:Biomarkers, Tumor; D000072636:PAX8 Transcription Factor; C083325:PAX8 protein, human; D051761:Paired Box Transcription Factors; C499496:Pax8 protein, mouse; D012333:RNA, Messenger