MESSENGER-RNA PROFILING OF RAT ISLET TUMORS REVEALS NKX-6.1 AS A BETA-CELL-SPECIFIC HOMEODOMAIN TRANSCRIPTION FACTOR

Development of a high capacity multiplex reverse transcriptase-polymer ase chain reaction protocol has allowed us to screen lineage related r at islet tumors classified as alpha-, beta-, and delta-like as judged by their hormone profile for differential expression of more than 50 s elected genes, We find that in addition to insulin the insulinoma expr ess the normal beta-cell markers Pdx-1, IAPP, and Glut-2, and that the se markers are absent from the glucagonoma: a reflection of the normal alpha-cell, Furthermore, this study suggests that the GLP-1, glucagon , GIP, IGF-1, and insulin receptors as well as E-cadherin, R-cadherin, Id-1, and Id-2 are differentially expressed within the islet of Lange rhans, Importantly, insulinoma-specific expression of the recently clo ned homeodomain protein Nkx 6.1 predicted beta-cell-specific expressio n in the normal islet, Immunohistochemistry using antibodies raised ag ainst recombinant Nkx 6.1 did indeed localize Nkx 6.1 expression exclu sively to the nuclei of normal islet beta-cells, Apart from pancreatic islets only the antral part of the stomach contained Nkx 6.1 mRNA, We conclude that multiplex reverse transcriptase-polymerase chain reacti on-based mRNA profiling is a powerful tool to identify differentially expressed genes within phenotypically related cells and propose that N kx 6.1 is involved in specifying the unique characteristics of the bet a-cell.