To identify the genes that determine differentiation phenotypes, we compared gene expression of pancreatic islet β- and α-cells, which are derived from the common precursor and secrete insulin and glucagon, respectively. The expression levels of homeotic genes including Hox genes known to determine region specificity in the antero-posterior (AP) body axis, tissue-specific homeobox genes, and other 8,734 genes were compared in a β- and α-cell line of MIN6 and αTC1.6. The expression of homeotic genes were surveyed with reverse transcription-polymerase chain reaction (RT-PCR) using degenerate primers corresponding to invariant amino acid sequences within the homeodomain and subsequently with specific primers. Expression of Hoxc6, Hoxc9, Hoxc10, Pdx1, Cdx2, Gbx2, Pax4, and Hlxb9 genes in MIN6 was higher than those in αTC1.6, while expression of Hoxa2, Hoxa3, Hoxa5, Hoxa6, Hoxa7, Hoxa9, Hoxa10, Hoxa13, Hoxb3, Hoxb5, Hoxb6, Hoxb13, Hoxb8, and Brain4 genes in αTC1.6 was higher than those in MIN6. Out of 8,734 mouse genes screened with high-density mouse cDNA microarrays for MIN6- and αTC1.6-derived cDNA, 58 and 25 genes were differentially over- and under-expressed in MIN6, respectively. GLUTag, which is derived from a large bowel tumor and expresses the proglucagon gene, showed a comparatively similar expression profile to that of αTC1.6 in both homeotic and other genes analyzed in cDNA microarray.
Our results are consistent with the interpretation that not only the tissue-specific homeotic genes, but also Hox genes are related to differentiation phenotypes of pancreatic β- and α-cells rather than their regional specification of the body in vertebrates
