Transcriptional and translational regulation of beta-cell differentiation factor Nkx6.1.
In the mature pancreas, the homeodomain transcription factor Nkx6.1 is uniquely restricted to beta-cells. Nkx6.1 also is expressed in developing beta-cells and plays an essential role in their differentiation. Among cell lines, both beta- and alpha-cell lines express nkx6.1 mRNA; but no protein can be detected in the alpha-cell lines, suggesting that post-transcriptional regulation contributes to the restriction of Nkx6.1 to beta-cells. To investigate the regulator of Nkx6.1 expression, we outlined the structure of the mouse nkx6.1 gene, and we identified regions that direct cell type-specific expression. The nkx6.1 gene has a long 5'-untranslated region (5'-UTR) downstream of a cluster of transcription start sites. nkx6.1 gene sequences from -5.6 to +1.0 kilobase pairs have specific promoter activity in beta-cell lines but not in NIH3T3 cells. This activity is dependent on sequences located at about -800 base pairs and on the 5'-UTR. Electrophoretic mobility shift assays demonstrate that homeodomain transcription factors PDX1 and Nkx2.2 can bind to the sequence element located at -800 base pairs. In addition, dicistronic assays establish that the 5'-UTR region functions as a potent internal ribosomal entry site, providing cell type-specific regulation of translation. These data demonstrate that complex regulation of both Nkx6.1 transcription and translation provides the specificity of expression required during pancreas development.
Hormone Research Institute, University of California, San Francisco, California 94143-0534, USA.
H
H
Watada
R G
RG
Mirmira
J
J
Leung
M S
MS
German
D020121:5' Untranslated Regions; D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D004247:DNA; D005786:Gene Expression Regulation; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D007515:Islets of Langerhans / Q000166:cytology*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D014176:Protein Biosynthesis; D017384:Sequence Deletion; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D029961:Zebrafish Proteins
D020121:5' Untranslated Regions; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins; C000715627:Nkx2-2 protein, mouse; C491328:Nkx6-1 protein, mouse; D014157:Transcription Factors; D029961:Zebrafish Proteins; C000715630:nkx2.2b protein, zebrafish; D004247:DNA