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.
Watada
H
H
Hormone Research Institute, University of California, San Francisco, California 94143-0534, USA.
Mirmira
R G
RG
Leung
J
J
German
M S
MS
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