Characterization of the human gene encoding cytokeratin 17 and its expression pattern

Area of Science:

• Molecular Biology
• Cell Biology
• Genetics

Background:

• Cytokeratin 17 (CK 17) exhibits an unusual expression pattern, primarily in basal cells of complex epithelia, distinguishing it from other cytokeratins.
• Its unique expression and potential role in tumor diagnosis necessitate a thorough characterization of the CK 17 gene and its product.

Purpose of the Study:

• To characterize the gene(s) encoding CK 17 and its cDNA-derived amino acid sequence.
• To investigate the genomic organization and evolutionary origins of CK 17 and its pseudogenes.
• To elucidate the transcriptional regulation and expression patterns of the CK 17 gene.

Main Methods:

• Isolation of a CK 17 cDNA clone from a HeLa cell library.
• Screening of human genomic libraries to identify CK 17 gene loci and pseudogenes.
• DNA methylation analysis, S1-nuclease protection assays, and Northern blot hybridization to study gene expression and regulation.

Main Results:

• Identified a functional CK 17 gene approximately 5 kbp upstream of the CK 16 gene, along with two unprocessed CK 17 pseudogenes.
• The CK 17 gene locus appears to have evolved through duplication events of larger gene clusters.
• Functional and pseudogene loci differ in DNA methylation patterns; CK 17 expression is primarily regulated at the transcriptional level, with a single transcriptional start site identified.

Conclusions:

• CK 17 gene expression is restricted, supporting its role as a marker for basal cell differentiation in complex epithelia.
• CK 17 may serve as an indicator for a specific type of epithelial stem cell.
• The findings provide insights into the evolution and regulation of cytokeratin genes.