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Molecular cloning of cDNA encoding a novel microphthalmia-associated transcription factor isoform with a distinct
N Fuse1, K i Yasumoto, K Takeda
1Department of Molecular Biology and Applied Physiology Saitama Cancer Center, Saitama 362-080, Japan.
Abstract:
Microphthalmia-associated transcription factor (MITF) is a basic helix-loop-helix-leucine zipper protein, and plays an important role in the development of various cell types, such as neural-crest-derived melanocytes and optic-cup-derived retinal pigment epithelium. Three isoforms of MITF with distinct amino-termini have been described. These include melanocyte lineage-specific MITF-M, heart-type MITF-H, and the recently identified MITF-A. Here we identify a fourth isoform, MITF-C, with a unique amino-terminus of 34 amino acid residues, which shares about 43% sequence identity with putative transactivation segments of two previously identified leukemogenic factors, ENL and AF-9. Reverse transcription-polymerase chain reaction analysis revealed that MITF-C mRNA is expressed in many cell types, including retinal pigment epithelium, but is undetectable in melanocyte-lineage cells. In contrast, MITF-A and MITF-H mRNAs are coexpressed in all cell types examined. Transient cotransfection assays suggested that MITF-C, like other MITF isoforms, functions as a transcriptional activator of certain target genes, but its transactivation specificity for the target promoters is different from those of other MITF isoforms. Therefore, isoform multiplicity provides MITF with differential expression patterns as well as functional diversity.
Insights
Researchers discovered a new MITF-C isoform, a transcription factor crucial for cell development. This new isoform exhibits unique expression patterns and functional diversity compared to other MITF forms.
Area of Science:
- Molecular Biology
- Developmental Biology
- Genetics
Background:
- The Microphthalmia-associated transcription factor (MITF) is vital for neural-crest-derived melanocytes and optic-cup-derived retinal pigment epithelium development.
- Three MITF isoforms (MITF-M, MITF-H, MITF-A) with distinct amino-termini have been previously identified.
Purpose of the Study:
- To identify and characterize novel isoforms of the Microphthalmia-associated transcription factor (MITF).
- To investigate the expression patterns and functional diversity of MITF isoforms.
Main Methods:
- Reverse transcription-polymerase chain reaction (RT-PCR) was used to analyze MITF mRNA expression.
- Transient cotransfection assays were employed to assess the transcriptional activity of MITF isoforms.
Main Results:
- A fourth MITF isoform, MITF-C, was identified with a unique 34-amino acid amino-terminus.
- MITF-C mRNA is expressed in retinal pigment epithelium but not in melanocyte-lineage cells.
- MITF-C functions as a transcriptional activator with distinct promoter specificity compared to other MITF isoforms.
Conclusions:
- The discovery of MITF-C expands the known repertoire of MITF isoforms.
- MITF isoform multiplicity contributes to differential gene expression and functional diversity in cellular development.