Mitf-D, a newly identified isoform, expressed in the retinal pigment epithelium and monocyte-lineage cells affected by Mitf mutations
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Published on: May 19, 2023
Kazuhisa Takeda1, Ken ichi Yasumoto, Naoko Kawaguchi
1Department of Molecular Biology and Applied Physiology, Tohoku University School of Medicine, Sendai, Miyagi, Japan.
Abstract:
Microphthalmia-associated transcription factor (Mitf) regulates the differentiation of melanocytes, optic cup-derived retinal pigment epithelium (RPE), and some types of bone marrow-derived cells. Mitf consists of at least five isoforms with different N-termini, each of which is encoded by a separate exon 1. Here we identified a novel isoform, termed mouse Mitf-D/human MITF-D, that is expressed in RPE, macrophages, and osteoclasts affected by the Mitf mutations, but not expressed in other Mitf target cells, including melanocyte-lineage cells and natural killer cells. The initiation Met of MITF-D is located in the downstream domain (B1b domain) that is shared by other MITF isoforms. The 5'-untranslated region of MITF-D mRNA is encoded by the newly identified first exon of the MITF gene, termed exon 1D, which is located 3 kb upstream of the exon encoding the B1b domain. Thus, the MITF gene generates multiple isoforms with different expression patterns by using the alternative promoters in a cell-dependent manner, thereby providing the molecular basis for the phenotypic variability seen in the MITF/Mitf mutants.
Insights
Researchers discovered a new Microphthalmia-associated transcription factor (Mitf) isoform, Mitf-D, in specific cells like RPE and macrophages. This finding explains the varied effects of Mitf mutations in different cell types.
Area of Science:
- Genetics
- Molecular Biology
- Developmental Biology
Background:
- Microphthalmia-associated transcription factor (Mitf) is crucial for cell differentiation.
- Mitf exists in multiple isoforms, each with distinct N-termini encoded by separate exon 1s.
Purpose of the Study:
- To identify and characterize novel Mitf isoforms.
- To elucidate the molecular basis for phenotypic variability in Mitf mutants.
Main Methods:
- Identification of a novel Mitf isoform (Mitf-D).
- Analysis of Mitf-D expression patterns in various cell types.
- Investigation of the genomic structure of the MITF gene, including alternative promoters and exon usage.
Main Results:
- A novel Mitf isoform, Mitf-D, was identified, specifically expressed in RPE, macrophages, and osteoclasts.
- Mitf-D utilizes a newly identified exon 1D, located upstream of the shared B1b domain.
- Expression of Mitf-D is restricted to specific cell types, unlike other Mitf isoforms.
Conclusions:
- The MITF gene employs alternative promoters for cell-dependent isoform generation.
- This isoform diversity provides a molecular explanation for the diverse phenotypes observed in Mitf/mitf mutants.
