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Subfunctionalization of duplicate mitf genes associated with differential degeneration of alternative exons in fish
Joachim Altschmied1, Jacqueline Delfgaauw, Brigitta Wilde
1Department of Physiological Chemistry I, Biocenter (Theodor-Boveri Institute), University of Würzburg, D-97074 Würzburg, Germany.
Abstract:
The microphthalmia-associated transcription factor (MITF) exists in at least four isoforms. These are generated in higher vertebrates using alternative 5' exons and promoters from a single gene. Two separate genes (mitf-m and mitf-b), however, are present in different teleost fish species including the poeciliid Xiphophorus, the pufferfishes Fugu rubripes and Tetraodon nigroviridis, and the zebrafish Danio rerio. Fish proteins MITF-m and MITF-b correspond at both the structural and the expression levels to one particular bird/mammalian MITF isoform. In the teleost lineage subfunctionalization of mitf genes after duplication at least 100 million years ago is associated with the degeneration of alternative exons and, probably, regulatory elements and promoters. For example, a remnant of the first exon specific for MITF-m is detected within the pufferfish gene encoding MITF-b. Retracing the evolutionary history of mitf genes in vertebrates uncovered the differential recruitment of new introns specific for either the teleost or the bird/mammalian lineage.
Insights
The microphthalmia-associated transcription factor (MITF) gene evolved into two separate genes in fish, unlike in mammals where it has multiple isoforms from one gene. This gene duplication and subsequent subfunctionalization in teleosts occurred over 100 million years ago.
Area of Science:
- Evolutionary biology
- Molecular genetics
- Comparative genomics
Background:
- The microphthalmia-associated transcription factor (MITF) is crucial in vertebrates, typically existing as multiple isoforms derived from a single gene via alternative splicing in higher vertebrates.
- Teleost fish, however, possess two distinct MITF genes, mitf-m and mitf-b, suggesting a different evolutionary trajectory compared to mammals and birds.
Purpose of the Study:
- To investigate the evolutionary history and divergence of MITF genes in vertebrates, particularly focusing on teleost fish.
- To understand the mechanisms driving the evolution of MITF gene structure and regulation, including gene duplication and subfunctionalization.
Main Methods:
- Comparative genomic analysis of MITF genes across various vertebrate species, including teleost fish (Xiphophorus, Fugu rubripes, Tetraodon nigroviridis, Danio rerio) and higher vertebrates.
- Phylogenetic analysis to retrace the evolutionary history of MITF genes and identify patterns of intron recruitment.
- Examination of gene structure, including alternative exons, regulatory elements, and promoter regions.
Main Results:
- MITF proteins in teleost fish (MITF-m and MITF-b) structurally and expression-wise correspond to a single MITF isoform found in birds and mammals.
- Evidence suggests subfunctionalization of duplicated mitf genes in teleosts over 100 million years ago, accompanied by the degeneration of alternative exons and regulatory elements.
- A remnant of an MITF-m-specific exon is found within the MITF-b gene in pufferfish, indicating gene structure evolution.
- Differential recruitment of new introns occurred specifically in either the teleost or the bird/mammalian lineage during vertebrate evolution.
Conclusions:
- The evolution of MITF genes in teleosts involved gene duplication followed by subfunctionalization, leading to two distinct genes (mitf-m and mitf-b) with specialized roles.
- The observed degeneration of alternative exons and regulatory elements, along with differential intron gain, highlights the dynamic nature of gene evolution in vertebrates.
- Understanding MITF gene evolution provides insights into the diversification of transcription factor function across different vertebrate lineages.