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Minisatellite instability at the Adh locus reveals somatic polymorphism in amphioxus
Cristian Cañestro1, Roser Gonzàlez-Duarte, Ricard Albalat
1Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal, 645, E-08028 Barcelona, Spain.
Nucleic Acids Research
|June 28, 2002
Summary
Genetic variation in amphioxus genes, like alcohol dehydrogenase (Adh3), originates from unstable minisatellites, not just germline changes. These repetitive DNA sequences, called mirages, create mosaic animals through somatic events.
Area of Science:
- Evolutionary biology
- Genetics
- Molecular biology
Background:
- Amphioxus (Cephalochordata) is crucial for understanding vertebrate evolution due to its close relationship to vertebrates.
- Amphioxus genes exhibit high polymorphism, but the sources of this genetic variability remain unclear.
- Repetitive DNA sequences are known contributors to genetic diversity in various organisms.
Purpose of the Study:
- To investigate the origin and nature of genetic variability in amphioxus genes.
- To analyze the alcohol dehydrogenase 3 (Adh3) locus in two amphioxus species.
- To determine the role of repetitive DNA sequences in generating genetic diversity.
Main Methods:
- Analysis of the alcohol dehydrogenase locus (Adh3) in Branchiostoma lanceolatum and Branchiostoma floridae.
- Small pool-PCR assays to assess allelic variants and minisatellite instability.
- Identification and characterization of repetitive DNA sequences, including novel minisatellite classes.
Main Results:
- Genetic variation at the Adh3 locus is strongly associated with repetitive DNA sequences, primarily minisatellites.
- Minisatellite instability, detected via small pool-PCR, is the mechanism generating allelic variants.
- A novel class of minisatellites, termed 'mirages,' was identified, characterized by repeat subunits spanning exon-intron boundaries.
- Somatic events, rather than germline processes, appear to be the main drivers of new variant generation, leading to mosaic adult amphioxus.
- Despite spanning splice sites, these mirage minisatellites did not result in detectable aberrant mRNA variants.
Conclusions:
- Genetic variability in amphioxus is significantly influenced by minisatellite instability, particularly through somatic processes.
- The discovery of 'mirage' minisatellites provides new insights into the evolution of repetitive DNA and gene regulation.
- Amphioxus exhibits mosaicism at the molecular level due to somatic variation, impacting our understanding of its genome evolution.