Turtle isochore structure is intermediate between amphibians and other amniotes

Area of Science:

• Comparative genomics
• Molecular evolution
• Bioinformatics

Background:

• Vertebrate genomes contain isochores, long DNA regions with distinct base compositions (GC-rich or AT-rich).
• Mammalian and archosaur genomes are GC-rich, while amphibian and fish genomes are more homogeneous and AT-rich.
• Higher GC content correlates with DNA thermostability, leading to hypotheses that GC-richness is an adaptation to higher body temperatures.

Purpose of the Study:

• To investigate the GC content and isochore structure of the turtle genome.
• To test the hypothesis that elevated GC content in vertebrate genomes is an adaptation to thermoregulation.
• To provide genomic data for reptiles to facilitate future reptilian genomics studies.

Main Methods:

• Comparative analysis of expressed genes from the red-eared slider turtle.
• Analysis of orthologous genes in mammalian, archosaurian, and amphibian genomes.
• Examination of GC content at the third-codon-position of expressed sequence tags (ESTs).

Main Results:

• The turtle genome exhibits an intermediate GC content, falling between GC-poor amphibians and GC-rich mammals and archosaurs.
• A strong correlation was observed between the GC content of turtle genes and other vertebrate genes.
• The isochore structure of turtles appears intermediate between amphibians and other amniotes.

Conclusions:

• The findings are consistent with thermal hypotheses regarding isochore evolution.
• The study expands the genomic data available for reptiles, supporting further research.
• While supporting thermal hypotheses, multiple models for isochore evolution remain plausible.