Runaway GC Evolution in Gerbil Genomes

Area of Science:

• Genomics and Evolutionary Biology
• Molecular Evolution
• Mammalian Genetics

Background:

• Recombination influences local GC-content through GC-biased gene conversion (gBGC).
• The fat sand rat (Psammomys obesus) exhibits a large genomic region with extreme GC-content, serving as a model for gBGC studies.
• Understanding gBGC's role in chromosome evolution requires comparative genomic analysis.

Purpose of the Study:

• To compare GC-content and GC-to-AT substitution patterns in gerbils and murine rodents.
• To investigate the evolutionary mechanisms driving high GC-content in specific genomic regions.
• To assess the potential for rapid GC-content evolution in mammalian genomes.

Main Methods:

• Comparative analysis of GC-content and substitution patterns across protein-coding genes in four gerbil species and two murine rodents.
• Examination of synonymous and nonsynonymous substitution rates for various mutational categories (AT-to-GC, GC-to-AT, GC-conservative).
• Identification and clustering analysis of genes exhibiting outlying AT-to-GC substitution rates.

Main Results:

• A high-GC region, previously identified in Psammomys obesus, is conserved across gerbil species.
• This region shows elevated substitution rates across all mutation types, with a higher AT-to-GC than GC-to-AT rate, consistent with increasing GC-content.
• Over 300 genes outside the known region display high AT-to-GC rates in gerbils, with many forming large, megabase-scale clusters, suggesting widespread high recombination.

Conclusions:

• Gerbil species exhibit unusual GC-skewed substitution patterns, indicative of genomic regions with exceptionally high recombination rates.
• These findings suggest that rapid GC-content evolution, driven by gBGC, is possible in mammals.
• Gerbils provide a valuable model system for studying the mechanisms and consequences of GC-biased gene conversion.