Heterogeneity in codon usage in the flatworm Schistosoma mansoni

Area of Science:

• Genomics and Molecular Biology
• Parasitology
• Bioinformatics

Background:

• Synonymous codon usage varies significantly across genes in the parasitic flatworm Schistosoma mansoni.
• Understanding codon usage patterns is crucial for deciphering gene expression regulation and evolutionary pressures in parasites.

Purpose of the Study:

• To investigate the factors shaping synonymous codon usage variation among Schistosoma mansoni genes.
• To determine the relative contributions of mutational biases versus selection to codon usage patterns.

Main Methods:

• Principal components analysis (PCA) was employed to identify major trends in codon usage.
• Analysis of the effective number of codons (ENC) and its relationship with GC content at the third codon position (GC3).
• Correlation analysis of GC content across different genomic regions (exons, 5', 3', introns).

Main Results:

• A single major trend in codon usage was identified, strongly correlating with GC content in exons and third codon positions.
• Codon usage patterns did not distinguish between putatively highly and lowly expressed genes.
• The distribution of ENC against GC3 suggests that mutational biases are the primary drivers of codon usage.
• Significant correlations were observed between GC content in various genomic regions, indicating potential genome-wide GC content variations.

Conclusions:

• Mutational biases, rather than selection related to expression levels, appear to be the main force shaping codon usage in Schistosoma mansoni.
• Genomic structure and regional GC content variations are likely significant factors influencing codon usage.
• While selection cannot be entirely excluded, its role appears secondary to mutational influences in this species.