WHICH EVOLUTIONARY FORCES DICTATE CODON USAGE IN HUMAN TESTIS SPECIFIC GENES?
Objective: Unequal usage of synonymous codons encoding an amino acid is termed as codon usage bias. Synonymous codon usage bias is an inevitable phenomenon in organismic taxa across the three domains of life, i.e. plants, animals and microbes. Here we report the codon usage pattern in human testis-specific genes found in Y chromosome. Testis-specific genes are associated with several dysfunctions, such as gonadal sex reversion, infertility, gonadoblastoma and non-syndromic hearing impairment.
Methods: We used bioinformatics approaches to analyze codon usage bias in human testis-specific genes
Results: Highly significant negative correlation was found between ICDI and tAI (r=-0.939**, p<0.01). Moreover, highly significant positive correlation between A% and A3% (r =0.774*, p<0.05), T and T3% (r=0.894**, p<0.01), GC% and GC3% (r = 0.897**, p<0.01) suggest that mutation pressure played an important role in codon usage pattern of these genes. However, significant positive correlation between G and G3 % (r =0.936**, p<0.01), G and C3 (r=0.557, p>0.05) but negative correlation between GC and T3 % (r=-0.960**, p<0.01) indicate the role of natural selection on codon bias. Variation of codon usage pattern was also evident in different genes from principal component analysis (PCA).
Conclusion: Codon usage bias in human testis-specific genes is low. These genes are rich in GC content. Both natural selection and mutation pressure affect the codon usage bias in these genes.
Keywords: Codon usage bias, Mutation pressure, Natural selection
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