Molecular evolution of human T-cell leukemia virus

Area of Science:

• Virology
• Molecular Evolution
• Phylogenetics

Background:

• Human T-cell leukemia virus type I (HTLV-I) is a significant human pathogen.
• Understanding the evolutionary history and genetic diversity of HTLV-I is crucial for public health.

Purpose of the Study:

• To construct phylogenetic trees for HTLV-I and related viruses using LTR and tax gene sequences.
• To investigate the evolutionary relationship between these viruses and their hosts.
• To assess the genetic variability and functional constraints of HTLV-I genes.

Main Methods:

• Phylogenetic analysis using nucleotide sequences of the long terminal repeat (LTR) and tax gene.
• Estimation of nucleotide diversity for HTLV-I tax genes.
• Examination of functional constraints on the overlapping rex and tax genes.

Main Results:

• Phylogenetic trees revealed two distinct viral groups (primate and bovine hosts) diverging from a common ancestor.
• Viral phylogeny differed from host phylogeny, indicating independent evolution and past interspecies transmission.
• HTLV-I tax gene nucleotide diversity (0.025) is higher than human globin genes but lower than influenza A hemagglutinin genes.
• The tax gene shows stronger constraints against amino acid changes than the rex gene in their overlapping region.

Conclusions:

• HTLV-I and related viruses evolved independently of host-species divergence, with evidence of interspecies transmission.
• HTLV-I possesses intermediate genetic variability compared to nuclear and typical RNA viruses.
• Functional constraints differ between the rex and tax genes, with tax being more conserved.