Classification and characterization of human endogenous retroviruses; mosaic forms are common

Area of Science:

• Genomics
• Virology
• Bioinformatics

Background:

• Human endogenous retroviruses (HERVs) are remnants of ancient retroviral infections integrated into the human genome.
• Existing HERV classifications are complex and lack a unifying structure.
• A systematic and simple classification is needed to understand HERV variation.

Purpose of the Study:

• To develop a systematic and unifying classification for human endogenous retroviruses (HERVs).
• To characterize HERV sequences and their relationships within the human genome.
• To provide a framework for understanding HERV diversity and evolution.

Main Methods:

• Analysis of the human genome assembly (GRCh 37/hg19) using RetroTector.
• Application of a novel similarity image analysis (Simage) for discriminating canonical and noncanonical HERVs.
• Multi-step classification procedure based on sequence similarity, existing clades, and taxonomic markers.

Main Results:

• Identified 3173 HERV sequences, classifying 1214 as canonical into 39 clades across three classes.
• Discovered 1959 noncanonical HERVs with 31 additional groups, revealing mosaicism through recombination and secondary integration.
• Envelope subgroups were defined, and "env snatching" (recombination involving envelope genes) was identified as common.

Conclusions:

• A comprehensive classification and characterization approach for all endogenous retroviruses (ERVs) was established.
• Recombination, particularly involving envelope genes, is a frequent occurrence among HERV ancestors.
• The new classification provides a clearer framework for studying HERV diversity and evolutionary history.