Evidence supporting a viral origin of the eukaryotic nucleus

Area of Science:

• Cell Biology
• Virology
• Evolutionary Biology

Background:

• The eukaryotic nucleus, a hallmark of eukaryotic cells, separates transcription from translation.
• The origin of the nucleus is a fundamental question in evolutionary biology.

Purpose of the Study:

• To present an updated Viral Eukaryogenesis (VE) hypothesis for the origin of the eukaryotic nucleus.
• To investigate the viral origins of nuclear functions, specifically transcription-translation uncoupling.

Main Methods:

• Phylogenetic analysis of the 7-methylguanylate (m7G) capping apparatus.
• Comparison of m7G capping machinery in eukaryotes, Mimiviridae, and archaea (including Lokiarchaeota).

Main Results:

• Homologues of the eukaryotic m7G capping apparatus are found in Mimiviridae viruses but not generally in archaea.
• Phylogenetic analysis indicates a common ancestral source for the m7G capping pathway in eukaryotes and Mimiviridae, predating the Last Eukaryotic Common Ancestor (LECA).

Conclusions:

• The eukaryotic nucleus and Mimiviridae likely acquired the m7G capping pathway from a common viral ancestor, the 'First Eukaryotic Nuclear Ancestor' (FENA).
• This supports the VE hypothesis, suggesting viral origins for key nuclear features and the uncoupling of transcription from translation.