Undulipodia, flagella and cilia

Area of Science:

• Cell biology
• Microbiology
• Evolutionary biology

Background:

• The term 'flagella' is currently used ambiguously to describe distinct structures in prokaryotes and eukaryotes.
• Bacterial flagella are composed of flagellin protein, while eukaryotic flagella and cilia comprise microtubule proteins (tubulin) and ATPase (dynein).
• The structural and functional differences, particularly the near-identical nature of cilia and eukaryotic flagella versus their dissimilarity to prokaryotic flagella, are obscured by the current terminology.

Purpose of the Study:

• To propose the adoption of the term 'undulipodia' for eukaryotic cilia and flagella.
• To advocate for restricting the term 'flagella' exclusively to prokaryotic organelles.
• To establish clear, unambiguous terminology for microbial and cellular motility structures.

Main Methods:

• Review of existing scientific literature and terminology.
• Analysis of the structural and compositional differences between prokaryotic and eukaryotic flagella/cilia.
• Proposal for a revised nomenclature based on established scientific suggestions.

Main Results:

• Current terminology conflates distinct prokaryotic (bacterial flagella, spirochaete axial filaments) and eukaryotic (cilia, eukaryotic flagella) structures.
• Prokaryotic flagella are external, solid structures of flagellin lacking intrinsic motility.
• Eukaryotic undulipodia are internal, intrinsically motile structures with a 9-fold microtubule symmetry.

Conclusions:

• Adopting 'undulipodia' for eukaryotic cilia and flagella will resolve terminological ambiguity.
• Restricting 'flagella' to prokaryotic structures will improve clarity in scientific communication.
• This proposed nomenclature aligns with the distinct evolutionary origins and molecular compositions of these organelles.