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Joined 2026-09-21 Message
Incoming links: Motile cilium
Axoneme 2026-11-05
An axoneme is the organized microtubule-based core of a eukaryotic cilium or flagellum. It supplies a structural framework and, in motile forms, carries motor and linking components that turn relative microtubule sliding into movement. The axoneme is an internal assembly, not the entire membrane-covered projection.[ref]
Molecular Biology of the Cell, 4th edition by Bruce Alberts and others. Chapter 16, Cilia and Flagella: microtubule organization and sliding motors.
The familiar 9+2 arrangement contains nine outer doublets surrounding two central singlets. It describes spatial organization, not eleven identical independent tubules: each outer doublet has two associated tubules. Other axonemal arrangements occur, so the term does not require every cilium to have a central pair or to be motile.
An important mechanical test used isolated sea-urchin sperm axonemes. After brief treatment with trypsin, the preparations initially retained the characteristic organization, but addition of ATP caused active separation into individual tubules and groups. K. E. Summers and I. R. Gibbons interpreted these observations as evidence for sliding between the structural elements.[ref]
Adenosine triphosphate-induced sliding of tubules in trypsin-treated flagella of sea-urchin sperm by K. E. Summers and I. R. Gibbons. 1971 abstract: preserved starting architecture and ATP-induced active disintegration after digestion.
The experiment separates two roles that can otherwise be conflated. Motors such as dynein generate relative motion, while structural constraints normally keep sliding components in an organized assembly. Weakening the constraints reveals sliding as separation; preserving them permits bending. The disintegration experiment does not imply that a normally beating motile cilium repeatedly falls apart and rebuilds itself.