Axoneme

Numerous eukaryotic cells carry whip-like appendages whose inner core consists of a cytoskeletal structure called the axoneme. The axoneme serves as the "skeleton" of these organelles, both giving support to the structure and, in some cases, causing it to bend. Though distinctions of function and/or length may be made between cilia and flagella, the internal structure of the axoneme is common to both.The building block of the axonmene is the microtubule; each axoneme is composed of several microtubules aligned in parallel. More specifically, the microtubules are arranged in a characteristic pattern known as the “9x2 + 2," as shown in the image at right. Nine sets of "doublet" microtubules form a ring around a "central pair" of single microtubules. Besides the microtubules, the axoneme contains many proteins and protein complexes necessary for its function. The dynein arms, for example, are motor complexes which produce the force needed for bending. Each dynein arm is anchored to a doublet microtubule; by "walking" along an adjacent microtubule, the dynein motors can cause the microtubules to slide against each other. When this is carried out in a synchronized fashion, with the mictrotubules on one side of the axonmene being pulled 'down' and those on the other side pulled 'up,' the axoneme as a whole can bend back and forth. This process is responsible for ciliary/flagellar beating, as in the well-known example of the human sperm.The radial spoke is another protein complex of the axoneme. Thought to be important in regulating the motion of the axoneme, this "T"-shaped complex projects from each set of outer doublets toward the central microtubules.The axoneme structure in non-motile primary cilium shows some variation from the canonical “9x2 + 2” anatomy. No dynein arms are found on the outer doublet microtubules, and there is no pair of central microtubule singlets. This organization of axoneme is referred as “9x2 + 0”. In addition, “9x2 + 1” axonemes, with only a single central microtubule, have been found to exist. (From the Wikpedia article Axoneme.)

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Recent Publications on Axoneme:
DNAJB13 is a Radial Spoke Protein of Mouse '9+2' Axoneme. Contents It has been shown that DNAJB13, a type II heat shock protein 40,...	19th November, 2009	Department of Cell and Molecular Biology, Karolinska Institutet,	Reprod Domest Anim. 2009 Nov 16. DOI Direct Link
Ratchetlike properties of in vitro microtubule translocation by a Chlamydomonas inner-arm dynein species c in the presence of flow. To investigate the force generation properties of Chlamydomonas axonemal...	18th November, 2009	Department of Biological Sciences, Graduate School of Science, University	Biophys J. 2009 Sep 16;97(6):1657-62. DOI Direct Link
Trafficking of membrane proteins to cone but not rod outer segments is dependent on heterotrimeric kinesin-II. Heterotrimeric kinesin-II is a molecular motor localized to the inner...	13th November, 2009	Department of Ophthalmology, University of Utah Health Science Center,	J Neurosci. 2009 Nov 11;29(45):14287-98. DOI Direct Link
Abnormal Spermatid Formation in the Presence of the Parasitic B(24) Chromosome in the Grasshopper Eyprepocnemis plorans. Morphology and size of spermatids were analysed in the grasshopper...	30th October, 2009	Departamento de Genetica, Universidad de Granada, Granada, Spain.	Sex Dev. 2009 Oct 28. DOI Direct Link
Distribution and structural diversity of cilia in tadpole larvae of the ascidian Ciona intestinalis. Accumulating evidence demonstrates that cilia play important roles in a...	20th October, 2009	Shimoda Marine Research Center, University of Tsukuba, Shimoda, Shizuoka	Dev Biol. 2009 Oct 14. DOI Direct Link
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Axoneme Patents:
US Patent No.	Title
7553674	Methods of identifying compounds useful for modulating intraflagellar transport
6660767	Coumarin compounds as microtubule stabilizing agents and therapeutic uses thereof
6642221	Vanadium compounds as anti-proliferative agents
6617156	Nucleic acid and amino acid sequences relating to Enterococcus faecalis for diagnostics and therapeutics
6610657	Alkyl peptide amides and applications
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