- Cylindrical outer structure composed of a helical array of polymerized heterodimers of α- and β-tubulin.
- Each dimer has 2 GTP bound.
- Incorporated into flagella, cilia, mitotic spindles.
- Grows slowly, collapses quickly.
- Also involved in slow axoplasmic transport in neurons.
- Molecular motor proteins—transport cellular cargo toward opposite ends of microtubule tracks.
- Dynein—retrograde to microtubule (+ → −).
- Kinesin—anterograde to microtubule (− → +).
- Negative end Near Nucleus. Positive end Points to Periphery
- Drugs that act on microtubules (Microtubules Get Constructed Very Poorly):
- Mebendazole (antihelminthic)
- Griseofulvin (antifungal)
- Colchicine (antigout)
- Vincristine/Vinblastine (anticancer)
- Paclitaxel (anticancer)
- Cilia structure
- 9 doublet + 2 singlet arrangement of microtubules (A).
- Basal body (base of cilium below cell membrane) consists of 9 microtubule triplets B with no central microtubules.
- Axonemal dynein—ATPase that links peripheral 9 doublets and causes bending of cilium by differential sliding of doublets.
- Gap junctions enable coordinated ciliary movement.
- Kartagener syndrome (1° ciliary dyskinesia)
- immotile cilia due to a dynein arm defect.
- Autosomal recessive.
- Results in ↓ male and female fertility due to immotile sperm (compared to cystic fibrosis, which has an absent vas deferens) and dysfunctional fallopian tube cilia, respectively;
- ↑ risk of ectopic pregnancy.
- Can cause impaired mucociliary clearance, bronchiectasis, digital clubbing recurrent sinusitis, nasal polyps, chronic ear infections, conductive hearing loss, and situs inversus (eg, dextrocardia on CXR (C)).
- (Kartagener’s restaurant: take-out only, there’s no dynein “dine-in”).
- Diagnosis: Low nasal nitric oxide levels. Bronchoscopy and electron microscopic visualization of ciliary abnormalities. Genetic testing.