Expansion
Microfilaments, intermediate filaments and microtubules, in increasing size
Expansion
| Filament | Diameter | Protein | Role |
|---|---|---|---|
| Microfilaments | 7 nm | Actin | Contraction, cell shape, microvilli, cytokinesis |
| Intermediate filaments | 10 nm | Tissue specific | Structural strength |
| Microtubules | 25 nm | Tubulin | Transport, mitotic spindle, cilia, flagella |
Intermediate filament types are diagnostically vital:
- Cytokeratin: epithelial, so carcinoma
- Vimentin: mesenchymal, so sarcoma
- Desmin: muscle
- Glial fibrillary acidic protein: glial cells, so glioma
- Neurofilament: neurones
A tumour of unknown origin is stained for these markers, and the pattern identifies the lineage, which determines treatment.
Microtubules are the target of important drugs: vinca alkaloids prevent assembly and taxanes prevent disassembly, both arresting mitosis; colchicine inhibits neutrophil migration in gout; and griseofulvin acts similarly in fungi.
Cilia have a 9 plus 2 microtubule arrangement with dynein arms; defective dynein causes primary ciliary dyskinesia, with bronchiectasis, sinusitis, situs inversus and infertility.