Cilia, centrioles andciliogenesis

MG 5607Shubhra Majumder

What are cilia or flagella?

Cilia are ‘hair-like’ projections fromcell surface

Primary cilia Centrosomes DNA

A. Why cilia are important?

B. How are they formed?B. How are they formed?

Bacterial flagella are not structurallysimilar to eukaryotic flagella

Figure 15-71a: MolecularBiology of the Cell

• Bacterial flagella help in motility and rotation

• A flagellum is made of Basal body, Hook andFilament

• Bacterial flagella are not microtubule-based

• The major component is Flagellin

Subtypes of cilia

Flagella inunicellulareukaryotes

Cilia

Non-motile ciliaMotile cilia

Motile cilia inmulticiliated cells

Sperm flagellum

Flagella provide motility

High speed video microscopy of a Chlamydomonas reinhardtiicell movement using newly developed “Cell LOcating withNanoscale Accuracy (CLONA)” video analysis method

(Fujita et al., Biophys J, 2014)

Ciliary beating regulates fluid flow

Video microscopy of mouse tracheal epithelial cells(Lechtreck K-F. et al., J Cell Biol. 2008)

Multiciliated cells are found in epithelia of respiratory tract,ependyma of brain ventricles etc.

Primary cilium as sensory organMost vertebrate cells contain primary cilia at some point, usually whenthey are differentiated (non-proliferating)

Primary cilia transduce chemical, mechanical or developmental signal

Extra-cellular sensory signaling: Primary cilia in Olfactory sensoryneurons, photoreceptor cells of retina

Mechanical sensor: Cilia in the epithelial cells of renal tubes sensefluid-flow

Intracellular signaling: Sonic Hedgehog signaling

A. Why cilia are important?

B. How they are formed?

Axoneme

Basal body

Plasma membrane

Transition zone

Ciliary membrane

Complex structure of a cilium

Ishikawa and Marshall, 2011Majumder and Fisk, Cell Cycle, 2013

Arl13B Acetylatedtubulin

Merge

Ciliarymembrane

Axoneme

A centrosome contains a pair ofcentrioles

Figure 16-31b: MolecularBiology of the Cell

Daughtercentriole

Mother centriole

Appendages

Figure 16-84b: MolecularBiology of the Cell

Triplet microtubules

(PCM)

Ultra-structure of centrioles

C. Rieder

Appendages

Mothercentriole

Daughtercentriole

Triplet Microtubules

M. Bornens

Figure 16-30a-b: MolecularBiology of the Cell

The centrosome is the majormicrotubule organizing center

Figure 16-31a: Molecular Biology of the Cell

γ-TuRC mediates microtubule nucleation

Reconstructed from EMof individual complexes

EM of a singlemicrotubulenucleatedfrom γ-TuRC

Figure 16-30c: MolecularBiology of the Cell

Reconstituted image of a centrosomefunctioning as MTOC

Centriole duplication cycle

Centrosomeseparation

Elongation andmaturation

Procentrioleformation

Centrioledisengagement

G1 S

G2M

MCDC

Centrosome separation afternew centrosome assembly

MicrotubulesCentrosomes

Human osteosarcoma U2OS cell

Shubhra Majumder

DNA

Centrosomes form the bipolarspindle

Microtubules Centrosomes

Mouse fibroblast NIH 3T3 cell

Harold FiskKinetochores

DNA

The cartwheel provides the baseto assemble a new centriole

Loncarek and Khodjacov, 2009

Cartwheel

Assembly ofcentriolar MTaround cartwheel

Elongation ofprocentriole Cartwheel

disappear aftercentriole maturation

The cartwheel provides thenine-fold symmetry

Gonczy, Nat Rev Mol Cell Biol. 2012

Electron micrograph of the proximalregion of a Chlamydomonas reinhardtiicentriole

A-C linker

A. Why cilia are important?

B. How are they formed?

Structural components of a cilium

Reiter et al. EMBO Rep. 2012

Structure of motile vs non-motile cilia

Reiter et al. EMBO Rep. 2012

Figure 16-81: MolecularBiology of the Cell

Arrangement of ciliary microtubules

A

B

Electron micrograph of the flagellum ofChlamydomonas reinhardtii

Dynein provides the ciliary motility

Figure 16-82: MolecularBiology of the Cell

Head

Stem

Base

Figure 16-83A: MolecularBiology of the Cell

Flagellar dynein produces sliding forceA B

Figure 16-83B: MolecularBiology of the Cell

Sliding force generates the bendingof axonemal microtubules

Figure 16-80: MolecularBiology of the Cell

Wave-like flagellary motion vs ciliary beating

Conservation of ciliary ultrastructure

Carvalho-Santos et al. J Cell Biol. 2011

The cartwheel provides the nine-foldsymmetry

Gonczy, Nat Rev Mol Cell Biol. 2012

Basal bodies are modified centrioles

Figure 16-84A: MolecularBiology of the Cell

Assembly of a cilium

Reiter et al. EMBO Rep. 2012

Golgi

Intraflagellar transport in cilia

Ishikawa and Marshall, 2011

IFT: A bi-directional movement of a largeprotein complex on microtubules

Motor activity of kinesin

Source: The lab website of Dr Ron Vale http://valelab.ucsf.edu/external/moviepages/moviesMolecMotors.html

Motor activity of cytoplasmic dynein

Carter, J Cell Sc. 2013

Walking of cytoplasmic dynein motor onmicrotubules

Intraflagellar transport in cilia

Total Internal Reflection Fluorescence (TIRF) microscopy of IFT20-GFPin Chlamydomonas flagellumEngel et al., Methods Cell Biol. 2009

Ciliary disassembly is coordinated with cellcycle to maintain centriole homeostasis

G0Primary cilia assembly

Disassembly

G1 S

G2M

MCDC

BB

Regulation of ciliary disassembly

Active mechanisms:

1. HDAC6 mediated deacetylation of axonemal microtubules

2. Depolymerization of the axonemal microtubules by kinesins

Pugacheva et al., Cell, 2007

Ciliopathies or cilia-related diseases

Motile cilia

Respiratory tract infection

Male infertility

Kartagener’s syndrome

Situs inversus (loss of left-right asymmetry)

Primary cilia

Polycystic kidney disease

Retinal dystrophy

Developmental defects in organs

Cancer