Cilia and ciliopathies Flashcards
What are the two classes of cilia?
Motile and primary cilia. They have similar structures, but generally different roles which sometimes over lap (i.e., motile cilia also have sensory roles).
Where are motile cilia found?
In the lungs and reparatory tract, as well as the female genitals. They function to propel mucous or ovum in one direction.
What do primary cilia do?
They function as “antenna” to detect and transmit signals into the cell.
Where are cilia found?
Lung, sinuses, eyes (rods are modified cilia), ears
What are cilia constructed of?
Two primary parts: a cytoskeletal elements and a sheath. The anchor or basal body is the centrosome of the cell, microtubules from the basal body are arranged in an axoneme, approx 1000 proteins all together.
What is the critical structure of the cilia?
The arrangment of microtubules. Triplets of microtubules lead out from the basal bodies, but transition to doublets in the cilia themselves. The first (a) micotubules are fully round and consist of 13 proteins in a circle, but the second and third MTs in the doublets (ab) or triplets (abc) link onto each other and do not form complete circles.
What is the sturctural difference between the motile and primary cilia?
The motile cilia have a 9 + 2 structure of 9 MT doublets in a circle around two singlet MTs. They also have outer dyneine arms that can grab onto the outer doublet structures and cause movement, along with internal radial spokes that regulate the movement. The primary cilia only have the outer ring of 9 doublets.
What functions does the transition zone serve?
Transition zone structures come off of the basal body and the ciliary axoneme and bind the basal body to the plasma membrane. They serve as a gate keeper limiting the components that can be transfered into or out of the cilia. This creates a unique domain that has its own membrane proteins and “cilioplasm” (as opposed to cytoplasm). Many ciolopathic mutations occur in the transition zone.
What is the basic structure of the ciliary membrane?
The ciliary membrane is continuous with the plasma membrane of the cell, but the transition zone structure provides a diffusion barrier that allows them to have specialized receptor proteins and other processes.
Where are lipid rafts found in the cilia?
They are trasported along the MTs by dyneine and kinesin motors and help to build the membrane of the cilia, as well as implant the membrane proteins that must exist in the cilia membrane.
Why and how do centrosomes duplicate during the cell cycle?
Centrosome duplication must occur in order to build future cilia. During G1, there are a pair of centrosomes present which then spawn the creation of daughter centrosomes orthogonally at their base. The mother centriole is the one that defines the site on new ciliogenesis. There are always 1 mother and 1 daughter centrosomes present, and both spawn daughter centrosomes during the cell cycle. After division the previous daughter centrosome becomes the mother centrosome and determines cilia formation.
How and where are cilia formed?
Cilia form from the mother centrosome (centriole) binding with ciliary vesicles from the golgi apparatus which then extend out with the creation of MTs. This all occurs in the cytoplasm. The axoneme structure is not constructed until the cilia is inserted into the membrane.
How are centrosomes formed in multiciliated cells?
Terminally differentiated cell may sprout hundreds of cilia, each of which needs a basal body. the centrosomes are replicated using the mother centriole or by a second structure called the deutersome that mimics the mother centriole and spits out lots of centrosomes as well. Deutersome is the primary source of basal bodies in multiciliated cells.
How do signaling cilia improve concentration of the signal?
They allow the concentration of specialized receptors such as light receptors in the rods, physical stimuli (temperature, gravity, strain, osmolality), or chemical signals (hormones, growth factors, morphogens). This information leads to a range of cell reactions: Cell proliferation, motility, polarity, growth, differentiation, tissue maintenance.
How does hedgehog (Hh) signaling function and what role does it play in development?
The Hh hormone binds to a receptor in the cilia which is then tranported out of the cilia into the plasma membrane, causing a signalin cascade through the cilia. Hh functions in morphologic control, covering finger development, bone growth, and brain development.
