Biomedical Engineering Reference
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in human airway epithelia [
1569
]. The BBS proteins operate in cilium formation
and function. They localize to the neighborhood of primary cilia, especially the
basal body, ciliary axoneme, and pericentriolar region. The proteic complex —
the BBSome — that contains 7 BBS proteins lodges in centrioles and primary
cilia. Proteins BBS2 and BBS4 reside in structures associated with motile cilia.
Although BBS proteins are not required for ciliogenesis, their loss causes structural
and functional defects in cilia, such as bulges filled with vesicles near the tips of cilia
as well as reduced ciliary beat frequency, possibly due to an impaired intraflagellar
transport complex.
Inositol Pentakisphosphate 2-Kinase
Inositol (1,3,4,5,6)-pentakisphosphate (IP
5
) 2-kinase (IPPK; a.k.a. IPK1) that gen-
erates inositol hexakisphosphate (IP
6
) intervenes in ciliary beating and length
maintenance [
1570
].
26
Enzyme IPPK abounds in centrosomes and basal bodies,
where it colocalizes with BBS4 and BBS8 proteins. It influences microtubule-based
transport. Inositol polyphosphates modulate protein activity and may contribute to
the intraflagellar transport complex. They may act as cofactors for a component
of intraflagellar transport complex, cilium, or basal body, thereby allowing for its
optimal activity.
12.6.2
Cilium Beats
Cilia from the set of ciliated cells form a coordinated beating cluster. Cilia
synchronously beat, thereby induces rythmic waves, which propels the mucus layer
with trapped particles and germs. The epithelial lining fluid thickness is slightly less
than the length of an extended cilium. The cilium tips thus can impact the superficial
mucus layer. The mucus is propelled by momentum transfer from the less viscous
liquid film. At the airway branching, ciliary motions impose a particle path lateral
from the apex.
12.6.2.1
Cilium Beating Stages
The beat cycle of respiratory cilia is composed of 3 phases [
1515
]: rest, recovery,
and effective stroke. In functionally intact frog palate epithelium, a resting state
26
Lipid-anchored phosphatidylinositol (4,5)-bisphosphate is the starting molecule for soluble
inositol polyphosphate production. Phospholipase-C produces diacylglycerol and soluble inositol
(1,4,5)-triphosphate. The latter is sequentially phosphorylated to produce inositol tetrakisphos-
phate, pentakisphosphate, and hexakisphosphate.
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