3. Primary cilium sensing fluid-shear depends on mechanoproteins polycystins and structural polaris

#### 3.1. Intraflagellar transport

IFT is required for assembly and maintenance of cilia. Briefly, ciliogenesis is initiated in the apical cytoplasm at the basal body. Proteins involved in cilium formation concentrate and assemble into complexes that migrate along the cilia axonemal microtubules through a process called IFT. The anterograde movement of particles from the cell body to the tip of the flagella/cilia is driven by Sensing Fluid-Shear Stress in the Endothelial System with a Special Emphasis on the Primary Cilium http://dx.doi.org/10.5772/intechopen.73134 93

Figure 1. Scheme of the primary cilium. Longitudinal section showing the axoneme with the nine doublets of microtubules originating from the basal body. The right part of the figure shows transversal sections of motile and non-motile primary cilia. Note the absence of the central pair of microtubules and dynein arms in the primary cilium. Figure adapted with permission of [90].

kinesin II [26], whereas the retrograde movement from the tip back to the cell body is driven by cytoplasmic dynein [32]. The protein polaris is the gene product of the IFT particle 88 (ift88) that in mammalis is homologous to the gene Tg737. This protein is localized to the basal body [26, 33] and is required for ciliogenesis.
