Pkd1l1 complexes with Pkd2 on motile cilia and functions to establish the left-right axis

Abstract

SUMMARYThe internal organs of vertebrates show distinctive left-right asymmetry. Leftward extracellular fluid flow at the node (nodal flow), which is generated by the rotational movement of node cilia, is essential for left-right patterning in the mouse and other vertebrates. However, the identity of the pathways by which nodal flow is interpreted remains controversial as the molecular sensors of this process are unknown. In the current study, we show that the medaka left-right mutant abecobe (abc) is defective for left-right asymmetric expression of southpaw, lefty and charon, but not for nodal flow. We identify the abc gene as pkd1l1, the expression of which is confined to Kupffer's vesicle (KV, an organ equivalent to the node). Pkd1l1 can interact and interdependently colocalize with Pkd2 at the cilia in KV. We further demonstrate that all KV cilia contain Pkd1l1 and Pkd2 and left-right dynein, and that they are motile. These results suggest that Pkd1l1 and Pkd2 form a complex that functions as the nodal flow sensor in the motile cilia of the medaka KV. We propose a new model for the role of cilia in left-right patterning in which the KV cilia have a dual function: to generate nodal flow and to interpret it through Pkd1l1-Pkd2 complexes.

Pkd1l1 establishes left-right asymmetry and physically interacts with Pkd2

“…The requirement for Pkd2 genes in L-R patterning has been demonstrated in both mouse (Pennekamp et al, 2002) and zebrafish (Bisgrove et al, 2005;Schottenfeld et al, 2007), but in both cases the associated interacting partner has remained unidentified. Our work, and that of Kamura and colleagues studying these loci in the medaka fish (Kamura et al, 2011), both point to Pkd1l1 and Pkd2 acting together downstream of nodal flow to mediate L-R patterning, arguing that this is an evolutionarily conserved mechanism.…”

“…The presence of a Ca 2+ signal spreading from the left side of the node in all of these models raises the possibility that Pkd proteins might be involved downstream of flow detection. A third model is proposed by Kamura and colleagues (Kamura et al, 2011). Following extensive analysis, they do not detect immotile cilia in the medaka fish Kupffer's Vesicle (KV; equivalent to the mouse node), and therefore argue that motile KV cilia must act to detect either a morphogen gradient or flow-based stresses.…”

Fluid flow and interlinked feedback loops establish left–right asymmetric decay of Cerl2 mRNA

“…The absence of Cerl2 mRNA in the apical region of left crown cells in wild-type embryos as well as the accumulation of Cerl2 mRNA in this region in a mutant (iv/iv) lacking nodal flow suggest that the mRNA is degraded at the apical side of left crown cells in response to the flow. Given that the Ca 2 þ channels Pkd2 and Pkd1l1 are required for flow detection [22][23][24][25] , Ca 2 þ signalling may contribute to the degradation of Cerl2 mRNA. How does Wnt signalling regulate Cerl2 mRNA stability?…”

Loss of the Ciliary Kinase Nek8 Causes Left-Right Asymmetry Defects

“…19 Heterotaxy also occurs with loss of the Pkd1-related gene, Pkd1l1; the gene product localizes to cilia and interacts with PC2, forming a node-specific complex required for proper asymmetry. 23,24 Alternatively, mutations that disrupt cilia assembly and/or structure cause both phenomena. PKD arises in the kidneyspecific deletion of Kif3A, which encodes a kinesin subunit required for ciliogenesis, and in Tg737 (Ift88/polaris) hypomorphs that exhibit shorter cilia with bulbed tips.…”