Schematic model of motility regulation in C. reinhardtii axonemes. (A and B) Models depicting mechanical/chemical signaling pathways (dotted red arrows) in C. reinhardtii axonemes. Transverse (A) and longitudinal (B) sections are shown. Based on genetic and pharmacological experiments, signals are transmitted from the CP, through the RS1 to I1 dynein, and through RS2 to the CSC and N-DRC. Signals are also thought to be transmitted from I1 dynein and N-DRC to ODAs through OIDLs (blue lines in B). The question addressed here is how signals are transmitted to I1 dynein (question marks in A and B).