Adenylyl cyclase (AC) is a key enzyme that synthesizes cyclic AMP (cAMP) at the 
onset of the signaling pathway to activate sperm motility. Here, we showed that 
both transmembrane AC (tmAC) and soluble AC (sAC) are distinctly involved in the 
regulation of sperm motility in the ascidian Ciona intestinalis. A tmAC 
inhibitor blocked both cAMP synthesis and the activation of sperm motility 
induced by the egg factor sperm activating and attracting factor (SAAF), as well 
as those induced by theophylline, an inhibitor of phoshodiesterase. It also 
significantly inhibited cAMP-dependent phosphorylation of a set of proteins at 
motility activation. On the other hand, a sAC inhibitor does not affect on 
SAAF-induced transient increase of cAMP, motility activation or protein 
phosphorylation, but it reduced swimming velocity to half in 
theophylline-induced sperm. A sAC inhibitor KH-7 induced circular swimming 
trajectory with smaller diameter and significantly suppressed chemotaxis of 
sperm to SAAF. These results suggest that tmAC is involved in the basic 
mechanism for motility activation through cAMP-dependent protein 
phosphorylation, whereas sAC plays distinct roles in increase of flagellar beat 
frequency and in the Ca2+-dependent chemotactic movement of sperm.