Adenylyl cyclase 9: fundamental change of regulation in vertebrates and gene sub-functionalization after teleost-specific whole-genome duplication

Adenosine 3:5 monophosphate (cAMP) is a ubiquitous signalling molecule generated by the adenylyl cyclase family of proteins which is encoded by ten genes. The biological significance of this diversity is not well understood. In mammals, transmembrane adenylyl cyclase 9 (AC9) is resistant to regulation by heterotrimeric G proteins. A major facet of this resistance is auto-inhibition -- in the presence of activated Gs, AC9 is inhibited by its C-terminal domain. Here, we examined the natural evolution of this seemingly paradoxical control mechanism. At the primary sequence level, the hallmarks of auto-inhibition are apparent in all vertebrates, none are found in invertebrates. Teleost-specific genome duplication (TGD) resulted in adcy9 ohnologs, one of which lacked the hallmarks of auto-inhibition. This was confirmed in functional assays upon cloning and heterologous expression of the requisite cDNAs. The tissue distributions of the adcy9 ohnologs in teleost species also pointed to their sub-functionalization. Above all, auto-inhibited adcy9 was largely restricted to the brain indicating a fundamental role in brain development or function. Our findings document a quantum leap of the regulation of the enzymatic activity of AC9 in vertebrates and the potency of TGD to meet an adaptational challenge through functionally diversified ohnologs.