Cyclic AMP signaling in bivalve molluscs: an overview

The cyclic AMP (cAMP)-dependent signaling accounts for the control of cellular cascades involved in many physiological functions, and a wealth of information is available on the cAMP system that operates in mammalian cells. Nevertheless, cAMP has a central role also in nonmammalian vertebrates and invertebrates. The present review aims at examining the information available on bivalve molluscs, from the first studies carried out in the early 1980s to the last progresses made in the present days. The major focus is on the structural and operational characteristics of the main actors of the signaling pathway, i.e., adenylyl cyclase, G proteins, and protein kinase A, and on the role played by the cyclic nucleotide on smooth muscle, heart, gills, gonads, and metabolism regulation. Moreover, recent evidence regarding the cAMP system as a target of environmental stress factors are discussed. It will become clear that cAMP does play a wide and important role in bivalve physiology. Several issues have been sufficiently clarified, although investigated only in a few model species. However, further fundamental aspects remain unknown, mainly regarding molecular features and interactions with other signaling pathways, thus requiring further elucidation.