cDNA Sequences Reveal mRNAs for Two Gα Signal Transducing Proteins from Larval Cilia

In planktonic larvae of the gastropod mollusk, Haliotis rufescens (red abalone), settlement behavior and subsequent metamorphosis are controlled by two convergent chemosensory pathways that report unique peptide and amino acid signals from the environment. The integration of signals from these two sensory pathways provides for variable amplification, or fine-tuning, of larval responsiveness to the inducers of settlement and metamorphosis. These pathways may be analogous to the neuronal and molecular mechanisms of facilitation and longterm potentiation characterized in other (adult) molluscan systems. Recently, the chemosensory receptors and signal transducers apparently belonging to the regulatory pathway (including a G protein and protein kinase C) have been identified in cilia purified from H. rufescens larvae. These elements retain their sequential receptor-dependent regulation in the isolated cilia in vitro. As a first step toward the molecular genetic dissection of the receptors, transducers, and the mechanisms of their control of settlement behavior and metamorphosis, we present evidence that the cilia purified from these larvae contain polyadenylated mRNA corresponding to unique signal transducers. Purification of this mRNA, enzymatic synthesis of the corresponding cDNAs, amplification by the polymerase chain reaction, cloning, and sequence analysis reveal that the ciliary mRNA includes sequences that apparently code for two G{alpha} signal transducing proteins. One of these is highly homologous to members of the Gq family, recently shown in other systems to control the activity of phospholipase C; the other is more closely related to Gi and Go. These results extend the tractability of the Haliotis system to analyses of cDNA and protein sequences of chemosensory elements from isolated cilia. This is the first time that mRNA has been purified from isolated cilia, and the corresponding cDNA synthesized and characterized.