ABSTRACT
Heterotrimeric GTP-binding proteins (G proteins) play an important role in phototransduction. The presence of G-protein subclasses has been reported in photoreceptive membranes, e.g., the Gi subgroup (transducin) in vertebrate rods, and the Gq subgroup in the eyes of the Arthropoda and the Mollusca. We examined the immunoreactivity and distribution of a Gq homologue in the cerebral ocelli of Perinereis brevicirris (Polychaeta, Annelida) using an anti-GqC antibody raised against a conserved sequence at the C-terminal of the alpha-subunit of Gq (Gq-alpha). The anti-GqC antibody labeled a 48-kDa band on the Western blot of proteins from the Perinereis ocelli. The anti-GtC antibody, which is raised against the C-terminal sequence of bovine transducin alpha-subunit (Gt-alpha), did not cross-react to the ocellar proteins of Perinereis. The rhabdomeric layers of the anterior and posterior ocelli were strongly labeled by anti-GqC on light-microscopic immunohistology. Immunoelectron microscopy showed that the Gq molecules were specifically localized in the photoreceptive membrane of the rhabdomeric microvilli. These results suggest that the Gq protein plays a role in the phototransduction of the Perinereis ocelli.
Subject(s)
GTP-Binding Proteins/analysis , Photoreceptor Cells, Invertebrate/cytology , Polychaeta/cytology , Amino Acid Sequence , Animals , Antibodies , Cattle , Immunohistochemistry , Microscopy, Immunoelectron , Molecular Sequence Data , Peptide Fragments/chemistry , Peptide Fragments/immunology , Photoreceptor Cells, Invertebrate/physiology , Photoreceptor Cells, Invertebrate/ultrastructure , Retinal Rod Photoreceptor Cells/physiology , VertebratesABSTRACT
This paper describes a combination of electrophysiological and anatomical techniques useful for characterizing sensory neurons in insects in our studies on the extraocular photoreceptors on the genitalia of the butterfly, Papilio xuthus. Genital photoreceptors were first electrophysiologically identified by recording photoreceptor spikes in response to light stimulation of the genitalia. The precise location and ultrastructure of these photoreceptors were then studied by light and electron microscopy. Both electrophysiological and anatomical techniques employed here were rather classical, but, as shown in this paper, they appear to be particularly useful for systems where intracellular penetration is difficult.
