Localization of a visual Gq protein in the photoreceptors of a polychaete, Perinereis brevicirris (Annelida)

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.

Ultrastructure and localization of a visual Gq protein in ied epitoke ocelli of Perinereis brevicirris (Polychaeta, Annelida)

“…The heterotrimeric G protein Gq is one of the essential molecules in the phototransduction cascade of rhabdomeral photoreceptors. We have previously localized the visual Gq protein in the rhabdomeric microvilli in the ocelli of the normal type of Perinereis by using anti-GqC antibody (Miyako-Shimazaki et al 1999). In the present study, the Fig.…”

“…We have previously reported that visual Gq protein is localized only in the photoreceptive membrane in the ocelli of normal individuals of Perinereis (Miyako-Shimazaki et al 1999). Here, we have studied the ultrastructural changes and localization of visual Gq protein in the epitoke ocelli, in which an anti-GqC antibody labels highly developed membranous structures associated with the photoreceptive membranes.…”

“…1). The retina of the ocelli is composed of at least two types of cells: pigmented supporting cell (PS) and photoreceptor cell (PR; Miyako-Shimazaki et al 1999). The outer pigmented layer contains PR and PS cell bodies, and the inner rhabdomeric layer consists of cytoplasmic processes from these two cell types.…”

“…Details of the antibody and the procedure for the post-embedding immunogold labeling were as described in Miyako-Shimazaki et al (1999). Briefly, anterior and posterior ocelli were dissected from the prostomium and fixed overnight at 4°C with 4% paraformaldehyde in 0.1 M sodium phosphate buffer pH 7.4 (PB) containing 0.4 M sucrose and 0.3% Tween 20.…”