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

Abstract

Functional ultrastructural changes in the rhabdomeric photoreceptors of the cerebral ocelli are described for normal and sexually mature (epitoke) Perinereis brevicirris (Polychaeta, Annelida). With sexual maturation, the cerebral ocelli hypertrophied, increasing in volume to 5.5 times that of ocelli in the normal state, and the thickness of the retinal layer increased up to 10 times. Perinereis ocelli have a pigmented retinal layer consisting of at least two cell types: photoreceptor cell (PR) and pigmented supporting cells (PS). In epitoke ocelli, PR bear well-developed rhabdomeric microvilli, multilamellar bodies, and numerous cytoplasmic membranous structures, including vesicles, smooth endoplasmic reticulum, and secondary lysosomes. Localization of a visual Gq protein in the ocelli was studied with anti-GqC antibody. The antibody strongly labeled not only microvilli and multilamellar bodies throughout the retinal layer, but also secondary lysosomes and vesicles in the cytoplasm of the PR in the epitoke ocelli, although labeling was observed only in the microvilli and multilamellar bodies in normal ocelli. Reverse transcription/polymerase chain reaction analysis revealed that the amount of G protein alpha subunit mRNA in the epitoke head increased by roughly twice that of the normal head. Since Gq protein is essential for phototransduction in Perinereis ocelli, these results suggest that the sites are involved in photoreceptive membrane turnover, which occurs much more extensively in epitoke ocelli. Thus, epitoke ocelli may represent a model system for studying rhabdomeric photoreceptive membrane turnover.

Two-year survey of Alitta succinea (Annelida: Nereididae) in fouling communities with notes on morphology and reproduction

“…The area of an epitoke's eyes is roughly double that of a similar sized atoke. This increase in gross anatomy likely occurs due to the elongation of the rhabdomeric layer within the eyes (Miyako-Shimazaki et al, 2005). Although these individuals' eye area increases, no studies have been conducted to determine if their field of view also increases.…”

“…Both pairs of eyes then experience hypertrophy. Although the exact anatomical mechanics of eye transmutations in A. succinea have not been documented, the ultrastructure of a closely related species, Perinereis brevicirris (Grube, 1847), has been compared in atoke and epitoke stages, showing a 10-fold increase in the width of the inner rhabdomeric layer (Miyako-Shimazaki et al, 2005). This increase in size is the result of an extension of their photoreceptor processes through photoreceptor membrane synthesis (Miyako-Shimazaki et al, 2005).…”