Appearance of opsin-containing vesicles as rhabdomeric precursors and their incorporation into the rhabdom around dusk in the compound eye of the crab, Hemigrapsus sanguineus

This paper presents immunocytochemical, freeze-fracture, and fine-structura l evidence for the hypothesis that the precursors of the rhabdomeric membra nes are vesicles in the photoreceptors of the crab Hemigrapsus sanguineus. The number of vesicles starts to increase in the photoreceptor cell body at midday and peaks at approximately one hour before light-off. The vesicles move toward the rhabdom: they almost disappear from the cell body within th e first hour after light-off. As they move, the rhabdom area increases. Ele ctron microscopic immunocytochemistry and freeze-fracture EM revealed that the vesicles contain the visual pigment opsin as an integral membrane prote in. Based on detailed observation at the microvillar base by conventional e lectron microscopy, we present a model of how the vesicles are incorporated into the rhabdom to elongate the rhabdomeric microvilli.