Exocytotic shedding and glial uptake of photoreceptor membrane by a salticid spider

Abstract

Receptors in the anterior lateral eyes of salticid spiders possess paired rhabdomeres. The tips of the rhabdomeral microvilli lie adjacent to nonpigmented glial processes. Photoreceptor membrane is lost during turnover by a hitherto undescribed process: individual microvilli lengthen at their tips, taper and are received by corresponding, coated endocytotic pits in the glial membrane. Pits detach as coated vesicles with coherent fragments of microvilli within them, lose their coats and accumulate in the glial processes as disorderly membranous detritus. Some microvillus membrane disintegrates before local endocytosis, and appears to get into the glial arms distant from the parent rhabdomere by invaginations which are either endocytotic clefts or a tubulo-cisternal system, but whose precise nature is not clear. No photoreceptor membrane is lost by pinocytosis into the receptor cytoplasm. Analogies between the behavior of this system and the phagocytosis of shed vertebrate photoreceptor membrane are briefly discussed.