At eclosion, Pectomb593 mutant photoreceptor cells in mosaic individuals show normal axon terminal morphology, as well as normal cell body morphology and arrangement in the retina; over the first 5 days of adult life, however, signs of cell body and axon terminal degeneration start to show, as axon terminals develop irregular, swollen morphologies, optic cartridges become incomplete and synaptic vesicles are reduced (CSP staining as proxy). All defects except the reduced synaptic vesicles are nearly absent when individuals are reared in the dark.
At 8h post eclosion, Pectomb593 mutant photoreceptor cells show normal cartridge organization, with only a modest increase in the variance in the number of R1-R6 photoreceptor terminals relative to controls; within each cartridge, the number of presynaptic release sites at T-bar ribbons is the same as in controls. Although individual photoreceptor axon terminals show normal size, they show fewer synaptic vesicles that are evenly spaced and distributed in small clusters, they show a severe increase in the number of dense-core vesicles, and show an increase in the number of shallow profiles of capitate projection organelles.
At 5 days of age, Pectomb593 mutant R1-R6 photoreceptor cell clones show signs of severe cell body and axon terminal degeneration, including electron-dense cytoplasm, loss of vesicles, capitate projections and synaptic T-bar ribbons; there is also the presence of endoplasmic reticulum-like structures. The retinas of 5-day-old adults also undergo degeneration, displaying both electron-dense cytoplasm and loss of rhabdomere structure.