The Presynaptic Cell Determines the Number of Synapses in the Drosophila Optic Ganglia

Abstract

The role of the pre- and postsynaptic cells in determining the number of synapses has been investigated in retina mosaics of the gigas (gig) mutant of Drosophila. Mutant photoreceptors are two to three times larger than those of the wild type, while adjacent cells in the mosaic retina and the lamina are normal in size. Serial electron microscope reconstructions of mosaic lamina cartridges show that gig photoreceptors establish more synapses upon lamina neurons than the normal photoreceptors do. By contrast, the number of feedback synapses that lamina neurons make onto gig photoreceptors does not increase. The increment in the number of synapses correlates positively with the increment of presynaptic cell membrane, resulting in constancy of synapse density. The phototactic response of flies bearing a gig eye is abnormal, indicating that the extra synapses are functional.

Presynaptic Recordings fromDrosophila: Correlatin of Macroscopic and Single-Channel K+Currents

“…These included the use of mutations, such as gigas, which yield very large boutons (up to 13 m) (Canal et al, 1994), giant, and lethal(1) disk large (Woods and Bryant, 1991), as well as pharmacological treatments promoting cell fusion or polyploidy in primary cultures. In our hands, only the mutant ecd proved to be a reliable tool to gain access to larval type III peptidergic boutons.…”

At a PI3K crossroads: lessons from flies and rodents

“…Indeed, gigas genetic mosaics displayed larger sensory and motor neurons with more prominent axons and terminals, although no changes were observed in their numbers. Even more interesting, mutant photoreceptors and olfactory sensory neurons established two to three times more synapses on genetically normal interneurons of the lamina optic neuropile (Canal et al , 1994 ) and central olfactory sensory neurons, respectively (Acebes and Ferrus , 2001 ). In both sensory systems, this gigas-dependent synaptic increase had functional consequences, modifying the phototactic response and olfactory perception of the fl ies.…”

Age-Independent Synaptogenesis by Phosphoinositide 3 Kinase

“…Thus, it is justified to explore the role that molecular mechanisms controlling cell size might have on synaptogenesis. In Drosophila, mutations in the tuberous sclerosis complex 2 (TSC2) ortholog gigas lead to a twofold to threefold increase of synapses in sensory neurons (Canal et al, 1994;Acebes and Ferrus, 2001). TSC2 is a negative regulator of signaling pathways downstream of tyrosine kinase receptors (TKRs) that modulates phosphoinositide 3 kinase (PI3K) signaling (Marygold and Leevers, 2002;Inoki et al, 2003).…”