A putative tyrosine phosphorylation site of the cell surface receptor Golden goal is involved in synaptic layer selection in the visual system

Abstract

SUMMARYGolden goal (Gogo) is a cell surface protein that is crucial for proper synaptic layer targeting of photoreceptors (R cells) in the Drosophila visual system. In collaboration with the seven-transmembrane cadherin Flamingo (Fmi), Gogo mediates both temporary and final layer targeting of R-cell axons through its cytoplasmic activity. However, it is not known how Gogo activity is regulated. Here, we show that a conserved Tyr-Tyr-Asp (YYD) tripeptide motif in the Gogo cytoplasmic domain is required for photoreceptor axon targeting. Deleting the YYD motif is sufficient to abolish Gogo function. We demonstrate that the YYD motif is a phosphorylation site and that mutations in the YYD tripeptide impair synaptic layer targeting. Gogo phosphorylation results in axon stopping at the temporary targeting layer, and dephosphorylation is crucial for final layer targeting in collaboration with Fmi. Therefore, both temporary and final layer targeting strongly depend on the Gogo phosphorylation status. Drosophila Insulin-like receptor (DInR) has been reported to regulate the wiring of photoreceptors. We show that insulin signaling is a positive regulator, directly or indirectly, of YYD motif phosphorylation. Our findings indicate a novel mechanism for the regulation of Gogo activity by insulin signaling-mediated phosphorylation. We propose the model that a constant phosphorylation signal is antagonized by a presumably temporal dephosphorylation signal, which creates a permissive signal that controls developmental timing in axon targeting.

Glial insulin regulates cooperative or antagonistic Golden goal/Flamingo interactions during photoreceptor axon navigation

“…UAS-GogoΔC, <gogo<, <fmiN<, fmi[E59], UAS-Fmi, UAS-Fmi ΔC ; UAS-GogoFL-P40, UAS-GogoFFD-P40, UAS-GogoDDD-P40, GMR-GogoFFD-myc, GMR-gogoDDD-myc (Mann et al, 2012); UAS-add1-myc, hts[null], (Ohler et al, 2011); sens-lexA, LexAop-myrTomato, bshM-Gal4, UAS-myrGFP (Trush et al, 2019); GMR-Rho1 (Hariharan et al 1995); dilp7-Gal4 (Yang et al, 2008); dlip4-Gal4 is a gift from Dr.…”

“…Previous studies suggest that the cytoplasmic domain of Gogo is important for Gogo/Fmi collaborative functions, while they interact in cis Tomasi et al, 2008). It has also been shown that the YYD tripeptide motif in the cytoplasmic domain is required for Gogo function (Mann et al, 2012). Furthermore, Tyr1019…”

“…and Tyr1020 are known as the true phosphorylation sites in vivo (Mann et al, 2012). To test whether Gogo phosphorylation regulation is required during step 1, the Gogo phosphomimetic form (GogoDDD), nonphosphomimetic form (GogoFFD) and deletion of the entire cytoplasmic domain (GogoΔC) were used to rescue the gogo mutant phenotype.…”

Cadherin complexity: recent insights into cadherin superfamily function in C. elegans

“…The intracellular domain of FMI-1 is necessary for PVP pathfinding but dispensable for PVQ and HSN fasciculation [50••], suggesting that FMI-1 may have signaling activity necessary for pioneer axon guidance. Drosophila Flamingo can mediate neuronal morphogenesis through both Planar Cell Polarity (PCP) pathway-dependent and PCP-independent mechanisms [53–55]. However, there is currently no clear evidence for a full PCP pathway in C. elegans , and FMI-1 does not appear to function in a PCP-like pathway [50••,56].…”

Analysis of the Transcriptomes Downstream of Eyeless and the Hedgehog, Decapentaplegic and Notch Signaling Pathways in Drosophila melanogaster

“…A subset of the genes in the “neuronal differentiation” clusters is listed in Table S6. Some have known roles in photoreceptor differentiation, for instance in photoreceptor axon guidance, including the cell surface protein encoded by golden goal ( gogo ) [116], [117], [118], the low density lipoprotein (LDL) receptor repeat-containing protein encoded by jelly belly ( jeb ) [119], and the ARID/BRIGHT-family transcription factor retained/dead ringer ( retn ) [120], [121]. Also included in these clusters are genes with known roles in neuronal morphogenesis that have not previously been shown to have roles in photoreceptor morphogenesis.…”