unfulfilledInteracting Genes Display Branch-Specific Roles in the Development of Mushroom Body Axons inDrosophila melanogaster

Abstract

The mushroom body (MB) of Drosophila melanogaster is an organized collection of interneurons that is required for learning and memory. Each of the three subtypes of MB neurons, γ, α´/β´, and α/β, branch at some point during their development, providing an excellent model in which to study the genetic regulation of axon branching. Given the sequential birth order and the unique patterning of MB neurons, it is likely that specific gene cascades are required for the different guidance events that form the characteristic lobes of the MB. The nuclear receptor UNFULFILLED (UNF), a transcription factor, is required for the differentiation of all MB neurons. We have developed and used a classical genetic suppressor screen that takes advantage of the fact that ectopic expression of unf causes lethality to identify candidate genes that act downstream of UNF. We hypothesized that reducing the copy number of unf-interacting genes will suppress the unf-induced lethality. We have identified 19 candidate genes that when mutated suppress the unf-induced lethality. To test whether candidate genes impact MB development, we performed a secondary phenotypic screen in which the morphologies of the MBs in animals heterozygous for unf and a specific candidate gene were analyzed. Medial MB lobes were thin, missing, or misguided dorsally in five double heterozygote combinations (;unf/+;axin/+, unf/+;Fps85D/+, ;unf/+;Tsc1/+, ;unf/+;Rheb/+, ;unf/+;msn/+). Dorsal MB lobes were missing in ;unf/+;DopR2/+ or misprojecting beyond the termination point in ;unf/+;Sytβ double heterozygotes. These data suggest that unf and unf-interacting genes play specific roles in axon development in a branch-specific manner.

The genetic basis of natural variation in mushroom body size in Drosophila melanogaster

“…These comprised 139 unique genes, as 18 genes were associated with two MB traits and four were associated with three mushroom body traits ( Supplementary Data 6 ). Six of the candidate genes are known to regulate MB development (starry night ( stan ), frizzled ( fz ), Protostome-specific GEF ( PsGEF ), Protein tyrosine phosphatase 10D ( Ptp10D ), misshapen ( msn ), vein ( vn )), four act in pathways that modulate MB development but have themselves never been linked to MB development (APP-like protein interacting protein 1 ( Aplip1 ), Ecdysone-induced protein 63E ( Eip63E ), Ecdysone-induced protein 75B ( Eip75B ), JIL-1 ) and two are involved in adult MB function (slowpoke ( slo ), pumilio ( pum )) 28 29 30 31 32 33 34 35 36 37 . No role in MB development or function has been reported for the remaining 127 genes.…”

“…Our GWA analyses identified many variants that are associated with variation in MB morphology, allowing us to identify genes and putative transcription factors involved in MB development. Of the 139 unique candidate genes, only eight have been previously reported to be involved in MB morphology or function 28 29 30 32 33 34 35 37 . Furthermore, more than one-third of the polymorphisms associated with variation in MB morphology were located in intergenic regions.…”

The making of the Drosophila mushroom body

“…Continued) Genes involved in the guidance and morphogenesis of KC axons. Gui (however,Yaniv et al suggest unf only has a role in γ axonal regrowth) βL-StopBates et al (2014),Bates et al (2010),Lin et al (2009),Yaniv et al (2012) Worpenberg et al (2021 AL-G: required for axonal guidance or extension for all KCs (based on gross lobe morphology). dL-G: required for guidance or extension of the dorsal lobes (based on gross lobe morphology).…”