Tubulin Polymerization Promoting Protein, Ringmaker, and MAP1B Homolog Futsch Coordinate Microtubule Organization and Synaptic Growth

Abstract

Drosophila Ringmaker (Ringer) is homologous to the human T ubulin P olymerization P romoting P roteins (TPPPs) that are implicated in the stabilization and bundling of microtubules (MTs) that are particularly important for neurons and are also implicated in synaptic organization and plasticity. No in vivo functional data exist that have addressed the role of TPPP in synapse organization in any system. Here, we present the phenotypic and functional characterization of ringer mutants during Drosophila larval neuromuscular junction (NMJ) synaptic development. ringer mutants show reduced synaptic growth and transmission and display phenotypic similarities and genetic interactions with the Drosophila homolog of vertebrate M icrotubule A ssociated P rotein (MAP)1B, futsch. Immunohistochemical and biochemical analyses show that individual and combined loss of Ringer and Futsch cause a significant reduction in MT loops at the NMJs and reduced acetylated-tubulin levels. Presynaptic over-expression of Ringer and Futsch causes elevated levels of acetylated-tubulin and significant increase in NMJ MT loops. These results indicate that Ringer and Futsch regulate synaptic MT organization in addition to synaptic growth. Together our findings may inform studies on the close mammalian homolog, TPPP, and provide insights into the role of MTs and associated proteins in synapse growth and organization.

Acetylated α-tubulin residue K394 regulates microtubule stability to shape the growth of axon terminals

“…In control animals, elevating Futsch levels increased both the number of Futsch loops and type Ib boutons (Fig. 3, E and F), consistent with previous reports that increasing Futsch levels and microtubule stability stimulates type Ib bouton formation (Shi et al, 2019;Roos et al, 2000;Nechipurenko and Broihier, 2012). The over-expression of Futsch in K394R mutant neurons rescued Futsch loop formation, restoring loop numbers to normal, and also suppressed the formation of extra boutons (Fig.…”

Natural selection on sleep duration in Drosophila melanogaster

“…The seven polymorphisms with the lowest loglikelihoods in the short sleeper replicate 1 population (i.e., the lowest 5%) include four intergenic polymorphisms. www.nature.com/scientificreports/ it regulates microtubule formation necessary for proper organization and growth of the synapses at the larval neuromuscular junction 69 . Fkbp14 reduces Notch signaling 70 , which in turn can affect the response to sleep loss 71 .…”

Motor neuron boutons remodel through membrane blebbing

“…Instead it was observed that new boutons emerge from the presynaptic arbor by budding off round varicosities of membrane 27 . These studies also revealed that, in addition to microtubule remodeling [28][29][30][31][32][33][34] , new bouton growth induced by elevated activity is associated with actin cytoskeleton dynamics 27,[35][36][37] and requires proteins that regulate synaptic vesiclemachinery [38][39][40] suggesting that neuronal remodeling is likely coupled to synaptic transmission. Additionally, several signaling pathways have been shown to be implicated in the causal relationship between synaptic activity and bouton formation suggesting that activity-dependent plasticity at the NMJ results from a complex sequence of factors that are involved in the communication between MNs, muscle and glial cells 25 .…”