Loss of Drosophila melanogaster p21-activated kinase 3 Suppresses Defects in Synapse Structure and Function Caused by spastin Mutations

Abstract

Microtubules are dynamic structures that must elongate, disassemble, and be cleaved into smaller pieces for proper neuronal development and function. The AAA ATPase Spastin severs microtubules along their lengths and is thought to regulate the balance between long, stable filaments and shorter fragments that seed extension or are transported. In both Drosophila and humans, loss of Spastin function results in reduction of synaptic connections and disabling motor defects. To gain insight into how spastin is regulated, we screened the Drosophila melanogaster genome for deletions that modify a spastin overexpression phenotype, eye size reduction. One suppressor region deleted p21-activated kinase 3 (pak3), which encodes a member of the Pak family of actin-regulatory enzymes, but whose in vivo function is unknown. We show that pak3 mutants have only mild synaptic defects at the larval neuromuscular junction, but exhibit a potent genetic interaction with spastin mutations. Aberrant bouton morphology, microtubule distribution, and synaptic transmission caused by spastin loss of function are all restored to wild type when pak3 is simultaneously reduced. Neuronal overexpression of pak3 induces actin-rich thin projections, suggesting that it functions in vivo to promote filopodia during presynaptic terminal arborization. pak3 therefore regulates synapse development in vivo, and when mutated, suppresses the synaptic defects that result from spastin loss.

The effects of ER morphology on synaptic structure and function in Drosophila melanogaster

“…Impaired evoked transmitter release in atl 2 and Rtnl1 1 null mutants Altered levels of several HSP proteins, including Spartin and Spastin, alter transmitter release from Drosophila motor nerve terminals (Nahm et al, 2013;Ozdowski et al, 2011;Sherwood et al, 2004). We tested the possibility that atl 2 and Rtnl1 1 might similarly affect transmitter release.…”

“…endosomes (Nahm et al, 2013;O'Connor-Giles et al, 2008;Ozdowski et al, 2011;Sherwood et al, 2004;Sweeney and Davis, 2002;Wang et al, 2007). The possible involvement of the ER in this receptor trafficking pathway will be discussed.…”

“…Mutants in Drosophila orthologs of several HSP genes, including spartin, spastin and spichthyin, and the additional related genes spinster and nervous wreck share a common set of nervous system phenotypes, including increased arborization and BMP signaling at the larval NMJ, decreased evoked transmitter release and locomotor deficits (Nahm et al, 2013;O'Connor-Giles et al, 2008;Ozdowski et al, 2011;Sherwood et al, 2004;Sweeney and Davis, 2002;Wang et al, 2007) (note that not all phenotypes have been reported for each mutant). The encoded proteins localize to various compartments within the endocytic receptor trafficking pathway (Allison et al, 2013;Edwards et al, 2009;O'Connor-Giles et al, 2008;Sweeney and Davis, 2002;Wang et al, 2007).…”

“…In Drosophila, loss of spastin, spartin and spichthyin confers a similar, but not identical, set of phenotypes including stabilized microtubules, increased synaptic bouton number and decreased evoked transmitter release at the larval neuromuscular junction (NMJ), age-dependent locomotor deficits and increased BMP signaling at the larval NMJ (Nahm et al, 2013;Ozdowski et al, 2011;Sherwood et al, 2004;Wang et al, 2007). These shared phenotypes might reflect disruption of a common pathway in endocytic receptor trafficking in these mutants.…”

Microtubule-severing protein Katanin regulates neuromuscular junction development and dendritic elaboration in Drosophila

“…Previous studies have uncovered an important role for spastin in neuromuscular junction (NMJ) growth and dendritic elaboration (Jinushi-Nakao et al, 2007;Ozdowski et al, 2011;Trotta et al, 2004;Sherwood et al, 2004;Yao et al, 2011;Ye et al, 2011). However, how katanin affects neuronal development has not been characterized at an organism level.…”