Local endocytosis triggers dendritic thinning and pruning in Drosophila sensory neurons

Abstract

The refinement of neural circuits involves dendrite pruning, a process that removes inappropriate projections that are formed during development. In Drosophila sensory neurons, compartmentalized calcium (Ca 2 þ ) transients in dendrites act as spatiotemporal cues to trigger pruning, yet how neurons define the dendrites with Ca 2 þ transients remains elusive. Here we report that local elevation of endocytic activity contributes to defining dendrites that generate Ca 2 þ transients, triggering pruning. In vivo imaging of single dendrites reveals an increase of endocytosis in proximal dendrites that spatially and temporally correlates with dendrite thinning, an early step in pruning tightly coupled with compartmentalized Ca 2 þ transients. Two GTPases, Rab5 and dynamin, are required for both the increased endocytic activity and compartmentalized Ca 2 þ transients. Further genetic analyses suggest that local endocytosis in proximal dendrites functions cooperatively with global endocytosis-mediated protein degradation pathways to promote dendrite pruning.

Regulation of dendrite growth and maintenance by exocytosis

“…To more directly visualize sites of exocytosis and function, we utilized a pH-sensitive reporter ( pHluorin-CD4-tdTomato; referred to as pH-Tom) comprising pH-sensitive GFP (ecliptic pHluorin) fused to the N-terminus of a red fluorescent membrane marker (CD4-tdTomato) (Kanamori et al, 2015) (Fig. 6A).…”

“…The following lines were used: Gal4 221 (Grueber et al, 2003), ppk-Gal4 (Grueber et al, 2007), A58-Gal4 (Galko and Krasnow, 2004), ppk-Frt-stopFrt-Gal4 (Kanamori et al, 2013), UAS-pHluorin-CD4-tdTomato (Kanamori et al, 2015), E7-2-36 (Brewster and Bodmer, 1995), SOP-FLP (Shimono et al, 2014), UAS-myrEos (Pfeiffer et al, 2010), ppk-CD4-tdTomato, UAS-CD4-tdGFP and UAS-CD4-tdTomato (Han et al, 2011), UAS-shi.K44A (Moline et al, 1999), and UAS-Dicer-2 (Dietzl et al, 2007). Rop G27 and Rop A19 (Harrison et al, 1994), Sec5 E10 and Sec5 E13 (Murthy et al, 2003), Sec6…”

Adult Drosophila sensory neurons specify dendritic territories independently of dendritic contacts through the Wnt5–Drl signaling pathway

“…During metamorphosis, the larval dendritic arbors are completely replaced with adult-specific processes as a result of extensive pruning and subsequent regeneration of dendritic trees (Kuo et al 2005;Shimono et al 2009;Yasunaga et al 2010;Kanamori et al 2015). In this study, we investigated how adult C4da neurons rebuild the dendritic territory and found that, unlike the larval dendrites, adult C4da dendrites specify a dendritic boundary independently of dendritic contacts.…”

Mechanismen des Neuritischen Prunings

“…(Lee, 2009). Außerdem werden in proximalen Dendriten vermehrt endozytische Vesikel gebildet, die Membranmaterial von der Plasmamembran abziehen (Kanamori et al, 2015). Durch die Kombination von Zytoskelettabbau und Membranabzug wird der Dendrit an der Basis ausgedünnt und destabilisiert (Abb.…”

“…In ihnen kann man nun häufig räumlich und zeitlich begrenzte Kalziumströme beobachten, sogenannte transients. Das Auftreten dieser transients ist ein Indikator, dass der betreffende Dendrit demnächst im proximalen Bereich abbrechen wird (Kanamori et al, 2015), was ab etwa 6 h APF passiert. Zur selben Zeit kann man in den abgeschnürten Dendriten aktive Caspasen detektieren -Proteasen, die normalerweise den regulierten Zelltod auslösen (Williams, 2006).…”