An Efficient Screen for Cell-Intrinsic Factors Identifies the Chaperonin CCT and Multiple Conserved Mechanisms as Mediating Dendrite Morphogenesis

Abstract

Dendritic morphology is inextricably linked to neuronal function. Systematic large-scale screens combined with genetic mapping have uncovered several mechanisms underlying dendrite morphogenesis. However, a comprehensive overview of participating molecular mechanisms is still lacking. Here, we conducted an efficient clonal screen using a collection of mapped P-element insertions that were previously shown to cause lethality and eye defects in Drosophila melanogaster. Of 280 mutants, 52 exhibited dendritic defects. Further database analyses, complementation tests, and RNA interference validations verified 40 P-element insertion genes as being responsible for the dendritic defects. Twenty-eight mutants presented severe arbor reduction, and the remainder displayed other abnormalities. The intrinsic regulators encoded by the identified genes participate in multiple conserved mechanisms and pathways, including the protein folding machinery and the chaperonin-containing TCP-1 (CCT) complex that facilitates tubulin folding. Mutant neurons in which expression of CCT4 or CCT5 was depleted exhibited severely retarded dendrite growth. We show that CCT localizes in dendrites and is required for dendritic microtubule organization and tubulin stability, suggesting that CCT-mediated tubulin folding occurs locally within dendrites. Our study also reveals novel mechanisms underlying dendrite morphogenesis. For example, we show that Drosophila Nogo signaling is required for dendrite development and that Mummy and Wech also regulate dendrite morphogenesis, potentially via Dppand integrin-independent pathways. Our methodology represents an efficient strategy for identifying intrinsic dendrite regulators, and provides insights into the plethora of molecular mechanisms underlying dendrite morphogenesis.

PP2A phosphatase regulates cell-type specific cytoskeletal organization to drive dendritic diversification

“…The present study reveals that the PP2A phosphatase has a differential regulatory effect on dendritic morphology in different classes of Drosophila md neurons. Consistent with recent studies (Rui et al , 2020; Wolterhoff et al , 2020, Wang et al, 2020), we discovered that loss of catalytic subunit mts or scaffolding subunit PP2A-29B in CIV md neurons severely disrupt dendritic morphology. However, disruption of only one regulatory subunit, wdb, had a notable effect on larval dendritic morphology, suggesting Wdb functions as a key regulatory subunit in these neurons during larval dendritic development.…”

“…A recent study implicated the PP2A B’ regulatory subunit widerborst ( wdb ) in Drosophila md neuron dendrite development (Das et al , 2017), while two other studies reveal roles of the PP2A complex in regulating dendritic pruning in CIV md sensory neurons (Rui et al , 2020; Wolterhoff et al , 2020) and an additional study identified PP2A components in regulating CIV larval md neuron dendritogenesis (Wang et al, 2020), however the putative mechanistic role(s) of PP2A in regulating subtype-specific dendritic arborization during larval development remain largely unknown. To investigate the potential functional requirements of PP2A in this process, we first conducted IHC analyses which revealed that the catalytic subunit, Mts, is expressed in md neuron subclasses ( Fig S1A,A’ ).…”

NeuroSCORE: A Genome-wide Omics-Based Model to Identify Candidate Disease Genes of the Central Nervous System

“…Furthermore, within this region are four high scoring ( BCL11A, USP34, XPO1 , and CCT4 ), of which the CCT4 gene was not previously identified. Experimental work in Drosophila shows CCT4 knockdown results in severely reduced dendritic growth 78 , as well as abnormalities of the eye and other organs 77 ; furthermore, two de novo , missense variants have been reported in two individuals with ASD 18 . These data support a role for 2p15p16.1 gains in CNS phenotypes and indicate the CCT4 gene as a new candidate gene.…”

Fringe-positive Golgi outposts unite temporal Furin 2 convertase activity and spatial Delta signal to promote dendritic branch retraction

“…Concomitantly, Dl is expressed in epidermal cells, providing the spatial cue for activating N signaling to promote terminal branch retraction. We excluded the involvement of conventional N signaling mediated by the nuclear factor Su(H) (Figure S7C), which may instead be involved in dendritic patterning at earlier stages of C4da neuronal development (Wang et al, 2020). Our data suggest that non-canonical N signaling promotes branch retraction by regulating actin dynamics, likely via downstream effectors to modulate polymerization and branching of actin filaments, similar to regulating axonal extension in Drosophila (Kannan et al, 2018;Kuzina et al, 2011).…”