Table 3.

Microglial genes shown to affect synapses and behavior.

	Protein manipulated	KO type	Reported effects	Publications
Transmembrane proteins	DAP12	Constitutive	Reduced startle reflex to acoustic stimuli and reduced pre-pulse inhibition; Defective mIPSCs; impaired AMPA receptor accumulation: reduction in TrkB receptors; defective synaptic transmission; defective positioning of Lh6-expressing interneurons in cortical plate of E18.5	Kaifu et al., 2003; Roumier et al., 2004; Squarzoni et al., 2014
	CX3CR1	Constitutive	Defective positioning of Lh6-expressing interneurons in cortical plate of E18.5; increased cell death in cortical layer V; delayed maturation of synapses in barrel cortex; defective synaptic pruning and long-lasting impairments in social behavior and brain connectivity	Ragozzino et al., 2006; Maggi et al., 2011; Paolicelli et al., 2011; Rogers et al., 2011; Ueno et al., 2013; Squarzoni et al., 2014; Zhan et al., 2014
Complement	C1q	Constitutive	Enhanced connectivity and epilepsy	Chu et al., 2010
	C3 or CR3	Constitutive	Decreased synaptic engulfment	Schafer et al., 2012
Trophic factors	BDNF	Inducible conditional KO in CX3CR1-expressing cells	Altered synaptic protein levels; impaired spine formation and elimination; lack of training-induced improvement in motor behavior performance	Parkhurst et al., 2013
Phagocytosis and autophagy-related proteins	Progranulin	Constitutive	Increased synaptic pruning of C1q-tagged synapses	Lui et al., 2016
	ATG7 (autophagy related gene 7)	Conditional in lyzsozyme M-expressing cells	Increased dendritic spines; increased synaptic markers; long-lasting effects in sociability and repetitive behaviors	Kim et al., 2016

The table summarizes the main genetic factors that have been shown to affect neuronal circuits and behavior via microglia. The reader should consult Section “Genetic Factors Modulating Microglial Activity” for details and discussion.