Neuroligin-4 Regulates Excitatory Synaptic Transmission in Human Neurons

The autism-associated synaptic-adhesion gene Neuroligin-4 (NLGN4) is poorly conserved evolutionarily, limiting conclusions from Nlgn4 mouse models for human cells. Here, we show that the cellular and subcellular expression of human and murine Neuroligin-4 differ, with human Neuroligin-4 primarily expressed in cerebral cortex and localized to excitatory synapses. Overexpression of NLGN4 in human neurons resulted in an increase in excitatory synapse numbers but a remarkable decrease in synaptic strength. Human neurons carrying the syndromic autism mutation NLGN4-R704C also formed more excitatory synapses but with increased functional synaptic transmission due to a postsynaptic mechanism, while genetic loss of NLGN4 did not significantly affect synapses in the human neurons analyzed. Thus, the NLGN4-R704C mutation represents a change of function mutation. Our work reveals contrasting roles of NLGN4 in human and mouse neurons, suggesting human evolution has impacted even fundamental cell biological processes generally assumed to be highly conserved. Overall design: We compared the global gene expression profiles of induced neuronal (iN) cells. iN cells were derived from human embryonic stem cells (H1) by expression of transcription factors. Ngn2 was used to generate Ngn2-iN, Alsc1 and Dlx2 to generate AD-iN cells and Alsc1 and Myt1l to generate AM iN cells. AM and Ngn2 iN cells are glutamatergic neurons whereas AD iN cells are GABAergic. Mature iN cells cultured with mouse glia (6 weeks after transgene induction) were dissociated with Trypsin and FACS-sorted in Trizol LS. To distinguish from glial cells, iN cells were transduced with a lentiviral vector expressing EGFP under the control of CAG promoter together with the reprogramming transcription factors.