This confocal image depicts neurons that were derived from human stem cells and sparsely infected with lentivirus expressing EGFP (blue). Nuclei were labeled with DAPI (white), dendrites labeled with antibodies against MAP2 (red), and synapses labeled with antibodies against synapsin (green). These neurons were used to assess phenotypes resulting from a mutation in the synaptic organizing protein Neuroligin-4. For more information, see the article by Cast et al. (pages 392–407) Cover Image: Thomas P. Cast.