elevated KCl (21). Among these “neural activity–regulated” genes, c3orf58 (deleted in patient AU-3101) was robustly increased within 6 hours of membrane depolarization (Fig. 3A). c3orf58 contained several evolutionarily conserved binding sites for MEF2, CREB, and SRF (Fig. 3B), and depolarization-dependent transcription of c3orf58 was strongly inhibited by RNA interference (RNAi) knock-down of the MEF2 transcription factor (Fig. 3A), which suggests that c3orf58 may be a direct or indirect MEF2 target. We propose renaming this gene DIA1 (deleted in autism-1). In the same forward screen, transcription of PCDH10 (the gene closest to the second-largest, >300-kbp, homozygous deletion in patient AU-7001) (Fig. 2A) was strongly up-regulated in hippocampal neurons in response to membrane depolarization (Fig. 3C). Although PCDH10 was not greatly affected by MEF2 RNAi, PCDH10 was robustly induced by a MEF2-VP16 fusion protein, reaching 1.31 ± 0.09 fold-induction of transcription and 1.94 ± 0.23 fold-induction at 1 hour and 2.5 hours, respectively. This transcriptional activation also suggests strongly that PCDH10 is a transcriptional target of MEF2. Because the KCl depolarization assay identified fewer than 5% of the transcriptome as altered in expression, the identification in this assay of two of three genes associated with the two largest deletions is quite unlikely
