Genomic loci adjacent to genes encoding for transcription factors and chromatin remodelers are enriched for long non-coding RNAs (lncRNAs), but the functional importance of this enrichment is largely unclear. Chromodomain helicase DNA binding protein 2 (Chd2) is a chromatin remodeller with various reported functions in cell differentiation and DNA damage response. Heterozygous mutations in human CHD2 have been implicated in epilepsy, neurodevelopmental delay, and intellectual disability. Here we show that Chaserr, a highly conserved lncRNA transcribed from a region near the transcription start site of Chd2 and on the same strand, acts in concert with the CHD2 protein to maintain proper Chd2 expression levels. Loss of Chaserr in mice leads to early postnatal lethality in homozygous mice, and severe growth retardation in heterozygotes. Mechanistically, loss of Chaserr leads to substantially increased Chd2 mRNA and protein levels, which in turn lead to increased transcriptional interference by inhibiting promoters found downstream of highly expressed genes. We further show that Chaserr production represses Chd2 expression solely in cis, and that the phenotypic consequences of Chaserr loss are rescued when Chd2 is perturbed as well.Targeting Chaserr is thus a potentially viable strategy for increasing CHD2 levels in haploinsufficient individuals. excluded in this model. A different model for Chd2 loss-of-function was recently created by the International Mouse Phenotyping Consortium, where exon 3 was replaced by a lacZ cassette and a stop signal 18 . No significant changes in mortality and aging were reported for these mice, but they exhibit slightly decreased body weight and length, skeletal abnormalities, an abnormal bone structure, decreased fat amount and bone mineral density, and abnormalities in blood composition, such as decreased erythrocyte cell number, hemoglobin content, and mean platelet volume (http://www.mousephenotype.org/).In humans, CHD2 haploinsufficiency is associated with neurodevelopmental delay, intellectual disability, epilepsy, and behavioral problems (reviewed in 19 ). Studies in mouse models and cell lines also implicate Chd2 in neuronal dysfunction: perturbations of Chd2 affect neurogenesis in the mouse developing cerebral cortex 20 and in human stem cells differentiated to neurons 21 , and loss of a single Chd2 copy leads to deficits in neuron proliferation and a shift in neuronal excitability 22 . Approaches for increasing CHD2 levels may thus have therapeutic relevance.
ResultsLncRNAs are spread throughout vertebrate genomes, but have a notable enrichment in proximity to chromatin-and transcription-related genes 2,9 . One such lncRNA, annotated as 1810026B05Rik in mouse (which we denote as Chaserr, for CHD2 adjacent, suppressive regulatory RNA) and LINC01578/LOC100507217 in human (CHASERR), is an almost completely uncharacterized lncRNA, found upstream of and transcribed from the same strand as Chd2 (Fig. 1a). Chaserr has five exons, is polyadenylated, and is a bona fide lncRNA according...