Mbnl2 knockouts had normal amounts, and natural diurnal distributions, of wakefulness and non-REM (NREM) sleep ( Figure 2A). Modest wake fragmentation during dark periods (frequent and shorter wake episodes) was also observed in the knockout mice ( Figure 2B). However, the most profound sleep phenotypes were an increase in REM sleep amounts, associated with increased numbers of REM sleep episodes ( Figures 2A and 2B) and increased EEG theta power (data not shown). This change was most notable during the dark period when mice are normally awake. Interestingly, a larger portion of these dark period

REM sleep episodes in Mbnl2 knockouts exhibited a short latency (<100 s) from the preceding wake episodes ( Figure 2C). The mean REM sleep latency of all observed episodes click here JAK assay for the knockouts (115.8 ± 5.4 s) was significantly shorter than that of wild-type mice (132.3 ± 8.7 s). No direct transition from wake to REM sleep, an EEG/EMG phenotype equivalent to behavioral cataplexy ( Fujiki et al., 2009), was seen in either wild-type or knockout mice. A change in REM sleep in Mbnl2 knockouts was also observed during rebound sleep after a 6 hr sleep deprivation period initiated at

zeitgeber time (ZT) 0, in which a more profound REM sleep rebound was observed in knockout, compared to wild-type, mice ( Figure 2D). These sleep changes were REM sleep specific, as no changes in wake and NREM sleep was seen in these knockout mice at the

baseline and during sleep rebound. Overall, these results indicate that Mbnl2 knockout mice exhibit increased REM sleep propensity and provide a valuable model to study the molecular basis of REM-associated Histamine H2 receptor sleep abnormalities in myotonic dystrophy. To address additional DM-linked phenotypes in Mbnl2 knockouts, we first mapped the spatial expression pattern of Mbnl2 in the brain using Mbnl2GT4 heterozygous mice and tagged allele-specific β-galactosidase expression. This analysis revealed Mbnl2 expression throughout the brain in both neurons and glia with prominent expression in neurons of the hippocampus, dentate gyrus, and cerebellar Purkinje cells ( Figures 3A and S2E). Mbnl2 localized predominantly to the nucleus in these neuronal populations, although in other regions of the brain, including the cerebral cortex, it was detectable in both the nucleus and cytoplasm ( Figures 3B and S2F). Mbnl1 is primarily cytoplasmic in some neuronal populations, such as Purkinje cells ( Daughters et al., 2009), but was detectable in hippocampal nuclei at a much lower level than Mbnl2 ( Figure S2G). Since Mbnl2 was prominently expressed in the hippocampus, a key region of the brain involved in learning and memory, we next examined whether Mbnl2 loss resulted in memory impairment as observed in DM patients.