number of pigment dispersing factor positive terminals. As seen in Social enrichment increases ppERK MedChemExpress 118414-82-7 levels Recent studies have shown that exposure to enriched environments can increase daytime sleep and synaptic morphology in the absence of sleep loss. Thus, we asked whether enriched social experience would alter ppERK levels. As seen in doi: 10.1371/journal.pone.0081554.t001 significant increase in ppERK levels relative to total ERK. Importantly, no changes in ppERK were observed when flies were exposed to 1) mechanical perturbation during the day, a manipulation that was designed to expose animals to the deprivation-stimulus without altering sleep homeostasis, 2) exposure to the toxin paraquat, or 3) starvation, a manipulation that is known to induce periods of waking without producing a sleep rebound or cognitive impairments . Consistent with 9030745 these results, sleep deprivation did not modify ppERK levels in hypomorphic rl1 mutant flies. Additionaly, Cs flies maintained in Dark:Dark and deprived of sleep for 12 hours show the same increase in ppERK levels as those on a 12:12 Light:Dark schedule. Together these data indicate that the increases in ppERK levels seen following sleep loss are not due to non-specific effects of stress or circadian effects. Previous studies have shown that sleep deprivation strongly up-regulates synaptic markers and is a potent modulator of synaptic morphology. Given the role of ERK in neuronal Nuclear localization of ERK regulates sleep and cAMP response element -mediated transcription ERK has been shown to play a role in synaptic plasticity by regulating protein synthesis at the level of translation initiation and/or by activating gene transcription. In order to 5 The Role of ERK in Sleep and 
Plasticity doi: 10.1371/journal.pone.0081554.g002 activate transcription, activated ERK translocates to the nucleus where it activates downstream transcription factors. To test if sleep deprivation increased levels of activated ERK in the nucleus, we performed western blots on nuclear fractions of fly heads exposed to sleep deprivation for 12 hours. We found that 12 hours of sleep deprivation resulted in an increase in 6 The Role of ERK in Sleep 22451932 and Plasticity doi: 10.1371/journal.pone.0081554.g003 ppERK activation in the nucleus. To further test the hypothesis that ERK activation in the nucleus is required for the behavioral phenotype we conducted experiments to block ERK translocation to the nucleus. When p90 ribosomal S6 kinase is co-expressed with UAS-ERKSEM, ERK is retained in the cytoplasm preventing its nuclear translocation and the activation of downstream targets. Thus, to determine whether the effects of ppERK are mediated though downstream nuclear events, we expressed UAS-RSKwt panneuronally in adult flies using Gsw-elav GAL4. As seen in in SL327 fed flies. These data suggest that activated ERK may be exerting its effects on sleep and plasticity, in part, by nuclear localization and activating gene transcription. To further explore this possibility we examined the ability of UAS-ERKSEM to activate cAMP response Element -binding protein -mediated transcription using transgenic flies carrying a CRE-Luc reporter. As seen in 7 The Role of ERK in Sleep and Plasticity doi: 10.1371/journal.pone.0081554.g004 8 The Role of ERK in Sleep and Plasticity doi: 10.1371/journal.pone.0081554.g005 9 The Role of ERK in Sleep and Plasticity Together these data suggest that nuclear localization of ppERK is sufficient to alter ge
