Genetic studies of memory formation in Drosophila have revealed that the formation of a protein synthesis-dependent long-term memory (LTM) requires multiple training sessions. LTM is blocked specifically by induced expression of a repressor isoform of the cAMP-responsive element-binding protein (CREB). Here, we report an enhancement of LTM formation after induced expression of an activator isoform of dCREB2. Maximum LTM is achieved after one training session, and its formation depends on phosphorylation of the activator transgene. A model of LTM formation based on differential regulation of CREB isoforms is proposed.

How long-term memories are stored is a fundamental question in neuroscience. The first molecular mechanism for long-term memory storage in the brain was recently identified as the persistent action of protein kinase Mzeta (PKMζ), an autonomously active atypical protein kinase C (PKC) isoform critical for the maintenance of long-term potentiation (LTP). PKMζ maintains aversively conditioned associations, but what general form of information the kinase encodes in the brain is unknown. We first confirmed the specificity of the action of zeta inhibitory peptide (ZIP) by disrupting long-term memory for active place avoidance with chelerythrine, a second inhibitor of PKMζ activity. We then examined, using ZIP, the effect of PKMζ inhibition in dorsal hippocampus (DH) and basolateral amygdala (BLA) on retention of 1-d-old information acquired in the radial arm maze, water maze, inhibitory avoidance, and contextual and cued fear conditioning paradigms. In the DH, PKMζ inhibition selectively disrupted retention of information for spatial reference, but not spatial working memory in the radial arm maze, and precise, but not coarse spatial information in the water maze. Thus retention of accurate spatial, but not procedural and contextual information required PKMζ activity. Similarly, PKMζ inhibition in the hippocampus did not affect contextual information after fear conditioning. In contrast, PKMζ inhibition in the BLA impaired retention of classical conditioned stimulus–unconditioned stimulus (CS-US) associations for both contextual and auditory fear, as well as instrumentally conditioned inhibitory avoidance. PKMζ inhibition had no effect on postshock freezing, indicating fear expression mediated by the BLA remained intact. Thus, persistent PKMζ activity is a general mechanism for both appetitively and aversively motivated retention of specific, accurate learned information, but is not required for processing contextual, imprecise, or procedural information.

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We show that atypical PKCiota, which plays a critical role in the establishment and maintenance of epithelial cell polarity, is genomically amplified and overexpressed in serous epithelial ovarian cancers. Furthermore, PKCiota protein is markedly increased or mislocalized in all serous ovarian cancers. An increased PKCiota DNA copy number is associated with decreased progression-free survival in serous epithelial ovarian cancers. In a Drosophila in vivo epithelial tissue model, overexpression of persistently active atypical PKC results in defects in apical-basal polarity, increased Cyclin E protein expression, and increased proliferation. Similar to the Drosophila model, increased PKCiota proteins levels are associated with increased Cyclin E protein expression and proliferation in ovarian cancers. In nonserous ovarian cancers, increased PKCiota protein levels, particularly in the presence of Cyclin E, are associated with markedly decreased overall survival. These results implicate PKCiota as a potential oncogene in ovarian cancer regulating epithelial cell polarity and proliferation and suggest that PKCiota is a novel target for therapy.

There has been considerable progress in elucidating the molecular mechanisms that contribute to memory formation and the generation of circadian rhythms. However, it is not well understood how these two processes interact to generate long-term memory. Recent studies in both vertebrate and invertebrate models have shown time-of-day effects on neurophysiology and memory formation, and have revealed a possible role for cycling molecules in memory persistence. Together, these studies suggest that common mechanisms underlie circadian rhythmicity and long-term memory formation.

In the fruit fly, Drosophila melanogaster, rest shares features with mammalian sleep, including prolonged immobility, decreased sensory responsiveness and a homeostatic rebound after deprivation. To understand the molecular regulation of sleep-like rest, we investigated the involvement of a candidate gene, cAMP response-element binding protein (CREB). The duration of rest was inversely related to cAMP signaling and CREB activity. Acutely blocking CREB activity in transgenic flies did not affect the clock, but increased rest rebound. CREB mutants also had a prolonged and increased homeostatic rebound. In wild types, in vivo CREB activity increased after rest deprivation and remained elevated for a 72-hour recovery period. These data indicate that cAMP signaling has a non-circadian role in waking and rest homeostasis in Drosophila.

Understanding how the brain captures transient experience and converts it into long lasting changes in neural circuits requires the identification and investigation of the specific ensembles of neurons that are responsible for the encoding of each experience. We have developed a Robust Activity Marking (RAM) system that allows for the identification and interrogation of ensembles of neurons. The RAM system provides unprecedented high sensitivity and selectivity through the use of an optimized synthetic activity-regulated promoter that is strongly induced by neuronal activity and a modified Tet-Off system that achieves improved temporal control. Due to its compact design, RAM can be packaged into a single adeno-associated virus (AAV), providing great versatility and ease of use, including application to mice, rats, flies, and potentially many other species. Cre-dependent RAM, CRAM, allows for the study of active ensembles of a specific cell type and anatomical connectivity, further expanding the RAM system’s versatility.DOI: http://dx.doi.org/10.7554/eLife.13918.001

SUMMARY NMDA receptor (NMDAR) channels allow Ca2+ influx only during correlated activation of both pre- and postsynaptic cells; a Mg2+ block mechanism suppresses NMDAR activity when the postsynaptic cell is inactive. Although the importance of NMDARs in associative learning and long-term memory (LTM) formation has been demonstrated, the role of Mg2+ block in these processes remains unclear. Using transgenic flies expressing NMDARs defective for Mg2+ block, we found that Mg2+ block mutants are defective for LTM formation but not associative learning. We demonstrate that LTM-dependent increases in expression of synaptic genes, including homer, staufen, and activin, are abolished in flies expressing Mg2+ block defective NMDARs. Furthermore, we show that genetic and pharmacological reduction of Mg2+ block significantly increases expression of a CREB repressor isoform. Our results suggest that Mg2+ block of NMDARs functions to suppress basal expression of a CREB repressor, thus permitting CREB-dependent gene expression upon LTM induction.