Neural coding for olfactory sensory stimuli has been mapped near completion in the Drosophila first-order center, but little is known in the higher brain centers. Here, we report that the antenna lobe (AL) spatial map is transformed further in the calyx of the mushroom body (MB), an essential olfactory associated learning center, by stereotypic connections with projection neurons (PNs). We found that Kenyon cell (KC) dendrites are segregated into 17 complementary domains according to their neuroblast clonal origins and birth orders. Aligning the PN axonal map with the KC dendritic map and ultrastructural observation suggest a positional ordering such that inputs from the different AL glomeruli have distinct representations in the MB calyx, and these representations might synapse on functionally distinct KCs. Our data suggest that olfactory coding at the AL is decoded in the MB and then transferred via distinct lobes to separate higher brain centers.

SUMMARY During the lifespans of most animals, reproductive maturity and mating activity are highly coordinated. In Drosophila melanogaster, for instance, male fertility increases with age and older males are known to have a copulation advantage over young ones. The molecular and neural basis of this age-related disparity in mating behavior is unknown. Here we show that the Or47b odorant receptor is required for the copulation advantage of older males. Notably, the sensitivity of Or47b neurons to a stimulatory pheromone, palmitoleic acid, is low in young males but high in older ones, which accounts for older males’ higher courtship intensity. Mechanistically, this age-related sensitization of Or47b neurons requires a reproductive hormone, juvenile hormone, as well as its binding protein Methoprene-tolerant in Or47b neurons. Together, our study identifies a direct neural substrate for juvenile hormone that permits coordination of courtship activity with reproductive maturity to maximize male reproductive fitness.

Memory is initially labile and gradually consolidated over time through new protein synthesis into a long-lasting stable form. Studies of odor-shock associative learning in Drosophila have established the mushroom body (MB) as a key brain structure involved in olfactory long-term memory (LTM) formation. Exactly how early neural activity encoded in thousands of MB neurons is consolidated into protein-synthesis-dependent LTM remains unclear. Here, several independent lines of evidence indicate that changes in two MB vertical lobe V3 (MB-V3) extrinsic neurons are required and contribute to an extended neural network involved in olfactory LTM: (i) inhibiting protein synthesis in MB-V3 neurons impairs LTM; (ii) MB-V3 neurons show enhanced neural activity after spaced but not massed training; (iii) MB-V3 dendrites, synapsing with hundreds of MB α/β neurons, exhibit dramatic structural plasticity after removal of olfactory inputs; (iv) neurotransmission from MB-V3 neurons is necessary for LTM retrieval; and (v) RNAi-mediated downregulation of oo18 RNA-binding protein (involved in local regulation of protein translation) in MB-V3 neurons impairs LTM. Our results suggest a model of long-term memory formation that includes a systems-level consolidation process, wherein an early, labile olfactory memory represented by neural activity in a sparse subset of MB neurons is converted into a stable LTM through protein synthesis in dendrites of MB-V3 neurons synapsed onto MB α lobes.L ong-term memory (LTM) and long-term synaptic plasticity require de novo protein synthesis, which is regulated at transcriptional and/or translational levels in a synapse-specific manner (1-3). Synapse-specific plasticity during LTM formation in some contexts may involve local regulation of protein translation by a family of RNA-binding proteins, the cytoplasmic polyadenylation element-binding proteins (CPEBs) (2). Neuronal CPEBs have two conformational states. The inactive state predominates at low levels of CPEB expression and represses translation from nascent mRNAs. The active state is achieved either via a self-perpetuating prion-like state when expression levels surpass a threshold or via Ca 2+ /calmoduline-dependent protein kinase II (CaMKII)-mediated phosphorylation, and translation is initiated by elongation of an mRNA's poly-A tail (4-6). In other species, CPEB1 has been shown to contribute to long-term facilitation or potentiation (5, 7). In Drosophila, oo18 RNA-binding protein 2 (ORB2) appears required for long-term memory formation after courtship conditioning (8, 9). Any role for ORB in fruit fly memory formation, however, remains unclear.Drosophila can learn to associate an odor (conditioned stimulus, CS) with foot-shock punishment (unconditioned stimulus, US). This odor-shock association initially is labile, lasting for only about a day after one training session. With repetitive, spaced training (ST) sessions (rest intervals between each session), a protein synthesis-dependent, LTM is formed. With repetitive, massed training (MT) ses...

Infection with Helicobacter pylori cagA-positive strains is associated with gastritis, ulcerations, and gastric cancer. CagA is translocated into infected epithelial cells by a type IV secretion system and can be tyrosine phosphorylated, inducing signal transduction and motogenic responses in epithelial cells. Cellular cholesterol, a vital component of the membrane, contributes to membrane dynamics and functions and is important in VacA intoxication and phagocyte evasion during H. pylori infection. In this investigation, we showed that cholesterol extraction by methyl-␤-cyclodextrin reduced the level of CagA translocation and phosphorylation. Confocal microscope visualization revealed that a significant portion of translocated CagA was colocalized with the raft marker GM1 and c-Src during infection. Moreover, GM1 was rapidly recruited into sites of bacterial attachment by live-cell imaging analysis. CagA and VacA were cofractionated with detergent-resistant membranes (DRMs), suggesting that the distribution of CagA and VacA is associated with rafts in infected cells. Upon cholesterol depletion, the distribution shifted to non-DRMs. Accordingly, the CagA-induced hummingbird phenotype and interleukin-8 induction were blocked by cholesterol depletion. Raft-disrupting agents did not influence bacterial adherence but did significantly reduce internalization activity in AGS cells. Together, these results suggest that delivery of CagA into epithelial cells by the bacterial type IV secretion system is mediated in a cholesterol-dependent manner.

Highlights d Group housing enhances courtship motivation in mature but not immature males d Group housing elevates the pheromone response of Or47b ORNs only in mature males d CaMKI/CBP pathway synergizes with juvenile hormone in sensitizing Or47b ORNs d Fru M levels fine-tune pheromone sensitivity according to both fly density and age