Pattern formation in Drosophila depends initially on the translational activation of maternal messenger RNAs (mRNAs) whose protein products determine cell fate. Three mRNAs that dictate anterior, dorsoventral, and terminal specification--bicoid, Toll, and torso, respectively--showed increases in polyadenylate [poly(A)] tail length concomitant with translation. In contrast, posteriorly localized nanos mRNA, although also translationally activated, was not regulated by poly(A) status. These results implicate at least two mechanisms of mRNA activation in flies. Studies with bicoid mRNA showed that cytoplasmic polyadenylation is necessary for translation, establishing this pathway as essential for embryogenesis. Combined, these experiments identify a regulatory pathway that can coordinate initiation of maternal pattern formation systems in Drosophila.

Helicobacter pylori moves in response to environmental chemical cues using a chemotaxis twocomponent signal-transduction system. Autoinducer-2 (AI-2) is a quorum-sensing signal produced by the LuxS protein that accumulates in the bacterial environment in a densitydependent manner. We showed previously that a H. pylori luxS mutant was defective in motility on soft agar plates. Here we report that deletion of the luxS gene resulted in swimming behaviour with a reduced frequency of stops as compared to the wild-type strain. Stopping frequency was restored to wild-type levels by genetic complementation of the luxS mutation or by addition of synthetic 4,5-dihydroxy-2,3-pentanedione (DPD), which cyclizes to form AI-2. Synthetic DPD also increased the frequency of stops in wild-type H. pylori, similar to the behaviour induced by the known chemorepellent HCl. We found that whereas mutants lacking the chemoreceptor genes tlpA, tlpC or tlpD responded to an exogenous source of synthetic DPD, the chemoreceptor mutant tlpB was non-responsive to a gradient or uniform distribution of the chemical. Furthermore, a double mutant lacking both tlpB and luxS exhibited chemotactic behaviour similar to the tlpB single mutant, whereas a double mutant lacking both tlpB and the chemotransduction gene cheA behaved like a nonchemotactic cheA single mutant, supporting the model that tlpB functions in a signalling pathway downstream of luxS and upstream of cheA. We conclude that H. pylori perceives LuxS-produced AI-2 as a chemorepellent via the chemoreceptor TlpB.

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The gastric pathogen Helicobacter pylori forms biofilms on abiotic and biotic surfaces. We have shown previously that H. pylori perceives the quorum signal autoinducer-2 (AI-2) as a chemorepellent. We report here that H. pylori chemorepulsion from endogenous AI-2 influences the proportions and spatial organization of cells within biofilms. Strains that fail to produce AI-2 (∆luxS strains) or are defective for chemotaxis (∆cheA strains) formed more spatially homogenous biofilms with a greater proportion of adherent versus planktonic cells than wild-type biofilms. Reciprocally, a strain that overproduced AI-2 (luxSOP) formed biofilms with proportionally fewer adherent cells. Along with the known AI-2 chemoreceptor, TlpB, we identified AibA and AibB, two novel periplasmic binding proteins that are required for the AI-2 chemorepulsion response. Disruptions in any of the proteins required for AI-2 chemotaxis recapitulated the biofilm adherence and spatial organization phenotype of the ∆luxS mutant. Furthermore, exogenous administration of AI-2 was sufficient to decrease the proportion of adherent cells in biofilms and promote dispersal of cells from biofilms in a chemotaxis-dependent manner. Finally, we found that disruption of AI-2 production or AI-2 chemotaxis resulted in increased clustering of cells in microcolonies on cultured epithelial cells. We conclude that chemotaxis from AI-2 is a determinant of H. pylori biofilm spatial organization and dispersal.

Neuronal stem cell lineages are the fundamental developmental units of the brain, and neuronal circuits are the fundamental functional units of the brain. Determining lineage-circuitry relationships is essential for deciphering the developmental logic of circuit assembly. While the spatial distribution of lineage-related neurons has been investigated in a few brain regions [1-9], an important, but unaddressed question is whether temporal information that diversifies neuronal progeny within a single lineage also impacts circuit assembly. Circuits in the sensorimotor system (e.g., spinal cord) are thought to be assembled sequentially [10-14], making this an ideal brain region for investigating the circuit-level impact of temporal patterning within a lineage. Here, we use intersectional genetics, optogenetics, high-throughput behavioral analysis, single-neuron labeling, connectomics, and calcium imaging to determine how a set of bona fide lineage-related interneurons contribute to sensorimotor circuitry in the Drosophila larva. We show that Even-skipped lateral interneurons (ELs) are sensory processing interneurons. Late-born ELs contribute to a proprioceptive body posture circuit, whereas early-born ELs contribute to a mechanosensitive escape circuit. These data support a model in which a single neuronal stem cell can produce a large number of interneurons with similar functional capacity that are distributed into different circuits based on birth timing. In summary, these data establish a link between temporal specification of neuronal identity and circuit assembly at the single-cell level.