We identified the Drosophila trio gene, which encodes a Dbl family protein carrying two Dbl homology (DH) domains, each of which potentially activates Rho family GTPases. Trio was distributed along axons in the central nervous system (CNS) of embryos and was strongly expressed in subsets of brain regions, including the mushroom body (MB). Loss-of-function trio mutations resulted in the misdirection or stall of axons in embryos and also caused malformation of the MB. The MB phenotypes were attributed to alteration in the intrinsic nature of neurites, as revealed by clonal analyses. Thus, Trio is essential in order for neurites to faithfully extend on the correct pathways. In addition, the localization of Trio in the adult brain suggests its postdevelopmental role in neurite terminals.

Microglia perform both neuroprotective and neurotoxic functions in the brain, with this depending on their state of activation and their release of mediators. Upon P2X(7) receptor stimulation, for example, microglia release small amounts of TNF, which protect neurons, whereas LPS causes massive TNF release leading to neuroinflammation. Here we report that, in rat primary cultured microglia, nicotine enhances P2X(7) receptor-mediated TNF release, whilst suppressing LPS-induced TNF release but without affecting TNF mRNA expression via activation of alpha7 nicotinic acetylcholine receptors (alpha7 nAChRs). In microglia, nicotine elicited a transient increase in intracellular Ca(2+) levels, which was abolished by specific blockers of alpha7 nAChRs. However, this response was independent of extracellular Ca(2+) and blocked by U73122, an inhibitor of phospholipase C (PLC), and xestospongin C, a blocker of the IP(3) receptor. Repeated experiments showed that currents were not detected in nicotine-stimulated microglia. Moreover, nicotine modulation of LPS-induced TNF release was also blocked by xestospongin C. Upon LPS stimulation, inhibition of TNF release by nicotine was associated with the suppression of JNK and p38 MAP kinase activation, which regulate the post-transcriptional steps of TNF synthesis. In contrast, nicotine did not alter any MAP kinase activation, but enhanced Ca(2+) response in P2X(7) receptor-activated microglia. In conclusion, microglial alpha7 nAChRs might drive a signaling process involving the activation of PLC and Ca(2+) release from intracellular Ca(2+) stores, rather than function as conventional ion channels. This novel alpha7 nAChR signal may be involved in the nicotine modification of microglia activation towards a neuroprotective role by suppressing the inflammatory state and strengthening the protective function.

An essential feature of the organization and function of the vertebrate and insect olfactory systems is the generation of a variety of olfactory receptor neurons (ORNs) that have different specificities in regard to both odorant receptor expression and axonal targeting. Yet the underlying mechanisms that generate this neuronal diversity remain elusive. Here we demonstrate that the Notch signal is involved in the diversification of ORNs in Drosophila melanogaster. A systematic clonal analysis showed that a cluster of ORNs housed in each sensillum were differentiated into two classes, depending on the level of Notch activity in their sibling precursors. Notably, ORNs of different classes segregated their axonal projections into distinct domains in the antennal lobes. In addition, both the odorant receptor expression and the axonal targeting of ORNs were specified according to their Notch-mediated identities. Thus, Notch signaling contributes to the diversification of ORNs, thereby regulating multiple developmental events that establish the olfactory map in Drosophila.

The Drosophila fruitless (fru) gene encodes a set of putative transcription factors that promote male sexual behavior by controlling the development of sexually dimorphic neuronal circuitry. However, the mechanism whereby fru establishes the sexual fate of neurons remains enigmatic. Here, we show that Fru forms a complex with the transcriptional cofactor Bonus (Bon), which, in turn, recruits either of two chromatin regulators, Histone deacetylase 1 (HDAC1), which masculinizes individual sexually dimorphic neurons, or Heterochromatin protein 1a (HP1a), which demasculinizes them. Manipulations of HDAC1 or HP1a expression change the proportion of male-typical neurons and female-typical neurons rather than producing neurons with intersexual characteristics, indicating that on a single neuron level, this sexual switch operates in an all-or-none manner.