In Drosophila, the most widely used system for generating spatially restricted transgene expression is based on the yeast GAL4 protein and its target upstream activating sequence (UAS). To permit temporal as well as spatial control over UAS-transgene expression, we have explored the use of a conditional RU486-dependent GAL4 protein (GeneSwitch) in Drosophila. By using cloned promoter fragments of the embryonic lethal abnormal vision gene or the myosin heavy chain gene, we have expressed GeneSwitch specifically in neurons or muscles and show that its transcriptional activity within the target tissues depends on the presence of the activator RU486 (mifepristone). We used available UAS-reporter lines to demonstrate RU486-dependent tissuespecific transgene expression in larvae. Reporter protein expression could be detected 5 h after systemic application of RU486 by either feeding or ''larval bathing.'' Transgene expression levels were dose-dependent on RU486 concentration in larval food, with low background expression in the absence of RU486. By using genetically altered ion channels as reporters, we were able to change the physiological properties of larval bodywall muscles in an RU486-dependent fashion. We demonstrate here the applicability of GeneSwitch for conditional tissue-specific expression in Drosophila, and we provide tools to control pre-and postsynaptic expression of transgenes at the larval neuromuscular junction during postembryonic life.

Neuroserpin is a serine protease inhibitor of the serpin family that has been identified as an axonally secreted glycoprotein in neuronal cultures of chicken dorsal root ganglia. To obtain an indication for possible functions of neuroserpin, we analyzed its expression in the developing and the adult CNS of the mouse. In the adult CNS, neuroserpin was most strongly expressed in the neocortex, the hippocampal formation, the olfactory bulb, and the amygdala. In contrast, most thalamic nuclei, the caudate putamen, and the cerebellar granule cells were devoid of neuroserpin mRNA. During embryonic development, neuroserpin mRNA was not detectable in neuroepithelia, but it was expressed in the differentiating fields of most CNS regions concurrent with their appearance. In the cerebellum, the granule cells and a subgroup of Purkinje cells were neuroserpin-positive during postnatal development. As a further step toward the elucidation of neuroserpin function, we performed a study to identify potential target proteases. In vitro, neuroserpin formed SDS-stable complexes and inhibited the amidolytic activity of tissue plasminogen activator, urokinase, and plasmin. In contrast, no complex formation with or inhibition of thrombin was found. Expression pattern and inhibitory specificity implicate neuroserpin as a candidate regulator of plasminogen activators, which have been suggested to participate in the modulation or reorganization of synaptic connections in the adult. During development, neuroserpin may attenuate extracellular proteolysis related to processes such as neuronal migration, axogenesis, or the formation of mature synaptic connections.

We have identified and chromatographically purified an axonally secreted glycoprotein of CNS and PNS neurons. Several peptides derived from it were microsequenced. Based on these sequences, a fragment of the corresponding cDNA was amplified and used as a probe to isolate a full length cDNA from a chicken brain cDNA library. Because the deduced amino acid sequence qualified the protein as a novel member of the serpin family of serine protease inhibitors, we called it neuroserpin. Analysis of the primary structural features further characterized neuroserpin as a heparin‐independent, functional inhibitor of a trypsin‐like serine protease. In situ hybridization revealed a predominantly neuronal expression during the late stages of neurogenesis and in the adult brain in regions which exhibit synaptic plasticity. Thus, neuroserpin might function as an axonally secreted regulator of the local extracellular proteolysis involved in the reorganization of the synaptic connectivity during development and synapse plasticity in the adult.

We describe here a general technique for the graded inhibition of cellular excitability in vivo. Inhibition is accomplished by expressing a genetically modified Shaker K(+) channel (termed the EKO channel) in targeted cells. Unlike native K(+) channels, the EKO channel strongly shunts depolarizing current: activating at potentials near E(K) and not inactivating. Selective targeting of the channel to neurons, muscles, and photoreceptors in Drosophila using the Gal4-UAS system results in physiological and behavioral effects consistent with attenuated excitability in the targeted cells, often with loss of neuronal function at higher transgene dosages. By permitting the incremental reduction of electrical activity, the EKO technique can be used to address a wide range of questions regarding neuronal function.

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Neuroserpin is an axonally secreted serine proteinase inhibitor that is expressed in neurons during embryogenesis and in the adult nervous system. To identify target proteinases, we used a eucaryotic expression system based on the mouse myeloma cell line J558L and vectors including a promoter from an Ig--variable region, an Ig-enhancer, and the exon encoding the Igconstant region (C) and produced recombinant neuroserpin as a wild-type protein or as a fusion protein with C. We investigated the capability of recombinant neuroserpin to form SDS-stable complexes with, and to reduce the amidolytic activity of, a variety of serine proteinases in vitro. Consistent with its primary structure at the reactive site, neuroserpin exhibited inhibitory activity against trypsin-like proteinases. Although neuroserpin bound and inactivated plasminogen activators and plasmin, no interaction was observed with thrombin. A reactive site mutant of neuroserpin neither formed complexes with nor inhibited the amidolytic activity of any of the tested proteinases. Kinetic analysis of the inhibitory activity revealed neuroserpin to be a slow binding inhibitor of plasminogen activators and plasmin. Thus, we postulate that neuroserpin could represent a regulatory element of extracellular proteolytic events in the nervous system mediated by plasminogen activators or plasmin.Extracellular proteolysis exerted by serine proteinases has been implicated in a variety of processes in the nervous system during development and in adulthood. Among the serine proteinases recently reported to play a role in neural development and function, there are several well known proteins that had previously been found and characterized in nonneuronal functions, in particular blood coagulation and fibrinolysis. For example, tissue-type plasminogen activator (tPA) 1 and urokinase plasminogen activator (uPA) were found to be expressed in the nervous system (1, 2), and they have been demonstrated to be engaged in developmental processes such as cerebellar granule cell migration (3, 4), Schwann cell migration, and wrapping of axons (5), or neuromuscular synapse elimination (6). In the period of neurite outgrowth, plasminogen activators (PAs) have been found to be secreted at the growth cones of cultured neurons or neuronal cell lines (7,8), and they were demonstrated to modify the molecular composition of the neurites' substrata in vitro (9). In the adult nervous system, tPA is induced in the hippocampus after seizure, kindling, and long term potentiation (LTP) (10) and in the cerebellum after motor learning tasks (11), and mice lacking the gene for tPA (12) show a different form of hippocampal LTP (13,14). Furthermore, tPA has been demonstrated to be involved in excitotoxin-induced neuronal cell death in the murine hippocampus by converting locally secreted plasminogen to active plasmin (15, 16). Thrombin, which has been extensively characterized due to its important function in the blood clotting system, has been reported to be expressed in the nervous system (17). I...

Axonin-I is an axon-associated cell adhesion molecule (AxCAM) of the chicken, which promotes neurite outgrowth by interaction with the AxCAM Ll(G4) of the neuritic membrane. Here we report the cloning and sequence determination of a cDNA encoding axonin-I, Peptides generated by enzymatic cleavage showed similarity to the AxCAM F11. Degenerated polymerase chain reaction (PCR) primers were designed and an axonin-I fragment was amplified from mRNA of embryonic retina. Screening of a cDNA library from embryonic brain resulted in the isolation of a 4.0-kb cDNA insert with an open reading frame of 3108 nucleotides. The deduced polypeptide of 1036 amino acids includes a putative hydrophobic N-terminal signal sequence of 23 or 25 amino acids and a C-terminal hydrophobic sequence of 29 amino acids which is suggestive of sequences serving as signal for the attachment of a glycosyl-phosphatidylinositol (glycosyl-PtdIns) anchor. The putative mature form of axonin-1 comprises six immunoglobulin-like repeats, followed by four fibronectin-type I11 repeats.Axonin-1 exhibits 75% amino acid identity with the AxCAM TAG-1 of the rat, suggesting that it is the chicken homologue of TAG-1. Like TAG-1, axonin-I is glycosyl-PtdIns-anchored to the neuronal membrane; in contrast to TAG-1, it does not exhibit an Arg-Gly-Asp sequence.The interconnection of neurons by processes forming synaptic contacts is one of the crucial developmental stages of neurogenesis. In order to span long distances, bundles of axons are formed in a process which is thought to be driven by the tendency of growing axons to adhere specifically to and elongate along preexisting axons. The consistency with which

There is a critical need for genetic methods for the inducible expression of transgenes in specific cells during development. A promising approach for this is the GeneSwitch GAL4 system of Drosophila. With GeneSwitch GAL4 the expression of upstream activating sequence (UAS) effector lines is controlled by a chimeric GAL4 protein that becomes active in the presence of the steroid RU486 (mifepristone). To improve the utility of this expression system, we performed a large-scale enhancer-trap screen for insertions that yielded nervous system expression. A total of 204 GeneSwitch GAL4 lines with various larval expression patterns in neurons, glia, and/or muscle fibers were identified for chromosomes I-III. All of the retained lines show increased activity when induced with RU486. Many of the lines reveal novel patterns of sensory neurons, interneurons, and glia. There were some tissue-specific differences in background expression, with muscles and glia being more likely to show activity in the absence of the inducing agent. However, .90% of the neuron-specific driver lines showed little or no background activity, making them particularly useful for inducible expression studies.