Abstract. Programmed cell death is an ongoing process in both the developing and the mature nervous system. The tumor suppressor gene, p53, can induce apoptosis in a number of different cell types. Recently, the enhanced expression of p53 has been observed during acute neurological disease. To determine whether p53 overexpression could influence neuronal survival, we used a recombinant adenovirus vector carrying wild type p53 to transduce postmitotic neurons. A control consisting of the same adenovirus vector background but carrying the lacZ reporter expression cassette was used to establish working parameters for the effective genetic manipulation of sympathetic neurons. We have found that recombinant adenovirus can be used at titers sufficiently high (10 to 50 multiplicity of infection) to transduce the majority of the neuronal population without perturbing survival, electrophysiological function, or cytoarchitecture. Moreover, we demonstrate that overexpression of wild type p53 is sufficient to induce programmed cell death in neurons. The observation that p53 is capable of inducing apoptosis in postmitotic neurons has major implications for the mechanisms of cell death in the traumatized mature nervous system.

The biliary glycoprotein (BGP)-encoding gene is a member of the human carcinoembryonic antigen (CEA) gene family. We have now cloned several mouse Bgp cDNAs from an outbred CDR-1 mouse colon cDNA library, as well as by reverse transcription-PCR amplification of colon RNA. The distinguishing features of the deduced Bgp protein isoforms are found in the two divergent N-terminal domains, the highly conserved internal C2-set immunoglobulin domains, and an intracytoplasmic domain of either 10 or 73 amino acids (aa). The cDNA structures suggest that these mRNAs are produced through alternative splicing of a Bgp gene and the usage of multiple transcriptional terminators. The Bgp deduced aa sequences are highly homologous to several well characterized rat hepatocyte proteins such as the cell CAM105/ecto-ATPase/pp120/HA4 proteins. Oligodeoxyribonucleotide probes representing the various cDNA isoform domains revealed predominant transcripts of 1.8, 3.1 and 4.0 kb on Northern analyses of mouse colon RNA; some of these bands are actually composed of several co-migrating transcripts. The transcripts encoding the long intracytoplasmic-tailed Bgp proteins are expressed at one-tenth the relative abundance of the shorter-tailed species. We have previously demonstrated that several mouse Bgp cDNAs, when transfected into eukaryotic cells, express BGP proteins at the cell surface and function in vitro as cell adhesion molecules, much like their human and rat counterparts. The expression of the many Bgp isoforms at the surface of epithelial cells, such as colon, suggests that these proteins play a determinant role, through self- or heterologous contact, in renewal and/or differentiation of their epithelia.

Normal cognitive and autonomic functions require nicotinic synaptic signaling. Despite the physiological importance of these synapses, little is known about molecular mechanisms that direct their assembly during development. We show here that the tumor-suppressor protein adenomatous polyposis coli (APC) functions in localizing ␣3-nicotinic acetylcholine receptors (nAChRs) to neuronal postsynaptic sites. Our quantitative confocal microscopy studies indicate that APC is selectively enriched at cholinergic synapses; APC surface clusters are juxtaposed to synaptic vesicle clusters and colocalize with ␣3-nAChRs but not with the neighboring synaptic glycine receptors or perisynaptic ␣7-nAChRs on chick ciliary ganglion (CG) neurons. We identify PSD (postsynaptic density)-93, ␤-catenin, and microtubule end binding protein EB1 as APC binding partners. PSD-93 and ␤-catenin are also enriched at ␣3-nAChR postsynaptic sites. EB1 shows close proximity to and partial overlap with ␣3-nAChR and APC surface clusters. We tested the role of APC in neuronal nicotinic synapse assembly by using retroviral-mediated in vivo overexpression of an APC dominant-negative (APC-dn) peptide to block the interaction of endogenous APC with both EB1 and PSD-93 during synapse formation in CG neurons. The overexpressed APC-dn led to dramatic decreases in ␣3-nAChR surface levels and clusters. Effects were specific to ␣3-nAChR postsynaptic sites; synaptic glycine receptor and perisynaptic ␣7-nAChR clusters were not altered. In addition, APC-dn also reduced surface membrane-associated clusters of PSD-93 and EB1. The results show that APC plays a key role in organizing excitatory cholinergic postsynaptic specializations in CG neurons. We identify APC as the first nonreceptor protein to function in localizing nAChRs to neuronal synapses in vivo.

The neuronal nicotinic synapse plays a central role in normal cognitive and autonomic function. Molecular mechanisms that direct the assembly of this synapse remain poorly defined, however. We show here that adenomatous polyposis coli (APC) organizes a multi-molecular complex that is essential for targeting α3*nAChRs to synapses. APC interaction with microtubule plus-end binding protein EB1 is required for α3*nAChR surface membrane insertion and stabilization. APC brings together EB1, the key cytoskeletal regulators macrophin and IQGAP1, and 14-3-3 adapter protein at nicotinic synapses. 14-3-3, in turn, links the α3-subunit to APC. This multi-molecular APC complex stabilizes the local microtubule and F-actin cytoskeleton and links postsynaptic components to the cytoskeleton-essential functions for controlling the molecular composition and stability of synapses. This work identifies macrophin, IQGAP1 and 14-3-3 as novel nicotinic synapse components and defines a new role for APC as an in vivo coordinator of nicotinic postsynaptic assembly in vertebrate neurons.

The exocytosis site of newly synthesized glycine receptor was defined by means of a morphological assay to characterize its export from the trans-Golgi Network to the plasma membrane. This was achieved by expressing in transfected neurons an alpha1 subunit bearing an N-terminal tag selectively cleavable from outside the cell by thrombin. This was combined with a transient temperature-induced block of exocytic transport that creates a synchronized exocytic wave. Immunofluorescence microscopy analysis of the cell surface appearance of newly synthesized receptor revealed that exocytosis mainly occurred at nonsynaptic sites in the cell body and the initial portion of dendrites. At the time of cell surface insertion, the receptors existed as discrete clusters. Quantitative analysis showed that glycine receptor clusters are stable in size and subsequently appeared in more distal dendritic regions. This localization resulted from diffusion in the plasma membrane and not from exocytosis of transport vesicles directed to dendrites. Kinetic analysis established a direct substrate-product relationship between pools of somatic and dendritic receptors. This indicated that clusters represent intermediates between newly synthesized and synaptic receptors. These results support a diffusion-retention model for the formation of receptor-enriched postsynaptic domains and not that of a vectorial intracellular targeting to synapses.

Synaptic efficacy requires that presynaptic and postsynaptic specializations align precisely and mature coordinately. The underlying mechanisms are poorly understood, however. We propose that adenomatous polyposis coli protein (APC) is a key coordinator of presynaptic and postsynaptic maturation. APC organizes a multiprotein complex that directs nicotinic acetylcholine receptor (nAChR) localization at postsynaptic sites in avian ciliary ganglion neurons in vivo. We hypothesize that the APC complex also provides retrograde signals that direct presynaptic active zones to develop in register with postsynaptic nAChR clusters. In our model, the APC complex provides retrograde signals via postsynaptic neuroligin that interacts extracellularly with presynaptic neurexin. S-SCAM (synaptic cell adhesion molecule) and PSD-93 (postsynaptic density-93) are scaffold proteins that bind to neuroligin. We identify S-SCAM as a novel component of neuronal nicotinic synapses. We show that S-SCAM, PSD-93, neuroligin and neurexin are enriched at ␣3*-nAChR synapses. PSD-93 and S-SCAM bind to APC and its binding partner ␤-catenin, respectively. Blockade of selected APC and ␤-catenin interactions, in vivo, leads to decreased postsynaptic accumulation of S-SCAM, but not PSD-93. Importantly, neuroligin synaptic clusters are also decreased. On the presynaptic side, there are decreases in neurexin and active zone proteins. Further, presynaptic terminals are less mature structurally and functionally. We define a novel neural role for APC by showing that the postsynaptic APC multiprotein complex is required for anchoring neuroligin and neurexin at neuronal synapses in vivo. APC human gene mutations correlate with autism spectrum disorders, providing strong support for the importance of the association, demonstrated here, between APC, neuroligin and neurexin.

Serotonin 5-HT 3 receptors (5-HT 3 Rs) are ligand-gated ion channels expressed by many peripheral neurons and are involved in several physiological processes. To learn more about the developmental regulation of 5-HT 3 R expression, we investigated rat sympathetic and vagal sensory neurons. We found that sympathetic and sensory neurons differ in their regulation of 5-HT 3 R expression during early postnatal life and as these neurons develop in culture. In SCG neurons 5-HT 3 R transcript levels are low at postnatal day 1 (P1) and increase 7.5-fold by P21; this increase occurs even after elimination of preganglionic innervation. In comparison, 5-HT 3 R mRNA levels in P1 nodose neurons are over 14-fold greater than in P1 SCG and change little by P21. We show that 5-HT 3 R transcript levels in nodose neurons depend on intact target innervation and drop by 60% after axotomy. When P1 SCG neurons develop in culture, we observed a significant increase in 5-HT 3 R expression: after 7 d in culture, transcript levels increase ninefold versus a threefold increase for neurons developing for 7 d in vivo. In contrast, 5-HT 3 R mRNA levels in cultured nodose neurons drop by 70% within 24 hr; however, this drop is transient. After 2 d, transcript levels begin to increase, and after 7 d, they are above initial values. We show that this delayed increase in 5-HT 3 R expression depends on neurotrophins. In both nodose and sympathetic neurons we found that the changes in 5-HT 3 R gene expression correlate directly with the appearance of 5-HTevoked current densities. Key words: 5-HT 3 receptor; ligand-gated ion channel; sympathetic; superior cervical ganglion; sensory; nodose; trigeminal; mRNA expression; neurotrophins; axotomyThe serotonin 5-HT 3 receptor (5-HT 3 R), a neurotransmittergated ion channel (Yakel and Jackson, 1988;Derkach et al., 1989;Maricq et al., 1991) present on many mammalian peripheral neurons, participates in several diverse physiological functions (Fozard, 1984;Jackson and Yakel, 1995). Activation of 5-HT 3 Rs located on peripheral vagal sensory nerve endings initiates reflexes affecting respiration, circulation, emesis, and swallowing (Douglas, 1975;Sanders-Bush and Mayer, 1996). 5-HT 3 Rs on spinal and vagal sensory neurons are involved in nociceptive signaling and nausea (Fozard, 1984). In the C NS 5-HT 3 Rs are implicated in anxiety, depression, and drug dependence (Apud, 1993;Greenshaw, 1993). In addition, 5-HT 3 Rs are expressed by sympathetic neurons; however, the role for these receptors in sympathetic f unction has not been f ully determined (Wallis and North, 1978;Yang et al., 1992).Many vagal afferent neurons expressing 5-HT 3 Rs are located in the nodose ganglion. These sensory neurons have typical unipolar polarities; their axons bif urcate into a peripheral branch that innervates much of the viscera, including heart, lungs, trachea, and gut, and a central branch that terminates mainly in the nucleus tractus solitarius (Andresen and Kunze, 1994). The physiological responses to serotonin elicited from ...

Individual cholinoceptive neurons express high levels of different neuronal nicotinic acetylcholine receptor (nAChR) subtypes, and target them to the appropriate synaptic regions for proper function. This review focuses on the intercellular and intracellular processes that regulate nAChR expression in vertebrate peripheral nervous system (PNS) and central nervous system (CNS) neurons. Specifically, we discuss the cellular and molecular mechanisms that govern the induction and maintenance of nAChR expression-innervation, target tissue interactions, soluble factors, and activity. We define the regulatory principles of interneuronal nicotinic synapse differentiation that have emerged from these studies. We also discuss the molecular players that target nAChRs to the surface membrane and the interneuronal synapse.