Differential Expression Patterns of Lynx Proteins and Involvement of Lynx1 in Prepulse Inhibition

Negative allosteric modulators, such as lynx1 and lynx2, directly interact with nicotinic acetylcholine receptors (nAChRs). The nAChRs are integral to cholinergic signaling in the brain and have been shown to mediate different aspects of cognitive function. Given the interaction between lynx proteins and these receptors, we examined whether these endogenous negative allosteric modulators are involved in cognitive behaviors associated with cholinergic function. We found both cell-specific and overlapping expression patterns of lynx1 and lynx2 mRNA in brain regions associated with cognition, learning, memory, and sensorimotor processing, including the prefrontal cortex (PFC), cingulate cortex, septum, hippocampus, amygdala, striatum, and pontine nuclei. Since lynx proteins are thought to play a role in conditioned associations and given the expression patterns across brain regions, we first assessed whether lynx knockout mice would differ in a cognitive flexibility task. We found no deficits in reversal learning in either the lynx1^–/– or lynx2^–/– knockout mice. Thereafter, sensorimotor gating was examined with the prepulse inhibition (PPI) assessment. Interestingly, we found that both male and female lynx1^–/– mice exhibited a deficit in the PPI behavioral response. Given the comparable expression of lynx2 in regions involved in sensorimotor gating, we then examined whether removal of the lynx2 protein would lead to similar behavioral effects. Unexpectedly, we found that while male lynx2^–/– mice exhibited a decrease in the baseline startle response, no differences were found in sensorimotor gating for either male or female lynx2^–/– mice. Taken together, these studies provide insight into the expression patterns of lynx1 and lynx2 across multiple brain regions and illustrate the modulatory effects of the lynx1 protein in sensorimotor gating.

Nicotine up-regulates alpha4beta2 nicotinic receptors and ER exit sites via stoichiometry-dependent chaperoning

The up-regulation of α4β2* nicotinic acetylcholine receptors (nAChRs) by chronic nicotine is a cell-delimited process and may be necessary and sufficient for the initial events of nicotine dependence. Clinical literature documents an inverse relationship between a person’s history of tobacco use and his or her susceptibility to Parkinson’s disease; this may also result from up-regulation. This study visualizes and quantifies the subcellular mechanisms involved in nicotine-induced nAChR up-regulation by using transfected fluorescent protein (FP)-tagged α4 nAChR subunits and an FP-tagged Sec24D endoplasmic reticulum (ER) exit site marker. Total internal reflection fluorescence microscopy shows that nicotine (0.1 µM for 48 h) up-regulates α4β2 nAChRs at the plasma membrane (PM), despite increasing the fraction of α4β2 nAChRs that remain in near-PM ER. Pixel-resolved normalized Förster resonance energy transfer microscopy between α4-FP subunits shows that nicotine stabilizes the (α4)₂(β2)₃ stoichiometry before the nAChRs reach the trans-Golgi apparatus. Nicotine also induces the formation of additional ER exit sites (ERES). To aid in the mechanistic analysis of these phenomena, we generated a β2_{enhanced-ER-export} mutant subunit that mimics two regions of the β4 subunit sequence: the presence of an ER export motif and the absence of an ER retention/retrieval motif. The α4β2_{enhanced-ER-export} nAChR resembles nicotine-exposed nAChRs with regard to stoichiometry, intracellular mobility, ERES enhancement, and PM localization. Nicotine produces only small additional PM up-regulation of α4β2_{enhanced-ER-export} receptors. The experimental data are simulated with a model incorporating two mechanisms: (1) nicotine acts as a stabilizing pharmacological chaperone for nascent α4β2 nAChRs in the ER, eventually increasing PM receptors despite a bottleneck(s) in ER export; and (2) removal of the bottleneck (e.g., by expression of the β2_{enhanced-ER-export} subunit) is sufficient to increase PM nAChR numbers, even without nicotine. The data also suggest that pharmacological chaperoning of nAChRs by nicotine can alter the physiology of ER processes.

Nicotine is a selective pharmacological chaperone of acetylcholine receptor number and stoichiometry. Implications for drug discovery

The acronym SePhaChARNS, for "selective pharmacological chaperoning of acetylcholine receptor number and stoichiometry," is introduced. We hypothesize that SePhaChARNS underlies classical observations that chronic exposure to nicotine causes "upregulation" of nicotinic receptors (nAChRs). If the hypothesis is proven, (1) SePhaChARNS is the molecular mechanism of the first step in neuroadaptation to chronic nicotine; and (2) nicotine addiction is partially a disease of excessive chaperoning. The chaperone is a pharmacological one, nicotine; and the chaperoned molecules are alpha4beta2* nAChRs. SePhaChARNS may also underlie two inadvertent therapeutic effects of tobacco use: (1) the inverse correlation between tobacco use and Parkinson's disease; and (2) the suppression of seizures by nicotine in autosomal dominant nocturnal frontal lobe epilepsy. SePhaChARNS arises from the thermodynamics of pharmacological chaperoning: ligand binding, especially at subunit interfaces, stabilizes AChRs during assembly and maturation, and this stabilization is most pronounced for the highest-affinity subunit compositions, stoichiometries, and functional states of receptors. Several chemical and pharmacokinetic characteristics render exogenous nicotine a more potent pharmacological chaperone than endogenous acetylcholine. SePhaChARNS is modified by desensitized states of nAChRs, by acid trapping of nicotine in organelles, and by other aspects of proteostasis. SePhaChARNS is selective at the cellular, and possibly subcellular, levels because of variations in the detailed nAChR subunit composition, as well as in expression of auxiliary proteins such as lynx. One important implication of the SePhaChARNS hypothesis is that therapeutically relevant nicotinic receptor drugs could be discovered by studying events in intracellular compartments rather than exclusively at the surface membrane.

Patients with constipation-predominant irritable bowel syndrome (IBS) may have elevated serotonin concentrations in colonic mucosa as compared with diarrhea-predominant patients and subjects with normal bowel habits

BACKGROUND

Serotonin (5-HT) may play an important role in the regulation of colonic motility in humans. However, it is not known whether alterations in the colonic 5-HT system are involved in the pathophysiology of irritable bowel syndrome (IBS).

METHODS

Colonic mucosal specimens ranging from the ascending colon to the rectum were obtained from patients with diarrhea- or constipation-predominant IBS (n = 7 and n = 8, respectively) and from subjects with normal bowel habits (n = 7) by endoscopic biopsy in order to determine whether patients with different clinical manifestations of IBS have different mucosal disposition of 5-HT. The tissue concentrations of 5-HT and its major metabolite, 5-hydroxyindoleacetic acid, were determined by reversed-phase high-performance liquid chromatography with fluorescence detection.

RESULTS

In all study groups, the mean mucosal 5-HT concentrations obtained from the rectum were significantly (p < 0.05) higher than those obtained from more cephalic regions of the colon. In addition, the overall mean mucosal 5-HT concentrations obtained from patients with constipation-predominant IBS were significantly (p < 0.05) higher than those obtained from the control subjects and patients with diarrhea-predominant IBS. No significant differences were observed in 5-hydroxyindoleacetic acid concentrations among the three groups.

CONCLUSIONS

The mucosal 5-HT concentrations in the colon showed an ascending cephalocaudal gradient in all study groups. Although the mucosal 5-HT concentrations were elevated in patients with constipation-predominant IBS as compared with those with diarrhea-predominant IBS and the control subjects, further studies are necessary to determine whether the elevated mucosal 5-HT is a cause or a result of abnormal colonic motility.

Long-term nicotine adaptation in Caenorhabditis elegans involves PKC-dependent changes in nicotinic receptor abundance

Chronic exposure to nicotine leads to long-term changes in both the abundance and activity of nicotinic acetylcholine receptors, processes thought to contribute to nicotine addiction. We have found that in Caenorhabditis elegans, prolonged nicotine treatment results in a long-lasting decrease in the abundance of nicotinic receptors that control egg-laying. In naive animals, acute exposure to cholinergic agonists led to the efficient stimulation of egg-laying, a response mediated by a nicotinic receptor functionally expressed in the vulval muscle cells. Overnight exposure to nicotine led to a specific and long-lasting change in egg-laying behavior, which rendered the nicotine-adapted animals insensitive to simulation of egg-laying by the nicotinic agonist and was accompanied by a promoter-independent reduction in receptor protein levels. Mutants defective in the gene tpa-1, which encodes a homolog of protein kinase C (PKC), failed to undergo adaptation to nicotine; after chronic nicotine exposure they remained sensitive to cholinergic agonists and retained high levels of receptor protein in the vulval muscles. These results suggest that PKC-dependent signaling pathways may promote nicotine adaptation via regulation of nicotinic receptor synthesis or degradation.

Atypical protein kinase C cooperates with PAR-3 to establish embryonic polarity in Caenorhabditis elegans

Asymmetric cell divisions, critically important to specify cell types in the development of multicellular organisms, require polarized distribution of cytoplasmic components and the proper alignment of the mitotic apparatus. In Caenorhabditis elegans, the maternally expressed protein, PAR-3, is localized to one pole of asymmetrically dividing blastomeres and is required for these asymmetric divisions. In this paper, we report that an atypical protein kinase C (PKC-3) is essential for proper asymmetric cell divisions and co-localizes with PAR-3. Embryos depleted of PKC-3 by RNA interference die showing Par-like phenotypes including defects in early asymmetric divisions and mislocalized germline-specific granules (P granules). The defective phenotypes of PKC-3-depleted embryos are similar to those exhibited by mutants for par-3 and another par gene, par-6. Direct interaction of PKC-3 with PAR-3 is shown by in vitro binding analysis. This result is reinforced by the observation that PKC-3 and PAR-3 co-localize in vivo. Furthermore, PKC-3 and PAR-3 show mutual dependence on each other and on three of the other par genes for their localization. We conclude that PKC-3 plays an indispensable role in establishing embryonic polarity through interaction with PAR-3.

Mutations in genes encoding extracellular matrix proteins suppress the emb-5 gastrulation defect in Caenorhabditis elegans

The second division of the gut precursor E cells is lethally accelerated during Caenorhabditis elegans gastrulation by mutations in the emb-5 gene, which encodes a presumed nuclear protein. We have isolated suppressor mutations of the temperature-sensitive allele emb-5(hc61), screened for them among dpy and other mutations routinely used as genetic markers, and identified eight emb-5 suppressor genes. Of these eight suppressor genes, at least four encode extracellular matrix proteins, i.e., three collagens and one proteoglycan. The suppression of the emb-5 gastrulation defect seemed to require the maternal expression of the suppressors. Phenotypically, the suppressors by themselves slowed down early embryonic cell divisions and corrected the abnormal cell-division sequence of emb-5 mutant embryos. We propose an indirect stress-response mechanism to be the main cause of the suppression because: (1) none of these suppressors is specific, either to particular temperature-sensitive emb-5 alleles or to the emb-5 gene; (2) suppressible alleles of genes, reported here or elsewhere, are temperature sensitive or weak; (3) the suppression is not strong but marginal; (4) the suppression itself shows some degree of temperature dependency; and (5) none of the extracellular matrix proteins identified here is known to be expressed in oocytes or early embryos, despite the present observation that the suppression is maternal.

Molecular evidence for the direct involvement of a protein kinase C in developmental and behavioural susceptibility to tumour-promoting phorbol esters in Caenorhabditis elegans

The nematode Caenorhabditis elegans displays developmental and behavioural sensitivity to tumour-promoting phorbol esters. This sensitivity involves the gene tpa-1, which encodes two protein kinase C isoforms, TPA-1A and TPA-1B. Here we report the molecular nature of the sensitivity in this animal. Characterization of transposon Tc1-induced phorbol ester-resistant mutants has revealed that Tc1 was inserted in a region encoding the kinase domain, resulting in the loss of tpa-1 products. Introduction of a genomic DNA containing the entire wild-type tpa-1 locus into a Tc1-inserted mutant restored the sensitivity to tumour promoters, and tpa-1 products were also produced. These results suggest that the function of wild-type TPA-1 is necessary and sufficient for tumour promoters to cause developmental and behavioural sensitivity in C. elegans.

The tpa-1 gene of Caenorhabditis elegans encodes two proteins similar to Ca(2+)-independent protein kinase Cs: evidence by complete genomic and complementary DNA sequences of the tpa-1 gene

The gene tpa-1 on chromosome IV of the nematode Caenorhabditis elegans plays a major and definitive role in the adversary action of tumour-promoting phorbol esters, which induce growth arrest and locomotory distress in the animal. The gene was deduced to code for a protein kinase C (PKC) homologue by molecular cloning. We have now sequenced the complete genomic and complementary DNAs for tpa-1 and have analysed their structural features in detail: (1) tpa-1 spans over 20 kb consisting of eleven exons and ten introns; (2) two different-sized mRNAs are generated from the tpa-1 locus; (3) both mRNAs are trans-spliced to the trans-spliced leader SL1; (4) both mRNAs encode PKC isoforms, which are most similar to Ca(2+)-independent novel PKC0; (5) the two PKC isoforms differ from each other in that the smaller lacks the amino-terminal region of the larger corresponding to the first four exons and a portion of the fifth exon; and (6) three introns are located at; identical positions in the polypeptide sequences aligned between the C. elegans tpa-1 product and a PKC of the fruit fly Drosophila melanogaster.

The C. elegans unc-18 gene encodes a protein expressed in motor neurons

The C. elegans unc-18 gene is required to maintain normal acetylcholine levels. We determined the complete structure of an unc-18 cDNA that encodes a protein of 591 highly charged and hydrophilic amino acids. The protein shows sequence similarity with elements of the secretory pathway in the yeast S. cerevisiae. Antibodies raised against a portion of the unc-18-encoded protein (UNC-18) detected a 68 kd soluble antigen on immunoblots and intensely stained all vertical cord motor neurons in situ. These findings suggest that UNC-18 participates in the axonal transport system and influences the acetylcholine flow in motor neurons.

A role of ADF chemosensory neurones in dauer formation behaviour in C. elegans

In Caenorhabditis elegans, mutants in osmotic avoidance behaviour (osm), which fail to avoid high concentrations of salts and sugars, have been previously identified. These osm mutants are also defective in dauer larva formation, and fail to take up fluorescein dye in six pairs of amphid neurones (ADF, ADL, ASH, ASI, ASJ, and ASK) and two pairs of phasmid neurones. Analysis of the FITC dye uptake by osm-3 mutants show that seven of the eight osm-3 alleles can take up FITC dyes in one pair of amphid neurones, ADF. Comparison of dauer larva formation behaviour in different osm-3 alleles shows a direct correlation between improved behaviour and FITC dye uptake. Therefore, these allelic strains are useful in defining the role of ADF neurones in dauer larva formation.

C. elegans osm-3 gene mediating osmotic avoidance behaviour encodes a kinesin-like protein

In the nematode Caenorhabditis elegans, mutants in osm-3 gene are known to be defective in osmotic avoidance, chemotaxis and dauer formation behaviours. To study the molecular basis of these pleiotropic defects we have cloned the osm-3 gene by germline transformation of osm-3 (p802) mutants through microinjection of the wild type genomic DNA. Northern analysis reveals a 3.0 kb transcript corresponding to osm-3. DNA sequencing of the transforming 4.3 kb fragment revealed a kinesin heavy chain-like protein, which contains conserved ATPase and microtubule binding domains. Our results are consistent with the previous EM data on osm-3 (p802) mutants that show an accumulation of dense matrix material in the amphid sheath cytoplasm and a shortened distal segment of the amphid channel cilium. These data suggest a kinesin-like role of the osm-3 product in axonal transport.

emb-5, a gene required for the correct timing of gut precursor cell division during gastrulation in Caenorhabditis elegans, encodes a protein similar to the yeast nuclear protein SPT6

The emb-5 gene is required for the correct timing of division of gut precursor cells during gastrulation in Caenorhabditis elegans. We have now characterized the molecular structure of emb-5. The predicted emb-5-encoded protein (EMB-5) possesses an extremely acidic amino-terminus and overall similarity to the Saccharomyces cerevisiae nuclear protein SPT6, which has been shown to affect the transcription of a variety of genes and suggested to play a role in chromatin assembly or modification. EMB-5 may function in the control of cell cycle timing by modulating chromatin structure and consequently affects morphogenesis of C. elegans.

The unc-18 Gene Encodes a Novel Protein Affecting the Kinetics of Acetylcholine Metabolism in the Nematode Caenorhabditis elegans

Genes affecting acetylcholine (ACh) levels without influencing choline acetyltransferase activity have been identified in Caenorhabditis elegans. We have examined one such gene, unc-18. We isolated a transposon-insertion allele for unc-18 and used it to clone a genomic region containing the unc-18 locus. The unc-18 location within this region was determined by rescuing the unc-18 mutant phenotype in a germ-line transformation experiment and identifying transcripts affected by four independent unc-18 mutations. A single-sized poly(A)+ RNA was synthesized from the gene. Expression of the transcript appears to be stage specific: The transcript is found in abundance at the early larval stage but in decreased amounts at the fourth larval and the adult stages. These results show that the unc-18 gene plays a role in development as well as in the kinetics of ACh metabolism.

Purification and characterization of protein kinase C from the nematode Caenorhabditis elegans

Protein kinase C (PKC) of Caenorhabditis elegans was identified by enzymatic activity and [3H]phorbol 12,13-dibutyrate binding after DEAE-Sephacel column chromatography of a crude cytosolic extract. Ca(2+)-dependent activation of nematode PKC was observed in the presence of phosphatidylserine. The enzyme was maximally activated by 1,2-dioleoylglycerol or phorbol 12-myristate 13-acetate in the presence of phosphatidylserine and Ca2+. Hydroxyapatite column chromatography showed only one peak of PKC activity with histone H1 and myelin basic protein as substrates. The enzyme was purified to near homogeneity by sequential chromatography on polylysine-agarose and phosphatidylserine affinity columns. The purified protein showed a molecular mass of 79 kDa on SDS/PAGE. The substrate specificity of the C. elegans enzyme was shown to be different from that of mammalian PKCs. Here we describe some of the properties of the nematode enzyme.

Mutations in a protein kinase C homolog confer phorbol ester resistance on Caenorhabditis elegans

The tpa-1 gene mediates the action of tumor-promoting phorbol esters in the nematode Caenorhabditis elegans. A genomic fragment that constitutes a portion of the tpa-1 gene was cloned by Tc1 transposon tagging and was used as a probe to screen a nematode complementary DNA library. One of the isolated complementary DNA clones had a nucleotide sequence that predicts a polypeptide of 526 amino acids. The predicted amino acid sequence revealed that the predicted tpa-1 protein sequence is highly similar to protein kinase C molecules from various animals, including man.

A gene involved in action of tumor promoters is identified and mapped in Caenorhabditis elegans

We isolated mutants of the nematode Caenorhabditis elegans resistant to 12-O-tetradecanoylphorbol-13-acetate (TPA). The TPA-resistant mutants, although they grew somewhat smaller than normal, reproduced well and behaved normally in TPA; they also did similarly in another phorbol ester tumor promoter, phorbol-12,13-didecanoate (PDD), thus proving they are also resistant to PDD. All the mutations defined by these TPA-resistant mutants were semidominant to the wild-type allele. The 15 independently isolated mutants all fell into the same complementation group, defining a single gene, tpa-1. The gene tpa-1 mapped near the marker gene dpy-9 on chromosome IV.

Tumor promoters specifically and reversibly disturb development and behavior of Caenorhabditis elegans

The effect of phorbol ester tumor promoters on the development and behavior of a free-living soil nematode, Caenorhabditis elegans, was studied. When young developing C. elegans were grown on E. coli-seeded agar with low concentrations (0.1 microgram/ml) of 12-0-tetradecanoyl-phorbol-13-acetate or phorbol-12,13-didecanoate, their growth was arrested. These tumor promoters reduced the brood size when gravid adults were treated and caused uncoordinated movement in animals treated at any stage of development. The effects of these tumor promoters on nematode development and behavior were partially reversible. The nonpromoting derivatives phorbol and 4 alpha-phorbol-12,13-didecanoate showed no effect on the animals.

Life span of the wild and mutant nematode Caenorhabditis elegans. Effects of sex, sterilization, and temperature

The survival of Caenorhabditis elegans was studied comparing animals of different sexes, sterilized animals, and animals grown at different temperatures as a prelude to more detailed cytological and genetic analysis of aged nematodes. Temperature-sensitive sterile mutants, animals sterilized by 5-fluorodeoxyuridine treatment, and wild-type males showed little difference in life span from that of wild-type hermaphrodites, although slight changes in P (time of beginning of the dying phase) or T1/2 (half-life of the population in the early dying phase) values were observed. At higher temperatures, P and T1/2 values markedly decreased, indicating a shortened life span. Temperature shift between 16 degrees C and 25 degrees C revealed that an increase in life span always involved low temperatures after the adult phase. High temperature treatment during the growing phase or after the adult phase caused an earlier start of the dying phase, but a downward temperature during the adult phase resulted in a great increase in the half-life of the population (T1/2). The results suggest that the life span of C. elegans is rigidly determined by somatic cells and markedly influenced by the effects of temperature on the cells during the post-mitotic state.

Characterization of temperature-sensitive, fertilization-defective mutants of the nematode caenorhabditis elegans

The isolation and characterization of three Caenorhabditis elegans temperature-sensitive mutants that are defective at fertilization are described. All three are alleles of the gene fer-1. At the restrictive temperature of 25 degrees, mutant hermaphrodites make sperm and oocytes in normal numbers. No oocytes are fertilized, although they pass through the spermatheca and uterus normally. The oocytes can be fertilized by sperm transferred by wild-type males, indicating that the mutant defect is in the sperm. The temperature-sensitive period for the mutants coincides with spermatogenesis. Sperm made by mutants at 25 degrees cannot be distinguished from wild-type sperm by light microscopy. The sperm do contact oocytes in mutant hermaphrodites, but do not fertilize. Mutant sperm appear to be nonmotile. Mutant males are also steril when grown at 25 degrees. They trnasfer normal numbers of sperm to hermaphrodites at mating, but these sperm fail to migrate to the spermatheca and are infertile. The phenotype of these mutants is consistent with a primary defect in sperm motility, but the cause of this defect is not known.