Complementation testing identifies genes mediating effects at quantitative trait loci underlying fear-related behavior

Knowing the genes involved in quantitative traits provides an entry point to understanding the biological bases of behavior, but there are very few examples where the pathway from genetic locus to behavioral change is known. To explore the role of specific genes in fear behavior, we mapped three fear-related traits, tested fourteen genes at six quantitative trait loci (QTLs) by quantitative complementation, and identified six genes. Four genes, Lamp, Ptprd, Nptx2, and Sh3gl, have known roles in synapse function; the fifth, Psip1, was not previously implicated in behavior; and the sixth is a long non-coding RNA, 4933413L06Rik, of unknown function. Variation in transcriptome and epigenetic modalities occurred preferentially in excitatory neurons, suggesting that genetic variation is more permissible in excitatory than inhibitory neuronal circuits. Our results relieve a bottleneck in using genetic mapping of QTLs to uncover biology underlying behavior and prompt a reconsideration of expected relationships between genetic and functional variation.

Complementation testing identifies causal genes at quantitative trait loci underlying fear related behavior

Knowing the genes involved in quantitative traits provides a critical entry point to understanding the biological bases of behavior, but there are very few examples where the pathway from genetic locus to behavioral change is known. Here we address a key step towards that goal by deploying a test that directly queries whether a gene mediates the effect of a quantitative trait locus (QTL). To explore the role of specific genes in fear behavior, we mapped three fear-related traits, tested fourteen genes at six QTLs, and identified six genes. Four genes, Lsamp, Ptprd, Nptx2 and Sh3gl, have known roles in synapse function; the fifth gene, Psip1, is a transcriptional co-activator not previously implicated in behavior; the sixth is a long non-coding RNA 4933413L06Rik with no known function. Single nucleus transcriptomic and epigenetic analyses implicated excitatory neurons as likely mediating the genetic effects. Surprisingly, variation in transcriptome and epigenetic modalities between inbred strains occurred preferentially in excitatory neurons, suggesting that genetic variation is more permissible in excitatory than inhibitory neuronal circuits. Our results open a bottleneck in using genetic mapping of QTLs to find novel biology underlying behavior and prompt a reconsideration of expected relationships between genetic and functional variation.

Single-cell methylation analysis of brain tissue prioritizes mutations that alter transcription

Relating genetic variants to behavior remains a fundamental challenge. To assess the utility of DNA methylation marks in discovering causative variants, we examined their relationship to genetic variation by generating single-nucleus methylomes from the hippocampus of eight inbred mouse strains. At CpG sequence densities under 40 CpG/Kb, cells compensate for loss of methylated sites by methylating additional sites to maintain methylation levels. At higher CpG sequence densities, the exact location of a methylated site becomes more important, suggesting that variants affecting methylation will have a greater effect when occurring in higher CpG densities than in lower. We found this to be true for a variant's effect on transcript abundance, indicating that candidate variants can be prioritized based on CpG sequence density. Our findings imply that DNA methylation influences the likelihood that mutations occur at specific sites in the genome, supporting the view that the distribution of mutations is not random.

Activity-Dependent Regulation of Alternative Cleavage and Polyadenylation During Hippocampal Long-Term Potentiation

Long-lasting forms of synaptic plasticity that underlie learning and memory require new transcription and translation for their persistence. The remarkable polarity and compartmentalization of neurons raises questions about the spatial and temporal regulation of gene expression within neurons. Alternative cleavage and polyadenylation (APA) generates mRNA isoforms with different 3′ untranslated regions (3′UTRs) and/or coding sequences. Changes in the 3′UTR composition of mRNAs can alter gene expression by regulating transcript localization, stability and/or translation, while changes in the coding sequences lead to mRNAs encoding distinct proteins. Using specialized 3′ end deep sequencing methods, we undertook a comprehensive analysis of APA following induction of long-term potentiation (LTP) of mouse hippocampal CA3-CA1 synapses. We identified extensive LTP-induced APA changes, including a general trend of 3′UTR shortening and activation of intronic APA isoforms. Comparison with transcriptome profiling indicated that most APA regulatory events were uncoupled from changes in transcript abundance. We further show that specific APA regulatory events can impact expression of two molecules with known functions during LTP, including 3′UTR APA of Notch1 and intronic APA of Creb1. Together, our results reveal that activity-dependent APA provides an important layer of gene regulation during learning and memory.

Mapping Gene Expression in Excitatory Neurons during Hippocampal Late-Phase Long-Term Potentiation

The persistence of long-lasting changes in synaptic connectivity that underlie long-term memory require new RNA and protein synthesis. To elucidate the temporal pattern of gene expression that gives rise to long-lasting neuronal plasticity, we analyzed differentially-expressed (DE) RNAs in mouse hippocampal slices following induction of late phase long-term potentiation (L-LTP) specifically within pyramidal excitatory neurons using Translating Ribosome Affinity Purification RNA sequencing (TRAP-seq). We detected time-dependent changes in up- and down-regulated ribosome-associated mRNAs over 2 h following L-LTP induction, with minimal overlap of DE transcripts between time points. TRAP-seq revealed greater numbers of DE transcripts and magnitudes of LTP-induced changes than RNA-seq of all cell types in the hippocampus. Neuron-enriched transcripts had greater changes at the ribosome-loading level than the total RNA level, while RNA-seq identified many non-neuronal DE mRNAs. Our results highlight the importance of considering both time course and cell-type specificity in activity-dependent gene expression during memory formation.

Anti-hyperalgesic effects of anti-serotonergic compounds on serotonin- and capsaicin-evoked thermal hyperalgesia in the rat

The peripheral serotonergic system has been implicated in the modulation of an array of pain states, from migraine to fibromyalgia; however, the mechanism by which serotonin (5HT) induces pain is unclear. Peripherally released 5HT induces thermal hyperalgesia, possibly via modulation of the transient receptor potential V1 (TRPV1) channel, which is gated by various noxious stimuli, including capsaicin. We previously reported in vitro that 5HT increases calcium accumulation in the capsaicin-sensitive population of sensory neurons with a corresponding increase in proinflammatory neuropeptide release, and both are antagonized by pretreatment with 5HT(2A) and 5HT(3) antagonists, as well as the anti-migraine drug sumatriptan. In the current study, we extended these findings in vivo using the rat hind paw thermal assay to test the hypothesis that peripheral 5HT enhances TRPV1-evoked thermal hyperalgesia that can be attenuated with 5HT(2A) and 5HT(3) receptor antagonists, as well as sumatriptan. Thermal hyperalgesia and edema were established by 5HT injection (0.1-10 nmol/100 μl) into the rat hind paw, and the latency to paw withdrawal (PWL) from noxious heat was determined. Rats were then pretreated with either 5HT before capsaicin (3 nmol/10 μl), the 5HT(2A) receptor antagonist ketanserin or the 5HT(3) receptor antagonist granisetron (0.0001-0.1 nmol/100 μl) before 5HT and/or capsaicin, or the 5HT(1B/1D) receptor agonist sumatriptan (0.01-1 nmol/100 μl) before capsaicin, and PWL was determined. We report that 5HT pretreatment enhances TRPV1-evoked thermal hyperalgesia, which is attenuated with local pretreatment with ketanserin, granisetron, or sumatriptan. We also report that peripheral 5HT induced a similar magnitude of thermal hyperalgesia in male and female rats. Overall, our results provide in vivo evidence supporting an enhancing role of 5HT on TRPV1-evoked thermal hyperalgesia, which can be attenuated by peripheral serotonergic intervention.

Changing Pax6 expression correlates with axon outgrowth and restoration of topography during optic nerve regeneration

Pax6, a member of the highly conserved developmental Pax gene family, plays a crucial role in early eye development and continues to be expressed in adult retinal ganglion cells (RGCs). Here we have used Western blots and immunohistochemistry to investigate the expression of Pax6 in the formation and refinement of topographic projections during optic nerve regeneration in zebrafish and lizard. In zebrafish with natural (12-h light/dark cycle) illumination, Pax6 expression in RGCs was decreased during axon outgrowth and increased during the restoration of the retinotectal map. Rearing fish in stroboscopic illumination to prevent retinotopic refinement resulted in a prolonged decrease in Pax6 levels; return to natural light conditions resulted in map refinement and restoration of normal Pax6 levels. In lizard, RGC axons spontaneously regenerate but remain in a persistent state of regrowth and do not restore topography; visual training during regeneration, however, allows a stabilization of connections and return of topography. Pax6 was persistently decreased in untrained animals but remained increased in trained ones. In both species, changes in expression were not due to cell division or cell death. The results suggest that decreased Pax6 expression is permissive for axon regeneration and extensive searching, while higher levels of Pax6 are associated with restoration of topography.

cAMP regulates axon outgrowth and guidance during optic nerve regeneration in goldfish

Increased cAMP improves neuronal survival and axon regeneration in mammals. Here, we assess cAMP levels and identify activated pathways in a spontaneously regenerating central nervous system. Following optic nerve crush in goldfish, almost all retinal ganglion cells (RGC) survive and regenerate retinotectal topography. Goldfish received injections of a cAMP analogue (CPT-cAMP), a protein kinase A (PKA) inhibitor (KT5720), both compounds combined, or PBS (control). RGC survival in experimental groups was unaffected at any stage. The rate of axon regeneration was accelerated by the activator and decelerated both by the inhibitor and by combined injections, suggesting a PKA-dependent pathway. In addition, errors in regenerate retinotectal topography were observed when agents were applied in vivo and RGC response to the guidance cue ephrin-A5 in vitro was altered by the inhibitor. Our results highlight that therapeutic manipulation of cAMP levels to enhance axonal regeneration in mammals must ensure that topography, and consequently function, is not disrupted.

Radiation-induced proliferation of the human A431 squamous carcinoma cells is dependent on EGFR tyrosine phosphorylation

Accelerated cellular repopulation has been described as a response of tumors to fractionated irradiation in both normal tissue and tumor systems. To identify the mechanisms by which cells enhance their proliferative rate in response to clinically used doses of ionizing radiation (IR) we have studied human mammary and squamous carcinoma cells which are autocrine growth regulated by the epidermal growth factor receptor (EGFR) and its ligands, transforming growth factor-alpha and EGF. Both EGF and IR induced EGFR autophosphorylation, comparable levels of phospholipase C gamma activation as measured by inositol-1,4,5-triphosphate production, and as a consequence oscillations in cytosolic [Ca2+]. Activities of Raf-1 and mitogen-activated protein kinase (MAPK) were also stimulated by EGF and IR by Ca(2+)-dependent mechanisms. All these responses to EGF and IR were dependent upon activation of EGFR as judged by the use of the specific inhibitor of EGFR autophosphorylation, tyrphostin AG1478. Importantly, IR-induced proliferation of A431 cells was also inhibited by AG1478. This is the first report which demonstrates a link between IR-induced activation of proliferative signal transduction pathways and enhanced proliferation. We propose that accelerated repopulation of tumors whose growth is regulated by EGFR is initiated by an IR-induced EGFR activation mechanism that mimics the effects of growth factors.

Host responses induced by co-infection with Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans in a murine model

In this study, evidence is presented that mixed infection with the periodontal pathogens Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans results in a synergistic effect in their pathogenicity and in their ability to induce humoral and cellular host responses. BALB/c mice were injected subcutaneously on the back with P. gingivalis ATCC 53977, A. actinomycetemocomitans 75 or a mixture of both bacteria. Samples of blood and fluid from abscesses formed at the site of injection (first degree) or distant from the injection site were collected for microbiologic analysis. Serum and spleens were obtained for evaluation of humoral and cellular responses to P. gingivalis and A actinomycetemocomitans. Mice injected with A. actinomycetemcomitans had first-degree lesions only, whereas mice injected with P. gingivalis and A. actinomycetemcomitans had lesions at first- and second-degree sites from which both bacterial species were isolated. A serum anti-P. gingivalis response was induced in P. gingivalis-injected mice, which was higher in mice injected with P. gingivalis and A. actinomycetemcomitans. This pattern was not seen in the anti-A, actinomycetemcomitans response. Lymphoproliferative responses to phytohemagglutinin, Escherichia coli lipopolysaccharide and P. gingivalis of spleen cells from infected mice were decreased, especially following co-infection. Furthermore, co-infection of mice resulted in the greatest decrease in the number of CD5+, especially CD4+ lymphocytes.

Modification of experimental Porphyromonas gingivalis murine infection by immunization with a polysaccharide-protein conjugate

To better understand the role of the capsular polysaccharide in the virulence of Porphyromonas gingivalis, the effect of immunization with a polysaccharide-protein conjugate on experimental murine infection was evaluated. The conjugate was prepared using polysaccharide isolated from P. gingivalis strain ATCC 53977 and bovine serum albumin. One group of 22 mice was immunized by intraperitoneal injection with the conjugate and a control group of 25 mice was similarly immunized with bovine serum albumin. Serum antibody reactive to the polysaccharide, as determined by enzyme-linked immunosorbent assay, was elevated in the group of mice immunized with the polysaccharide-protein conjugate but not in the mice immunized with bovine serum albumin. Both groups of mice were challenged with P. gingivalis strain ATCC 53977 (10(10) cells) administered subcutaneously on the dorsal surface. Following challenge, the mice immunized with the polysaccharide-protein conjugate appeared healthier and demonstrated less weight loss than did the control group of mice. Ulcerative lesions at secondary locations were smaller in mice immunized with the polysaccharide-protein conjugate. Thus, immunization of mice with a conjugate containing P. gingivalis polysaccharide could reduce the severity of but not prevent an invasive infection with P. gingivalis.

Experimental Porphyromonas gingivalis infection in nonimmune athymic BALB/c mice

The purpose of this report was to study the role of T lymphocytes following injection of Porphyromonas gingivalis in a mouse abscess model. Three invasive P. gingivalis isolates (ATCC 53977, W83, and AJW4) were injected into athymic BALB/c mice and their heterozygous (nu/+) littermates. The athymic BALB/c (nu/nu) mice were able to localize the invasive P. gingivalis isolates at the injection site. By comparison, the heterozygous BALB/c (nu/+) littermates developed hemorrhagic secondary lesions within 24 h after subcutaneous injection of the same invasive P. gingivalis isolates. These results suggest that naive T lymphocytes may contribute to the pathology associated with P. gingivalis infection.

Analysis of in vitro lymphoproliferative responses and antibody formation following subcutaneous injection of Actinobacillus actinomycetemcomitans and Wolinella recta in a murine model

The potential of Wolinella recta and Actinobacillus actinomycetemcomitans to cause abscesses and induce an immune response was tested in BALB/c mice. Mice were injected subcutaneously with W. recta, A. actinomycetemcomitans or a mixture of these 2 microorganisms. Mice injected with A. actinomycetemcomitans alone, or with both organisms, demonstrated abscesses at the injection site 2 days later, from which pure cultures of A. actinomycetemcomitans were isolated. Mice injected with W. recta had small, flat abscesses at the injection site from which no bacteria could be cultured. W. recta was cultured from injection sites only when associated with A. actinomycetemcomitans. Mice developed positive serum IgG antibody responses to W. recta by 20 days post-injection but not to A. actinomycetemcomitans whether injected in pure culture or mixed infection. In vitro lymphoproliferative responses following injection of W. recta and/or A. actinomycetemcomitans resulted in increased lymphocyte reactivity in unstimulated cultures and decreased in vitro responses to phytohemagglutinin. In vitro lymphoproliferative responses to Escherichia coli LPS or Salmonella typhimurium LPS were depressed in mice injected with A. actinomycetemcomitans, but not in mice injected with W. recta.

Heterogeneity of virulence among strains of Bacteroides gingivalis

The ability of fresh isolates of B. gingivalis to establish abscesses in the mouse model was studied by comparing them with established laboratory strains of B. gingivalis. Eight fresh isolates obtained from plaque associated with periodontal disease and grown under similar conditions as established strains were injected subcutaneously on the back of the mouse. All of these strains produced secondary lesions on the abdomen. Septicemia was associated with seven of the strains. Two commonly used laboratory strains, W50 and W83, also produced secondary lesions and septicemia. Five other laboratory strains produced only localized abscesses. On histologic examination, the strains that produced disseminated disease showed invasion of connective disease by individual bacteria that were not in clumps. The strains that produced localized abscesses were characterized by growing in colonies or clumps in the abscess cavity. Four synthetic enzyme substrates were examined to determine whether the differences between invasive and non-invasive strains were due to differences in proteolytic enzyme production. No differences in enzyme production could be demonstrated with the selected substrates.

IL-2-induced polyclonal proliferation of human peripheral blood lymphocytes: functional and phenotypic characteristics of proliferating cells

Unstimulated human peripheral blood lymphocytes (HPBL) were found to proliferate when cultured in vitro with interleukin-2 (IL-2). In bulk long-term cultures of HPBL cultured with IL-2, cell numbers usually doubled after 8-11 days of culture, and a 10-fold increase in cell number occurred between the second and third weeks of culture. These cells retained their ability to respond to a panel of T-cell dependent antigens, phytomitogens and allogeneic cells up to Day 21 of culture. The proliferating cells predominantly expressed the T-cell antigens (CD3, CD4 and CD8), but not antigens of natural killer (NK) cells, B cells or mononuclear phagocytic cells. The proportion of cells expressing CD3 and CD4 antigens progressively increased with length of culture. Purified lymphocytes expressing either CD4 or CD8 antigens were also found to be capable of showing a proliferative response to IL-2, especially when provided with autologous accessory cells. However, purified human peripheral blood B cells expressing the Leu 12 antigen did not respond with or without autologous accessory cells. Unlike the responses to phytomitogen, soluble antigens or allogeneic cells, the proliferative responses of HPBL to IL-2 were not inhibited by a monoclonal antibody (OK-Ia-1) to the non-polymorphic part of human class II histocompatibility antigens.

Monoclonal antibody for identification of Bacteroides gingivalis lipopolysaccharide

A monoclonal antibody, BBG-25, raised in BALB/c mice demonstrated specificity for Bacteroides gingivalis lipopolysaccharide. Immunoblotting indicated that this monoclonal antibody does not cross-react with lipopolysaccharide prepared from enterobacterial organisms or from other Bacteroides species.

Effect of immunization on experimental Bacteroides gingivalis infection in a murine model

BALB/c mice were immunized with an invasive (A7A1-28) or noninvasive (381) Bacteroides gingivalis strain, Bacteroides intermedius, or Ringer solution. All immunized mice were subsequently challenged with the invasive B. gingivalis strain and examined for septicemia or secondary spread of the infection or both. Mice immunized with the invasive B. gingivalis strain localized the infection to the challenge site. Mice immunized with the noninvasive B. gingivalis strain, B. intermedius, or Ringer solution developed spreading infections. These data suggest that immunization with an invasive B. gingivalis strain can alter the course of subsequent infections.

Activation and long-term proliferation of human cord blood T cells with human recombinant interleukin-2

We report here the results of in vitro studies that demonstrate that purified human recombinant interleukin-2 (hrIL-2) is a potent stimulant for freshly isolated cord blood lymphocytes of healthy full-term infants. Different culture parameters were studied to define the optimal conditions for eliciting maximal levels of activation. Highest levels of hrIL-2-induced TdR[3H] uptake were recorded on day 7 for cultures containing 100 U hrIL-2/ml. Results of comparative studies demonstrated that the reactivity of cord blood lymphocytes to hrIL-2 was equal to, if not greater than, that of healthy adult lymphocytes. Cord blood cells that had been activated with hrIL-2 could be propagated in long-term (greater than 30 days) cultures as hrIL-2-dependent lines, and these lines could be initiated with a high degree of success. Phenotypic analysis was performed using different monoclonal antibodies and cytofluorometry, and studies characterizing cells of the long-term lines have shown that they consisted of a heterogenous population of T4 helper and T8 cytotoxic/suppressor cells; in some instances, natural killer (NK) cells were also present. Other experiments demonstrated that hrIL-2-activated and hrIL-2-propagated T cells expressed the IL-2 receptor (IL-2R; defined by monoclonal antibody anti-Tac) and the number of IL-2-R-positive cells could be increased two-fold or more by exposing the cells to a phorbol ester. This report provides additional information to support the hypothesis that hrIL-2 not only sustains T cell proliferation (i.e., second signal) but also induces T cell activation (i.e., first signal).(ABSTRACT TRUNCATED AT 250 WORDS)

Elevation of serum IgG levels and normalization of T4/T8 ratio after hepatitis in a patient with common variable hypogammaglobulinemia

Acute hepatitis infection developed in a 47-year-old male patient with common variable hypogammaglobulinemia as a consequence of plasma transfusion therapy. Coincident with increases in serum transaminase activities indicative of acute hepatitis, serum IgG levels continued to rise to 506 mg/dl. When plasma replacement therapy was stopped, a transient decline in IgG level (to 371 mg/dl) was produced, followed by a sharp increase in IgG to 607 mg/dl. During this period, the patient's T4/T8 ratio, which had been inverted (0.89), exhibited significant normalization to 1.57. Nevertheless, the patient failed to produce specific antibody after immunization with a number of defined antigens. The mechanism whereby this presumed non-A, non-B hepatitis augmented endogenous IgG production in this patient remains unknown but may be related to diminished suppressor T cell activity. The patient's inability to produce specific antibody during this period suggests an underlying defect in one or more lymphocyte subsets involved in either helper T cell activity and/or immunologic memory.

Defective differentiation of natural killer cells in SJL mice. Role of the thymus

As previously shown, three distinct phenotypes exist in murine natural killer (NK) cell activity when it is evaluated by the endogenous levels of activity and the susceptibility to augmentation by interferon (IFN) and IFN inducers. The "low" phenotype has low levels of activity which can be poorly augmented by IFN, as in mice of SJL strain. The "inducible" phenotype exhibits low endogenous levels but can vigorously respond to IFN-mediated augmentation, as in A.SW strain. The "high" NK phenotype shows high levels of endogenous activity which can be augmented to still higher levels by IFN, as in B10.S mice. Since SJL mice with congenital absence of the thymus (nude) were of the inducible type, the effect of neonatal thymectomy was examined in the present study. Neonatal thymectomy was found to convert the low phenotype of SJL mice to the inducible, mimicking the effect of nu/nu genotype. Thymectomy as late as 25 days after birth was effective, but retransplantation of a syngeneic newborn or adult thymus, or thymocytes, failed to reverse the effect of thymectomy. The poor responsiveness of NK activity to IFN in SJL, therefore, is extrinsic to the NK cell lineage and is attributable to suppression or maturational block of NK cell differentiation by the thymus during the first few weeks of neonatal life. A series of experiments with bone marrow chimeras showed that the SJL recipients did not allow the expression of inducible or high phenotype by bone marrow progenitors from allogeneic donors with either phenotype. Therefore, the SJL recipients provide an environment which suppresses not only the development of IFN-sensitive NK cell precursors, but also the levels of endogenous NK cell activity. SJL bone marrow cells gave rise to NK activity of inducible phenotype in B10.S recipients, confirming the crucial role of the environment in which NK cell differentiation takes place.

Defective differentiation of natural killer cells in SJL mice. Role of the thymus

As previously shown, three distinct phenotypes exist in murine natural killer (NK) cell activity when it is evaluated by the endogenous levels of activity and the susceptibility to augmentation by interferon (IFN) and IFN inducers. The "low" phenotype has low levels of activity which can be poorly augmented by IFN, as in mice of SJL strain. The "inducible" phenotype exhibits low endogenous levels but can vigorously respond to IFN-mediated augmentation, as in A.SW strain. The "high" NK phenotype shows high levels of endogenous activity which can be augmented to still higher levels by IFN, as in B10.S mice. Since SJL mice with congenital absence of the thymus (nude) were of the inducible type, the effect of neonatal thymectomy was examined in the present study. Neonatal thymectomy was found to convert the low phenotype of SJL mice to the inducible, mimicking the effect of nu/nu genotype. Thymectomy as late as 25 days after birth was effective, but retransplantation of a syngeneic newborn or adult thymus, or thymocytes, failed to reverse the effect of thymectomy. The poor responsiveness of NK activity to IFN in SJL, therefore, is extrinsic to the NK cell lineage and is attributable to suppression or maturational block of NK cell differentiation by the thymus during the first few weeks of neonatal life. A series of experiments with bone marrow chimeras showed that the SJL recipients did not allow the expression of inducible or high phenotype by bone marrow progenitors from allogeneic donors with either phenotype. Therefore, the SJL recipients provide an environment which suppresses not only the development of IFN-sensitive NK cell precursors, but also the levels of endogenous NK cell activity. SJL bone marrow cells gave rise to NK activity of inducible phenotype in B10.S recipients, confirming the crucial role of the environment in which NK cell differentiation takes place.