Orna Tighe

Phenotypic characterization of spatial cognition and social behavior in mice with 'knockout' of the schizophrenia risk gene neuregulin 1.

Neuregulin-1 (NRG1) has been identified as a candidate susceptibility gene for schizophrenia. In the present study the functional role of the NRG1 gene, as it relates to cognitive and social processes known to be disrupted in schizophrenia, was assessed in mice with heterozygous deletion of transmembrane (TM)-domain NRG1 in comparison with wildtypes (WT). Social affiliative behavior was assessed using the sociability and preference for social novelty paradigm, in terms of time spent in: (i) a chamber containing an unfamiliar conspecific vs. an empty chamber (sociability), or (ii) a chamber containing an unfamiliar conspecific vs. a chamber containing a familiar conspecific (preference for social novelty). Social dominance and aggressive behavior were examined in the resident-intruder paradigm. Spatial learning and memory were assessed using the Barnes maze paradigm, while spatial working memory was measured using the continuous variant of the spontaneous alternation task. Barnes maze data revealed intact spatial learning in NRG1 mutants, with elevated baseline latency to enter the escape hole in male NRG1 mutants reflecting an increase in activity level. Similarly, although a greater number of overall arm entries were found, spontaneous alternation was unaffected in NRG1 mice. Social affiliation data revealed NRG1 mutants to evidence a specific loss of WT preference for spending time with an unfamiliar as opposed to a familiar conspecific. This suggests that NRG1 mutants show a selective impairment in response to social novelty. While spatial learning and working memory processes appear intact, heterozygous deletion of TM-domain NRG1 was associated with disruption to social novelty behavior. These data inform at a novel phenotypic level on the functional role of this gene in the context of its association with risk for schizophrenia.

Gene expression differences between the microsatellite instability (MIN) and chromosomal instability (CIN) phenotypes in colorectal cancer revealed by high-density cDNA array hybridization.

Two distinct pathways of tumorigenesis exist in sporadic colorectal cancer. The microsatellite instability pathway (MIN), which is characterized by widespread microsatellite instability due to aberrant mismatch repair machinery, accounts for 15% of all sporadic colorectal cancers. The chromosomal instability (CIN) phenotype, which accounts for 85% of sporadic colorectal cancers, is characterized by gross chromosomal lesions but the underlying mechanism remains unclear. We have addressed differences in gene expression between the MIN and CIN colorectal cancer phenotypes in vitro by the use of high density cDNA filters to compare gene expression patterns between MIN and CIN colorectal cancer cell-lines yielding a panel of 73 consistently differentially expressed genes. Nine of these genes were subjected to confirmatory analysis by independent methods, of which six were confirmed as being differentially expressed; PLK, RanBP2 and CCNA2 were overexpressed in CIN lines while BTF3, H2AZ and PTPD1 were overexpressed in MIN lines. These six genes are involved in diverse processes, such as maintenance of chromatin architecture, DNA-damage checkpoint and cell cycle regulation, which may contribute to the CIN and MIN phenotypes.

Phenotypic characterization of cognition and social behavior in mice with heterozygous versus homozygous deletion of catechol-O-methyltransferase

Catechol-O-methyltransferase is an important enzyme in the metabolism of dopamine and an important regulator of aspects of dopamine-dependent working memory in prefrontal cortex that are disturbed in schizophrenia. This study investigated the phenotype of mice with heterozygous deletion vs. homozygous knockout of the catechol-O-methyltransferase gene across paradigms that access processes relevant for psychotic illness. Homozygotes evidenced improved performance in spontaneous alternation, an index of immediate spatial working memory; this effect appeared more substantive in males and was reflected in performance in aspects of the Barnes maze, an index of spatial learning/memory. Heterozygotes evidenced impaired performance in object recognition, an index of recognition memory; this effect was evident for both sexes at a retention interval of 5 min but appeared more enduring in males. There were no material effects for either genotype in relation to sociability or social novelty preference. While homozygous catechol-O-methyltransferase deletion results in improvement in spatial learning/working memory with little effect on social behavior, heterozygous deletion results in impairment of recognition memory. We have reported recently, using similar methods, that mice with deletion of the schizophrenia risk gene neuregulin-1 evidence disruption to social behavior, with little effect on spatial learning/working memory. The data suggest that catechol-O-methyltransferase and neuregulin-1 may influence, respectively, primarily cognitive and social endophenotypes of the overall schizophrenia syndrome.

Chronic Adolescent Exposure to Δ-9-Tetrahydrocannabinol in COMT Mutant Mice: Impact on Psychosis-Related and Other Phenotypes

Cannabis use confers a two-fold increase in the risk for psychosis, with adolescent use conferring even greater risk. A high–low activity catechol-O-methyltransferase (COMT) polymorphism may modulate the effects of adolescent Δ-9-tetrahydrocannabinol (THC) exposure on the risk for adult psychosis. Mice with knockout of the COMT gene were treated chronically with THC (4.0 and 8.0 mg/kg over 20 days) during either adolescence (postnatal days (PDs) 32–52) or adulthood (PDs 70–90). The effects of THC exposure were then assessed in adulthood across behavioral phenotypes relevant for psychosis: exploratory activity, spatial working memory (spontaneous and delayed alternation), object recognition memory, social interaction (sociability and social novelty preference), and anxiety (elevated plus maze). Adolescent THC administration induced a larger increase in exploratory activity, greater impairment in spatial working memory, and a stronger anti-anxiety effect in COMT knockouts than in wild types, primarily among males. No such effects of selective adolescent THC administration were evident for other behaviors. Both object recognition memory and social novelty preference were disrupted by either adolescent or adult THC administration, independent of genotype. The COMT genotype exerts specific modulation of responsivity to chronic THC administration during adolescence in terms of exploratory activity, spatial working memory, and anxiety. These findings illuminate the interaction between genes and adverse environmental exposures over a particular stage of development in the expression of the psychosis phenotype.

Schizophrenia-related endophenotypes in heterozygous neuregulin-1 'knockout' mice.

Neuregulin‐1 (NRG1) has been shown to play a role in glutamatergic neurotransmission and is a risk gene for schizophrenia, in which there is evidence for hypoglutamatergic function. Sensitivity to the behavioural effects of the psychotomimetic N‐methyl‐d‐aspartate receptor antagonists MK‐801 and phencyclidine (PCP) was examined in mutant mice with heterozygous deletion of NRG1. Social behaviour (sociability, social novelty preference and dyadic interaction), together with exploratory activity, was assessed following acute or subchronic administration of MK‐801 (0.1 and 0.2 mg/kg) or PCP (5 mg/kg). In untreated NRG1 mutants, levels of glutamate, N‐acetylaspartate and GABA were determined using high‐performance liquid chromatography and regional brain volumes were assessed using magnetic resonance imaging at 7T. NRG1 mutants, particularly males, displayed decreased responsivity to the locomotor‐activating effects of acute PCP. Subchronic MK‐801 and PCP disrupted sociability and social novelty preference in mutants and wildtypes and reversed the increase in both exploratory activity and social dominance‐related behaviours observed in vehicle‐treated mutants. No phenotypic differences were demonstrated in N‐acetylaspartate, glutamate or GABA levels. The total ventricular and olfactory bulb volume was decreased in mutants. These data indicate a subtle role for NRG1 in modulating several schizophrenia‐relevant processes including the effects of psychotomimetic N‐methyl‐d‐aspartate receptor antagonists.

Conservation of behavioural topography to dopamine D1-like receptor agonists in mutant mice lacking the D1A receptor implicates a D1-like receptor not coupled to adenylyl cyclase

Though D1-like dopamine receptors [D1A/B] are defined in terms of linkage to the stimulation of adenylyl cyclase, with D1A assumed to be the functionally prepotent subtype, evidence suggests the existence of another, novel D1-like receptor without such coupling. To investigate these issues we challenged mutant mice having targeted gene deletion of the D1A receptor with selective agonists and used an ethologically-based assessment technique to resolve resultant behavioural topography. D1-like-dependent behaviour was substantially conserved in D1A-null mice relative to wild-types following challenge with each of two selective D1-like agents: A 68930 (0.068-2.0 mg/kg s.c.) which exhibits full efficacy to stimulate adenylyl cyclase, and SKF 83959 (0.016-2.0 mg/kg s.c.) which fails to stimulate adenylyl cyclase, and indeed inhibits the stimulation of adenylyl cyclase induced by dopamine. Furthermore, responsivity to the selective D2-like agonist RU 24213 (0.1-12.5 mg/kg s.c.) was conserved in D1A-null mice, indicating the integrity of D1-like:D2-like interactions at the level of behaviour. These data are consistent with behavioural primacy of a D1-like receptor other than D1A [or D1B] that is coupled to a transduction system other than/additional to adenylyl cyclase.

Serial analysis of gene expression identifies putative metastasis-associated transcripts in colon tumour cell lines

We have used serial analysis of gene expression (SAGE) to identify gene expression differences between a primary colon tumour cell line (SW480) and an isogenic lymph-node metastasis cell line (SW620). Differential expression was confirmed for the following genes: keratin K5, cystatin S, serum amyloid A, the human homologue of yeast ribosomal S28 and the p32 subunit of human pre-mRNA splicing factor SF2. Expression of confirmed differences were also analysed in other metastatic cell lines.

Genetic basis of transferase-deficient galactosaemia in Ireland and the population history of the Irish Travellers

Transferase-deficient galactosaemia, resulting from deficient activity of galactose-1-phosphate uridyltransferase (GALT), is relatively common among the Travellers, an endogamous group of commercial/industrial nomads within the Irish population. This study has estimated the incidence of classical transferase-deficient galactosaemia in Ireland and determined the underlying GALT mutation spectrum in the Irish population and in the Traveller group. Based upon a survey of newborn screening records, the incidence of classical transferase-deficient galactosaemia was estimated to be 1 in 480 and 1 in 30 000 among the Traveller and non-Traveller communities respectively. Fifty-six classical galactosaemic patients were screened for mutation in the GALT locus by standard molecular methods. Q188R was the sole mutant allele among the Travellers and the majority mutant allele among the non-Travellers (89.1%). Of the five non-Q188R mutant alleles in the non-Traveller group, one was R333G and one F194L with three remaining uncharacterised. Anonymous population screening has shown the Q188R carrier frequency to be 0.092 or 1 in 11 among the Travellers as compared with 0.009 or 1 in 107 among the non-Travellers. The Q188R mutation was shown to be in linkage disequilibrium with a Sac I RFLP flanking exon 6 of the GALT gene. This represents the first molecular genetic description of classical transferase-deficient galactosaemia in Ireland and raises intriguing questions concerning the genetic history of the Irish Travellers.

Phenotypic effects of repeated psychosocial stress during adolescence in mice mutant for the schizophrenia risk gene neuregulin-1: a putative model of gene×environment interaction

There is a paucity of animal models by which the contributions of environmental and genetic factors to the pathobiology of psychosis can be investigated. This study examined the individual and combined effects of chronic social stress during adolescence and deletion of the schizophrenia risk gene neuregulin-1 (NRG1) on adult mouse phenotype. Mice were exposed to repeated social defeat stress during adolescence and assessed for exploratory behaviour, working memory, sucrose preference, social behaviour and prepulse inhibition in adulthood. Thereafter, in vitro cytokine responses to mitogen stimulation and corticosterone inhibition were assayed in spleen cells, with measurement of cytokine and brain-derived neurotrophic factor (BDNF) mRNA in frontal cortex, hippocampus and striatum. NRG1 mutants exhibited hyperactivity, decreased anxiety, impaired sensorimotor gating and reduced preference for social novelty. The effects of stress on exploratory/anxiety-related parameters, spatial working memory, sucrose preference and basal cytokine levels were modified by NRG1 deletion. Stress also exerted varied effect on spleen cytokine response to concanavalin A and brain cytokine and BDNF mRNA expression in NRG1 mutants. The experience of psychosocial stress during adolescence may trigger further pathobiological features that contribute to the development of schizophrenia, particularly in those with underlying NRG1 gene abnormalities. This model elaborates the importance of gene × environment interactions in the etiology of schizophrenia.

Congenic D1A dopamine receptor mutants: ethologically based resolution of behavioural topography indicates genetic background as a determinant of knockout phenotype.

D1A-null mice were backcrossed over 14 generations into a C57BL/6 background to result in essential elimination (to <0.005%) of any contribution from the 129/Sv component of their initially mixed (129/Sv×C57BL/6) background. Their phenotype was assessed using an ethologically based approach that resolves each individual topography of behaviour in the natural repertoire. Habituation of sniffing, locomotion, rearing seated, and rearing to wall in wild types over several hours was profoundly retarded in congenic D1A mutants; conversely, rearing free and sifting were essentially abolished. Resultant increases in individual topographies of behaviour were substantially greater in congenic D1A mutants than in those on a mixed background. This phenotype was little altered by the selective D1-like antagonist SCH 23390 and could not be blocked by the selective D2-like antagonist YM 09151-2. The selective D1-like agonist SK&F 83959 could not further elevate those behaviours already heightened in congenic D1A mutants, while the induction of stereotyped sniffing and plodding locomotion by the selective D2-like agonist RU 24213 was disrupted. Genetic background appears to modulate critically the magnitude but not the general nature of the D1A-null phenotype, which may involve compensatory processes independent of other D1-like or D2-like receptors.