Testing linkage hypothesis in hybrid analysis of alternatively distributed behavioral traits with incomplete penetrance

The use of polymorphic microsatellite markers for mapping alternatively distributed behavioral traits with incomplete penetrance was studied with special reference to inheritance of predisposition to catalepsy in mice. Using only backcrosses as a segregating population, the major gene for catalepsy was with high likelihood mapped to region 30-75 cM of murine chromosome 13. It was also established that this gene determines 20% of the trait penetrance whereas the remaining 31% of the observed penetrance are accounted for by numerous polygenes.     

Genetic relationship of catalepsy to penduliform movements and audiogenic epilepsy in rats

Within outbred Wistar stock, the pendulum movements are found to be inherited in what may be considered as a dominant mono- or oligogenic mode of inheritance with incomplete penetrance. This indicates that the albinism only permits the manifestation of the pendulum movements, which are also controlled by some other gene or genes. The pendulum movements show a positive genetic relation to catalepsy, although this relation is not strong: the proportion of animals with pendulum movements is 23% in the control population and 32% in F12-F16 bred for catalepsy (p less than 0.05). Within the latter, the proportion of animals with pendulum movements was 43% in the progeny of parents with phenotypically expressed catalepsy, and 29% in the progeny of phenotypically "normal" animals (p less than 0.01). The frequency of audiogenic seizures was 32% in the control population and 17% in F8-F16 bred for catalepsy (p less than 0.001). A genetic model is proposed to account for the paradoxical situation, where pendulum movements have a positive genetic relation both to catalepsy and audiogenic epilepsy, the catalepsy being at the same time negatively related to epilepsy.     

Relationship between certain forms of catalepsy in rats. An attempt at genetic analysis]

Rats from strain GC selected for predisposition to "pseudocatalepsy" (a cataleptic response to an enforced vertical posture) are also characterized by an increased duration of pinch-induced catalepsy. Expression of catalepsy in F1 and segregation in F2 hybrids obtained from GC x Wistar crossing were analyzed. The results obtained indicate that a monogenic dominant inheritance with incomplete penetrance cannot be ruled out for both pseudocatalepsy and pinch-induced catalepsy.     

Selective breeding for catalepsy changes the distribution of microsatellite D13Mit76 alleles linked to the 5-HT serotonin receptor gene in mice

Catalepsy (pronounced motor inhibition) is a natural defensive reaction against predator. Recently, the quantitative trait locus for catalepsy was mapped on mouse chromosome 13 near the 5-HT(1A) serotonin receptor gene. Here, the linkage between catalepsy and the 5-HT(1A) receptor gene was verified using breeding experiment. Selective breeding for high predisposition to catalepsy was started from backcross BC[CBA x (CBA x AKR)] generation between catalepsy-prone (CBA) and catalepsy-resistant (AKR) mouse strains. CBA and AKR strains also differed in the 5-HT(1A) receptor functional activity. A rapid increase of cataleptic percentage from 21.2% in the backcrosses to 71% in the third generation of selective breeding (S3) was shown. The fragment of chromosome 13 including the 5-HT(1A) receptor gene was marked with D13Mit76 microsatellite. Breeding for catalepsy increased the concentration of CBA-derived and decreased the concentration of AKR-derived alleles of microsatellite D13Mit76 in the S1 and S2. All mice of the S9 and S12 were homozygous for CBA-derived allele of D13Mit76 marker. Mice of the S12 showed CBA-like receptor activity. These findings indicate that selective breeding for behavior can involve selection of polymorphic variants of the 5-HT(1A) receptor gene.     

Genetic relationships between catalepsy and pendulum movements in rats]

Predispositions to pendulum movements (PMs) and catalepsy was studied in rat strains selected for predisposition to catalepsy and for enhanced or suppressed PMs. Positive correlation between PMs and catalepsy at earlier stages of selection changed to negative at later stages. Based on these data, it was hypothesized that the genes that determine the predisposition to catalepsy affect the expression of the gene determining PMs in such a way that different PM alleles become dominant in the cases of moderate and strong effects of the catalepsy genes.     

The role of 5‐HT2A receptor and 5‐HT2A/5‐HT1A receptor interaction in the suppression of catalepsy

In the present study, the 5‐HT_2A and 5‐HT_1A receptors functional activity and 5‐HT_2A receptor gene expression were examined in the brain of ASC/Icg and congenic AKR.CBAD13Mit76C mouse strains (genetically predisposed to catalepsy) in comparison with the parental catalepsy‐resistant AKR/J and catalepsy‐prone CBA/Lac mouse strains. The significantly reduced 5‐HT_2A receptor functional activity along with decreased 5‐HT_2A receptor gene expression in the frontal cortex was found in all mice predisposed to catalepsy compared with catalepsy‐resistant AKR/J. 5‐HT_2A agonist DOI (0.5 and 1 mg/kg, i.p.) significantly reduced catalepsy in ASC/Icg and CBA/Lac, but not in AKR.CBAD13Mit76C mice. Essential increase in 5‐HT_1A receptor functional activity was shown in catalepsy‐prone mouse strains in comparison with catalepsy‐resistant AKR/J mice. However, in AKR.CBAD13Mit76C mice it was lower than in ASC/Icg and CBA/Lac mice. The inter‐relation between 5‐HT_2A and 5‐HT_1A receptors in the regulation of catalepsy was suggested. This suggestion was confirmed by prevention of DOI anticataleptic effect in ASC/Icg and CBA/Lac mice by pretreatment with 5‐HT_1A receptor antagonist p‐MPPI (3 mg/kg, i.p.). At the same time, the activation of 5‐HT_2A receptor led to the essential suppression of 5‐HT_1A receptor functional activity, indicating the opposite effect of 5‐HT_2A receptor on pre‐ and postsynaptic 5‐HT_1A receptors. Thus, 5‐HT_2A/5‐HT_1A receptor interaction in the mechanism of catalepsy suppression in mice was shown.     

Genetic structure of hereditary catalepsy in mice

Catalepsy or pronounced freezing is a natural passive defense strategy in animals and a syndrome of some mental disorders in human. Hereditary catalepsy was shown to be associated with depressive-like features in rats and mice. The loci underlying the difference in predisposition to catalepsy between catalepsy-prone CBA/lacJ and catalepsy-resistant AKR/J mice were mapped using congenic line and selective breeding approaches. Three congenic mouse lines (AKR.CBA-D13Mit76C, AKR.CBA-D13Mit76A and AKR.CBA-D13Mit78) carrying the 59- to 70-, 61- to 70- and 71- to 75-c m fragments of chromosome 13 transferred from the CBA to the AKR genome were created by nine successive backcrossing of (CBA × AKR)F₁ on AKR strain. Because catalepsy was found only in the AKR.CBA-D13Mit76C and AKR.CBA-D13Mit76A mice, the major gene of catalepsy was mapped on the fragment of 61–70 c m . Selective breeding of the (CBA × (CBA × AKR))BC backcross generation for high predisposition to catalepsy showed numerous genome-wide distributed CBA-derived alleles as well as the AKR-derived alleles mapped on chromosome 17 and on the proximal parts of chromosomes 10 and 19 that increased the cataleptogenic effect of the major gene.     

Gametic imprinting and expression of the gene Fused in the house mice

The discovery of the gametic imprinting phenomena in mammals makes it possible to have a new look at some facts concerning the expression and inheritance of genes with variable penetrance. Fused (Fu) is a dominant mutation located on chromosome 17, one of the few examples uses to demonstrate gametic imprinting in mice. This mutation has maternal effect connected with decrease in its penetrance. It was shown that t12 haplotype significantly reduces penetrance of the Fu in the progeny of Fu/t12 females. The results of reciprocal crosses of heterozygotes for t12 haplotypes indicate that penetrance of maternal Fu gene is reduced. Far more strong influence on the fused penetrance have the dominant suppressors, located beyond the chromosome 17. The penetrance of the fused gene decreases in that case up to 8-17%. Results of the experiments show strong influence of gametic pathway on penetrance of the gene by which the gene is transmitted to the next generation. The results also made it possible to describe the regularities of gametic imprinting. This phenomenon clearly indicates the existence of gametic and zygotic ontogenetic phases. According to the hypothesis proposed gametic phase of ontogenesis in mammals starts after initialization, i. e. after a process of chromosome erasing from epigenetic information and preparing to enter the next ontogenetic cycle.     

Association of glycoprotein gp130 with hereditary catalepsy in mice

Glycoprotein gp130 is involved in the interleukin‐6 (IL‐6) and related cytokines' signaling. Linkage between the gp130 coding gene and freezing reaction (catalepsy) was shown. Here, we compared the expression and function of the gp130 in male mice of catalepsy‐resistant AKR/J strain and catalepsy‐prone congenic AKR.CBA‐D13Mit76 strain created by transferring the gp130 gene allele from catalepsy‐prone CBA/Lac to the genome of AKR/J strain. No difference in the gp130 expression in the frontal cortex, hippocampus and midbrain between AKR and AKR.CBA‐D13Mit76 mice was found. However, AKR.CBA‐D13Mit76 mice were more sensitive to bacterial lipopolysaccharide (LPS). The administration of LPS (50 µg/kg, ip) significantly increased mRNA level of the gene coding IL‐6‐regulated glial fibrillary acidic protein (GFAP) in the midbrain, induced catalepsy and decreased locomotion in the open field and social investigation tests in AKR.CBA‐D13Mit76, but not in AKR mice. The result indicates (1) the association between gp130 and hereditary catalepsy, (2) increased functional activity rather than expression of gp130 in AKR.CBA‐D13Mit76 mice and (3) the involvement of gp130 in the mechanism of LPS‐induced alteration of behavior.     

Hereditary Catalepsy: Genetic and Molecular Mechanisms of Catalepsy in Mice

The results of experiments on the inheritance and neurobiological mechanism of high predisposition to tonic immobility (catalepsy) in CBA mice are discussed. Genetic analysis has demonstrated a monogenic inheritance of the predisposition to catalepsy. A set of polymorphic microsatellite markers has been used to demonstrate that the predisposition to catalepsy is linked to the distal fragment of mouse chromosome 13, which contains the gene of the 5-HT_1A serotonin receptor. Pharmacological and biochemical evidence for the association between hereditary catalepsy and 5-HT_1A receptor dysfunction are presented. The use of CBA mice for studying the mechanisms of depression and the effects of antidepressants is discussed.     

History dependent effects on phenotypic expression of a newly emerged gene

In this study, we investigate the history dependence of the penetrance of a newly emerged gene. Penetrance is defined as the percentage of individuals with a given genotype who exhibit the phenotype associated with that particular genotype. Here, we used the glutamine synthetase gene and its mutants with lower fitness as model genes. They were introduced into host cells of Escherichia coli deprived of the gene, and their penetrance was measured using the host having a different history: either with or without glutamine starvation. Results show that for all genes tested, the value of penetrance was higher when they were introduced into the host cell without starvation than that when introduced into the starved cell, demonstrating the history dependence of the penetrance of a newly emerged gene. In addition, genes with lower fitness showed lower penetrance, and the effect of the difference in fitness on gene penetrance also depended on the history of the host cell.     

The two locus control of Leber hereditary optic neurophathy and a high penetrance in Japanese pedigrees

The maternal transmission of Leber hereditary optic neuropathy (LHON) can be explained by the mitochondrial DNA mutation. However, the characteristic mode of inheritance, i.e. male predominance and reduced penetrance with late onset in females, suggests the simultaneous involvement of an X-linked gene in development of optic atrophy. We have assessed such a two-locus model of mitocnondrial and X-linked genes in Japanese LHON pedigrees. The goodness-of-fit test on individual male sibship data with a presumed heterozygous mother from maternal lines showed an excellent fit for the 1:1 segregation of a putative X-linked gene, thus supporting the two-locus model in the Japanese pedigrees tested. A calculated frequency of the X-linked gene was 0.10. We could not determine whether the present value is different from the reported one (= 0.08). On the other hand, the estimated penetrance for a heterozygous female was 0.196±0.039, which was about twice as high as the reported value (=0.111) with a 5% level of significance. Such a high penetrance may primarily arise from a low threshold of LHON manifestation, suggesting the ethnic difference between the LHON pedigrees in Japan and in other countries.     

Selection for the Predisposition to Catalepsy Enhances Depressive-like Traits in Mice

Immobility reaction or catalepsy is a natural passive defensive (cryptic) behavioral response to the appearance of a predator. Selection for high predisposition to catalepsy has been performed in a population of (CBA × (CBA × AKR)) backcrosses of the crossing between mouse lines prone and resistant to catalepsy (CBA and AKR, respectively). A rapid increase in the number of animals with catalepsy has been observed: from 23% in backcrosses to 71% in the S₃ generation. Selection for catalepsy does not affect mouse anxiety in the open field and plus-maze tests. However, S₈ and S₉ mice are characterized by a decreased motor activity in the open-field test and an increased immobility in the forced swim and tail suspension tests, which is interpreted as an increase in “ depressiveness.” The results indicate that genetically determined catalepsy is related to depressive-like characteristics of defensive behavior.     

Genetic analysis of the BB/W diabetic rat

A large colony of BB/W diabetic rats has been developed as a research model for insulin dependent, type 1 diabetes mellitus. The foundation stock had 8% diabetics which appeared in a sporadic manner. The Worcester (W) colony was inbred by brother X sister matings for 11 generations and the proportion of diabetics increased to over 50%. The age of detection varies from 46 to 250 days. For selection purposes, classification was made at 120 days, which means that 15 to 20% potential diabetics were classified as normal. Evidence from different analyses indicates that the inheritance of diabetes is by a recessive gene or gene cluster with 50% penetrance at 120 days. The selection of breeding stock from diabetic parents raised the proportion of diabetics produced by two normal parents from 12 to 43%. Diallel tests show that diabetic and normal offspring of two diabetic parents have the same diabetic genotype. Outcrosses to other strains of rat indicate that the trait is transferred as a recessive with only 3% diabetics recovered in the F2 where noninbred BB stock was used as the diabetic source, and 36% where partially inbred BB/W was used as the diabetic parent. Since the proportion of diabetics produced by all types of crosses has changed, and may continue to change with changes in the genetic background, we have used the operational term penetrance to describe the frequency of diabetes in individuals homozygous for the diabetes gene cluster. At present the penetrance at 120 days is 59% in the BB/W colony.     

Penetrance and expressivity of the gene for double podding in chickpea

The double-pod per peduncle trait is known to contribute to increased seed yield in chickpea (Cicer arietinum L.). A cross was made between the single-podded variety ICCV 2 and the double-podded variety JG 62 in 1993. Penetrance and expressivity of the gene for double podding was studied in an F2 population and F10 recombinant inbred lines (RILs) of this cross. Homozygous recessive allele of this gene (ss) governs the production of double flowers and pods per peduncle. Results indicated that the s allele has unstable penetrance and variable expressivity. The penetrance of this allele was 53% for the F2 and 84.5% for the RILs. The ranges for the expression of this trait among the penetrant F2 individuals and the penetrant RILs were 1.1-14.8% and 0.1-33.0%. These were 8.3-30.8% for early sown and 17.1-68.7% for the late sown double-podded parent JG 62. Thus it appears that the allele shows greater penetrance and enhanced expressivity under soil moisture stress. In the F2 the seed yield advantage of the double-podded over the single-podded plants was 18%, whereas among the RILs it was 7%. The increased number of pods and seeds contributed to the higher yield. However, there was a slight decrease in seed size of the double-podded genotypes. An increase in the size of seed may have a role in the decreased penetrance and expressivity of this allele among the double-podded segregants of the ICCV 2 x JG 62 chickpea cross.     

Selection of Wistar rats for predisposition to catalepsy

Non-inbred Wistar rats were bred for predisposition to catalepsy for 14 generations. The percentage of cataleptic rats, beginning from the F1, was about 50%, while in the control population it was about 9%. This, together with the data obtained after comparison of the proportion of cataleptic animals in the progeny from homogeneous crossings between rats of normal and cataleptic phenotypes from the group selected for catalepsy (16 and 48%, respectively), makes one suppose predisposition to catalepsy to be an oligogenic character. The later onset of stereotype-like reactions to administrations of methylphenidate, and their longer persistence in cataleptic animals points to inertness of dopaminergic systems. At the same time, the increased frequency of "hyperactivity"-like reactions to methylphenidate, as well as higher arterial pressure and lower frequency of defecations seem to reflect an increased excitability of noradrenergic brain systems in rats predisposed to catalepsy.     

Hereditary catalepsy: genetic and molecular mechanisms of catalepsy in mice

The results of experiments on the inheritance and neurobiological mechanism of high predisposition to tonic immobility (catalepsy) in CBA mice are discussed. Genetic analysis has demonstrated a monogenic inheritance of the predisposition to catalepsy. A set of polymorphic microsatellite markers has been used to demonstrate that the predisposition to catalepsy is linked to the distal fragment of mouse chromosome 13, which contains the gene of the 5-HT1A-serotonin receptor. Pharmacological and biochemical evidence for the association between hereditary catalepsy and 5-HT1A-receptor dysfunction are presented. The use of CBA mice for studying the mechanisms of depression and the effects of antidepressants is discussed.     

Distribution of Il6st mRNA and gp130 glycoprotein in various brain structures of mice that differ in intensity of exaggerated freezing reaction (catalepsy)

The glycoprotein gp130 mediates intracellular transduction of signal from receptors of cytokines belonging to the interleukin-6 group. The linkage of the Il6st gene encoding the gp130 protein to heritable predisposition to hypertrophic freezing reaction (catalepsy) has been demonstrated previously in mice. The aim of the present work was to investigate the levels of Il6st mRNA, as well as the distribution of the gp130 protein and the degree of its glycosylation, in five brain regions of mice of the non-cataleptic AKR/J line and the cataleptic lines CBA/LacJ and congenic line AKR.CBA-D13Mit76, which carries the CBA variant of the Il6st gene in the AKR/J genome. These parameters were also studied in mice of the ASC line obtained by backcrossing CBA and AKR mice with the simultaneous selection for the high predisposition to catalepsy. Maximum levels of unglycosylated and glycosylated forms of the gp130 protein were detected in the midbrains of mice from all investigated lines. The highest levels of Il6st mRNA were found in the midbrain, striatum, and hypothalamus of mice of all lines. The level of Il6st mRNA in the striatum of AKR.CBA-D13Mit76 mice was higher than in the striatum of AKR/J mice. Therefore, one can assume that there is a connection between heritable catalepsy and the increased expression of the Il6st gene in the striatum.     

Catalepsy induced by morphine or haloperidol: effects of apomorphine and anticholinergic drugs.

To investigate the extent of cholinergic involvement in opiate-induced catalepsy, the effects of three anticholinergic drugs were studied on morphine-induced catalepsy. Haloperidol-induced catalepsy was also examined. Maximum catalepsy in rats was obtained with 30 mg/kg morphine or 3 mg/kg haloperidol. The anticholinergic drugs atropine, benztropine, and scopolamine were unable to antagonize morphine-induced catalepsy, yet readily antagonized haloperidol-induced catalepsy. Low doses of apomorphine (7.5 mg/kg), on the other hand, readily antagonized morphine catalepsy, but 13-fold higher doses of apomorphine were needed to block haloperidol-induced catalepsy. The results are compatible with the idea that catalepsy can be mediated via the striatum or the amygdala; morphine-dopamine antagonism may occur in the amygdala, whereas morphine-dopamine-cholinergic interactions occur in the striatum.     

Genetic linkage analysis in familial breast and ovarian cancer: results from 214 families. The Breast Cancer Linkage Consortium.

Breast cancer is known to have an inherited component, consistent in some families with autosomal dominant inheritance; in such families the disease often occurs in association with ovarian cancer. Previous genetic linkage studies have established that in some such families disease occurrence is linked to markers on chromosome 17q. This paper reports the results of a collaborative linkage study involving 214 breast cancer families, including 57 breast-ovarian cancer families; this represents almost all the known families with 17q linkage data. Six markers on 17q, spanning approximately 30 cM, were typed in the families. The aims of the study were to define more precisely the localization of the disease gene, the extent of genetic heterogeneity and the characteristics of linked families and to estimate the penetrance of the 17q gene. Under the assumption of no genetic heterogeneity, the strongest linkage evidence was obtained with D17S588 (maximum LOD score [Zmax] = 21.68 at female recombination fraction [theta f] = .13) and D17S579 (Zmax = 13.02 at theta f = .16). Multipoint linkage analysis allowing for genetic heterogeneity provided evidence that the predisposing gene lies between the markers D17S588 and D17S250, an interval whose genetic length is estimated to be 8.3 cM in males and 18.0 cM in females. This position was supported over other intervals by odds of 66:1. The location of the gene with respect to D17S579 could not be determined unequivocally. Under the genetic model used in the analysis, the best estimate of the proportion of linked breast-ovarian cancer families was 1.0 (lower LOD-1 limit 0.79). In contrast, there was significant evidence of genetic heterogeneity among the families without ovarian cancer, with an estimated 45% being linked. These results suggest that a gene(s) on chromosome 17q accounts for the majority of families in which both early-onset breast cancer and ovarian cancer occur but that other genes predisposing to breast cancer exist. By examining the fit of the linkage data to different penetrance functions, the cumulative risk associated with the 17q gene was estimated to be 59% by age 50 years and 82% by age 70 years. The corresponding estimates for the breast-ovary families were 67% and 76%, and those for the families without ovarian cancer were 49% and 90%; these penetrance functions did not differ significantly from one another.