Genes with triplet repeats: candidate mediators of neuropsychiatric disorders

Advancing genomic technologies and clinical awareness accelerates discovery of disease-associated tandem repeat sequences

Expansions of gene-specific DNA tandem repeats (TRs), first described in 1991 as a disease-causing mutation in humans, are now known to cause >60 phenotypes, not just disease, and not only in humans. TRs are a common form of genetic variation with biological consequences, observed, so far, in humans, dogs, plants, oysters, and yeast. Repeat diseases show atypical clinical features, genetic anticipation, and multiple and partially penetrant phenotypes among family members. Discovery of disease-causing repeat expansion loci accelerated through technological advances in DNA sequencing and computational analyses. Between 2019 and 2021, 17 new disease-causing TR expansions were reported, totaling 63 TR loci (>69 diseases), with a likelihood of more discoveries, and in more organisms. Recent and historical lessons reveal that properly assessed clinical presentations, coupled with genetic and biological awareness, can guide discovery of disease-causing unstable TRs. We highlight critical but underrecognized aspects of TR mutations. Repeat motifs may not be present in current reference genomes but will be in forthcoming gapless long-read references. Repeat motif size can be a single nucleotide to kilobases/unit. At a given locus, repeat motif sequence purity can vary with consequence. Pathogenic repeats can be "insertions" within nonpathogenic TRs. Expansions, contractions, and somatic length variations of TRs can have clinical/biological consequences. TR instabilities occur in humans and other organisms. TRs can be epigenetically modified and/or chromosomal fragile sites. We discuss the expanding field of disease-associated TR instabilities, highlighting prospects, clinical and genetic clues, tools, and challenges for further discoveries of disease-causing TR instabilities and understanding their biological and pathological impacts-a vista that is about to expand.

FAN1, a DNA Repair Nuclease, as a Modifier of Repeat Expansion Disorders

FAN1 encodes a DNA repair nuclease. Genetic deficiencies, copy number variants, and single nucleotide variants of FAN1 have been linked to karyomegalic interstitial nephritis, 15q13.3 microdeletion/microduplication syndrome (autism, schizophrenia, and epilepsy), cancer, and most recently repeat expansion diseases. For seven CAG repeat expansion diseases (Huntington's disease (HD) and certain spinocerebellar ataxias), modification of age of onset is linked to variants of specific DNA repair proteins. FAN1 variants are the strongest modifiers. Non-coding disease-delaying FAN1 variants and coding disease-hastening variants (p.R507H and p.R377W) are known, where the former may lead to increased FAN1 levels and the latter have unknown effects upon FAN1 functions. Current thoughts are that ongoing repeat expansions in disease-vulnerable tissues, as individuals age, promote disease onset. Fan1 is required to suppress against high levels of ongoing somatic CAG and CGG repeat expansions in tissues of HD and FMR1 transgenic mice respectively, in addition to participating in DNA interstrand crosslink repair. FAN1 is also a modifier of autism, schizophrenia, and epilepsy. Coupled with the association of these diseases with repeat expansions, this suggests a common mechanism, by which FAN1 modifies repeat diseases. Yet how any of the FAN1 variants modify disease is unknown. Here, we review FAN1 variants, associated clinical effects, protein structure, and the enzyme's attributed functional roles. We highlight how variants may alter its activities in DNA damage response and/or repeat instability. A thorough awareness of the FAN1 gene and FAN1 protein functions will reveal if and how it may be targeted for clinical benefit.

Familial Aggregation in Idiopathic Subglottic Stenosis

OBJECTIVE

To evaluate inheritance patterns and define the familial clustering rate of idiopathic subglottic stenosis (iSGS).

STUDY DESIGN

Retrospective observational study.

SETTING

International multicenter collaborative of >30 tertiary care centers.

METHODS

Patients with a clinically confirmed iSGS diagnosis within the North American Airway Collaborative's iSGS¹⁰⁰⁰ cohort consented between 2014 and 2018 were eligible for enrollment. Patient demographics and disease severity were abstracted from the collaborative's iSGS longitudinal registry. Pedigrees of affected families were created.

RESULTS

A total of 810 patients with iSGS were identified. Positive family history for iSGS was reported in 44 patients in 20 families. The rate of familial clustering in iSGS is 2.5%. Mean age of disease onset is 42.6 years. Of the 44 patients with familial aggregation of iSGS, 42 were female and 2 were male; 13 were mother-daughter pairs and 2 were father-daughter pairs. There were 3 sister-sister pairs. There was 1 niece-aunt pair and 2 groups of 3 family members. One pedigree demonstrated 2 affected mother-daughter pairs, with the mothers being first-degree paternal cousins. Inheritance is non-Mendelian, and anticipation is present in 11 of 13 (84%) parent-offspring pairs. The mean age of onset between parents (48.4 years) and offspring (36.1 years) was significantly different (P = .016).

CONCLUSION

This study quantifies the rate of familial clustering of iSGS at 2.5%. Inheritance is non-Mendelian, and disease demonstrates anticipation. These data suggest that there may be a genetic contribution in iSGS.

Fragile X syndrome. I. An overview on its genetic mechanism

A large body of literature has accumulated within the last decade concerning the fragile X syndrome, the most common cause of X-linked mental retardation. The first article of this review summarizes the peculiar genetic mechanisms and molecular biology properties (eg, unstable DNA triplet repeats), which have been characterized since the detection of the FMR-1 gene in 1991. However, the most important question concerning the function of the FMR-1 gene is still an unresolved issue and is in need of future research. The second article of this review addresses the clinical picture, neuropsychological functioning and psychopathological characteristics of pre- and full mutation carriers.

Incorporation of molecular data and redefinition of phenotype: new approaches to genetic epidemiology of bipolar manic depressive illness and schizophrenia

Considerable advances have been made in identifying specific genetic components of bipolar manic depressive illness (BP) and schizophrenia (SZ), despite their complex inheritance. Meta-analysis of all published whole-genome linkage scans reveals overall support for illness genes in several chromosomal regions. In two of these regions, on the lonq arm of chromosome 13 and on the long arm of chromosome 22, the combined studies of BP and SZ are consistent with a common susceptibility locus for the two disorders. This lends some plausibility to the hypothesis of some shared genetic predispositions for BP and SZ. Other linkages are supported by multiple studies of specific chromosomal regions, most notably two regions on chromosome 6 in SZ. The velocardiofacial syndrome is associated with deletions very close to the linkage region on chromosome 22, and with psychiatric manifestations of both BP and SZ. Endophenotypes of SZ, previously demonstrated to be heritable, have been found to have chromosomal linkage in at least one study. These include eye-tracking abnormalities linked to the short arm of chromosome 6, and abnormality of the P50 cortical evoked potential linked to chromosome 15. Variants in specific genes have been associated with susceptibility to illness, and other genes have been associated with susceptibility to side effects of pharmacological treatment. These genetic findings may eventually be part of an integrated genetic, environmental, and interactive-factor epidemiology of the major mental illnesses.

Mutation analysis of the NRXN1 gene in a Chinese autism cohort

Autism is a brain developmental disorder characterized by impaired social interaction and communication, as well as restricted and repetitive behaviors. The neurexin-1(NRXN1) gene mapped on chromosome 2p16.3 encodes neurexin, a cell adhesion molecule and receptor in the vertebrate nervous system. Rare de novo alterations and copy number variations (CNVs) suggested neurexin-1 as a candidate gene for the pathogenesis of autism, but data on the gene mutation of neurexin-1 in Chinese Han population with autism are limited. By direct sequencing, we analyzed the entire coding regions and associated splice junctions of neurexin-1 in 313 Chinese autism patients. For exons in which non-synonymous variants were identified, sequencing was performed in 500 healthy controls. We identified 22 variants in the neurexin-1 coding regions, including 7 missense variants, 3 deletions, and 12 synonymous mutations. Among them, 3 missense and 3 synonymous variants were not reported in the dbSNP database and absent in 500 control subjects; whereas 4 missense variants, 3 deletions and 3 synonymous mutations were not reported in the dbSNP database but were identified in the control subjects. However, there is no significant association of these mutations with autism risk. Interestingly, there was a statistically significant association of neurexin-1 SNP P300P (rs2303298) with risk of autism (26.2% vs. 13.8%; χ(2) = 22.487; p = 3.45E-006; OR = 2.152 (1.559-2.970)). Our data suggest a possible association of neurexin-1 with autism risk in Chinese Han population, warranting further large-scale study on this gene.

Brain development, infant communication, and empathy disorders: Intrinsic factors in child mental health

Disorders of emotion, communication, and learning in early childhood are considered in light of evidence on human brain growth from embryo stages. We cite microbehavioral evidence indicating that infants are born able to express the internal activity of their brains, including dynamic “motive states” that drive learning. Infant expressions stimulate the development of imitative and reciprocal relations with corresponding dynamic brain states of caregivers. The infant's mind must have an “innate self-with-other representation” of the inter-mind correspondence and reciprocity of feelings that can be generated with an adult.

Primordial motive systems appear in subcortical and limbic systems of the embryo before the cerebral cortex. These are presumed to continue to guide the growth of a child's brain after birth. We propose that an “intrinsic motive formation” is assembled prenatally and is ready at birth to share emotion with caregivers for regulation of the child's cortical development, on which cultural cognition and learning depend.

The intrinsic potentiality for “intersubjectivity” can be disorganized if the epigenetic program for the infant's brain fails. Indeed, many psychological disorders of childhood can be traced to faults in early stages of brain development when core motive systems form.

Time trends in the incidence of type 1 diabetes in Finnish children: a cohort study

BACKGROUND

Finland has the highest incidence of type 1 diabetes worldwide, reaching 40 per 100,000 people per year in the 1990s. Our aim was to assess the temporal trend in type 1 diabetes incidence since 2000 in Finnish children aged younger than 15 years and to predict the number of cases of type 1 diabetes in the future.

METHODS

Children with newly diagnosed type 1 diabetes in Finland who were listed on the National Public Health Institute diabetes register, Central Drug Register, and Hospital Discharge Register in 1980-2005 were included in a cohort study. We excluded patients with type 2 diabetes and diabetes occurring secondary to other conditions, such as steroid use, Down's syndrome, and congenital malformations of pancreas.

FINDINGS

10,737 children-5816 boys and 4921 girls-were diagnosed with type 1 diabetes before 15 years of age during 1980-2005. The average age-standardised incidence was 42.9 per 100,000 per year (95% CI 42.6-44.3) during this period, increasing from 31.4 per 100,000 per year in 1980 to 64.2 per 100,000 per year in 2005. The age-specific rates per 100,000 per year were 31.0, 50.5, and 50.6 at ages 0-4 years, 5-9 years, and 10-14-years, respectively. We noted a significant non-linear component to the time trend (p<0.0003). In children aged 0-4 years, the increase was largest, at 4.7% more affected every year. The overall boy-to-girl ratio of incidence was 1.1; at the age of 13 years, it was 1.7 (1.4-2.0). The predicted cumulative number of new cases with type 1 diabetes before 15 years of age between 2006 and 2020 was about 10 800.

INTERPRETATION

The incidence of type 1 diabetes in Finnish children is increasing even faster than before. The number of new cases diagnosed at or before 14 years of age will double in the next 15 years and the age of onset will be younger (0-4 years).

Childhood autism and associated comorbidities

Autism is a heterogeneous neurodevelopmental disorder with a variety of different etiologies, but with a heritability estimate of more than 90%. Although the strong correlation between autism and genetic factors has been long established, the exact genetic background of autism is still unclear. This review refers to all the genetic syndromes that have been described in children with pervasive developmental disorders (tuberous sclerosis, fragile X, Down, neurofibromatosis, Angelman, Prader-Willi, Gilles de la Tourette, Williams, etc.). Issues covered include prevalence and main characteristics of each syndrome, as well as the possible base of its association with autism in terms of contribution to the current knowledge on the etiology and genetic base of pervasive developmental disorders.

[Fragile X syndrome and very early onset schizophrenia: a female case study]

Genotype-phenotype relationship studies for psychiatric disorders in females carrying fragile X syndrome full mutation and premutation underline association with schizo-affective disorders. In female children with X fragile full mutation, only behavioural symptoms and no standardised psychiatric disorders have been systematically explored. Therefore, we report the case of a nine-year-old girl carrying the fragile X syndrome full mutation with a comorbid childhood onset schizophrenia (COS), and of her mother carrying the fragile X syndrome premutation and a comorbid schizotypal personality disorder. The impact of these associations is discussed regarding the recent literature in chromosome anomalies in COS.

Differential expression of Huntington's disease gene (IT15) mRNA in developing rat brain

Huntington's disease (HD) is an autosomal dominant inheritance neurological disorder associated with CAG repeats expansions within a widely distributed gene that causes selective neuronal death. The gene is essential for normal development and has been suggested for its role in the development of basal ganglia. To understand its normal function during growth and development, we determined the expression patterns for the gene responsible for HD (IT15) mRNA by Northern blot analysis in the developing and adult rat brain. In adult rat brains, IT15 transcripts exist as two isoforms of 10 and 12.5 kb each, which display distinct expression patterns. IT15 mRNA expression is already highly expressed within 1 day of birth. Expression signals for IT15 were first detected at embryonic day 16 or 17 during prenatal development. IT15 transcript peaks leveled around day 20 postnatally and thereafter decreased to levels typically found in adults. In the adult rat brain, mRNA expression was highest in the cerebellum followed by the cortex, striatum, hippocampus and olfactory lobe. In the medulla and the spinal cord, IT15 was weakly expressed in comparison to the other regions studied. Thus, the distinct expression patterns provide a basis for its functional significance during development. These results also suggest that the degree of IT15 mRNA expression is related to the neuronal population in different brain regions.

Novel CAG/CTG repeat expansion mutations do not contribute to the genetic risk for most cases of bipolar disorder or schizophrenia

The possible presence of anticipation in bipolar affective disorder and schizophrenia has led to the hypothesis that repeat expansion mutations could contribute to the genetic etiology of these diseases. Using the repeat expansion detection (RED) assay, we have systematically examined genomic DNA from 100 unrelated probands with schizophrenia and 68 unrelated probands with bipolar affective disorder for the presence of CAG/CTG repeat expansions. Our results show that 28% of the probands with schizophrenia and 30% of probands with bipolar disorder have a CAG/CTG repeat in the expanded range, but that each expansion could be explained by one of three nonpathogenic repeat expansions known to exist in the general population. We conclude that novel CAG/CTG repeat expansions are not a common genetic risk factor for bipolar disorder or schizophrenia.

Molecular understanding of aluminum-induced topological changes in (CCG)12 triplet repeats: relevance to neurological disorders

Recent studies have shown that gene mutations are involved in the pathology of neurological disorders. CCG repeats cause genetic instability and are localized at the 5' end of the non-coding regions of the FMR1 gene in fragile X syndrome. Our studies for the first time showed that aluminum (Al) levels were elevated in the serum samples of fragile X syndrome and also provide evidence for the interaction of aluminum with (CCG)12-repeats. Circular dichroism spectroscopic studies of (CCG)12 indicated B-DNA conformation and in the presence of Al (10(-5) M) CCG repeats attained Z-DNA conformation. Further spectroscopic studies, which included melting profiles, ethidium bromide binding patterns and interaction of Z-DNA specific polyclonal antibodies confirmed the Z-conformation in (CCG)12-repeats in the presence of Al (10(-5) M). It is interesting to mention that Al-induced Z-conformation is stable even after the total removal of Al from CCG by desferoximine, a chelating drug. This is the first report to proof the role of Al in modulating the DNA (CCG repeats) topology and this information provides a clue about the possible involvement of Al at a molecular level in neurological/neurodegenerative disorders.

Simple sequences are rare in the Protein Data Bank

A simple sequence is abundant in the proteins that have been sequenced to date. But unusual protein features, such as a simple sequence, are not present in the same high frequency within structural databases. A subset of these simple sequences, a group with a highly repetitive nature has been shown to be abundant in eukaryotes but not in prokaryotes. In this study, an examination of the eukaryotic proteins in the Protein Data Bank (PDB) has revealed a large deficiency of low complexity, highly repetitive protein repeats. Through simulated databases of similar samples of eukaryotic proteins taken from the National Center for Biotechnology Information (NCBI) database, it is shown that the PDB contains a significantly less highly repetitive, simple sequence than artificial databases of similar composition randomly derived from NCBI. When the structural data for those few PDB sequences that did contain a highly repetitive simple sequence is examined in detail, it is found that in most cases the tertiary structure is unknown for the regions consisting of a simple sequence. This lack of a simple sequence both in the PDB database and in the structural information suggests that this type of simple sequence may produce disordered structures that make structural characterization difficult.

Molecular genetics of schizophrenia: past, present and future

Schizophrenia is a severe neuropsychiatric disorder with a polygenic mode of inheritance which is also governed by non-genetic factors. Candidate genes identified on the basis of biochemical and pharmacological evidence are being tested for linkage and association studies. Neurotransmitters, especially dopamine and serotonin have been widely implicated in its etiology. Genome scan of all human chromosomes with closely spaced polymorphic markers is being used for linkage studies. The completion and availability of the first draft of Human Genome Sequence has provided a treasure-trove that can be utilized to gain insight into the so far inaccessible regions of the human genome. Significant technological advances for identification of single nucleo-tide polymorphisms (SNPs) and use of microarrays have further strengthened research methodologies for genetic analysis of complex traits. In this review, we summarize the evolution of schizophrenia genetics from the past to the present, current trends and future direction of research.

Progress toward discovery of susceptibility genes for bipolar manic-depressive illness and schizophrenia

The inconsistency in linkage results that has bedeviled psychiatric genetics has been observed to occur regularly in common diseases with complex inheritance. Nonetheless, in two such instances--noninsulin-dependent diabetes mellitus (NIDDM) and inflammatory bowel disease (IBD)--susceptibility genes have been discovered based on the follow-ups of linkage findings. In bipolar illness disorder (BPD) and schizophrenia (SZ), there are some linkage reports with replication of other studies similar to the situation in NIDDM and IBD before the successful positional cloning efforts. Two of the regions with linkage reports, BPD and SZ, on the long arms of chromosomes 13 and 22, show linkage to the same markers in both diseases. This lends some plausibility to the hypothesis of some shared genetic predispositions for both disorders. Cytogenetic evidence offers another positional approach to susceptibility genes. The velocardiofacial syndrome is associated with deletions very close to the linkage region on chromosome 22, and with psychiatric manifestations of both BPD and SZ. Endophenotypes of SZ, previously demonstrated to the be heritable, have been found to have chromosomal linkage in at least one study. These include eye-tracking abnormalities linked to 6p, and an abnormality of the P50 cortical evoked potential linked to chromosome 15. Variants in specific genes have been associated with susceptibility to the psychiatric illnesses. These genetic findings may contribute to etiologic subcategorization of BPD and SZ, and the development of new treatment approaches. A table of genetic terms is included for review

Imprinted genes and mental dysfunction

There is a rapidly accumulating body of evidence from family, adoption and twin studies suggestive of a genetic component to many common mental disorders. In some cases, the transmission of abnormalities has been shown to be dependent upon the sex of the parent from whom they are inherited. Such 'parent-of-origin effects' may be explained by a number of genetic mechanisms, one of which is 'genomic imprinting'. In imprinted genes one allele is silenced according to its parental origin. This in turn means that imprinted traits are passed down the maternal or paternal line, in contrast to the more frequent Mendelian mode of inheritance that is indifferent to the parental origin of the allele. In the present review, we survey the evidence for the influence of imprinted genes on a number of mental disorders, ranging from explicit imprinted conditions, where in some cases abnormalities have been mapped to particular gene candidates, to examples where the evidence for parent-of-origin effects is less strong. We also consider, briefly, the wider implications of imprinted effects on mental dysfunction, in particular with respect to evolutionary pressures on mammalian brain development and function.

Anticipation in bipolar affective disorder: is age at onset a valid criterion?

Anticipation has been suggested among the genetic mechanisms of bipolar disorder (BD), prompting the search for unstable DNA sequences. Past studies of anticipation in BD have generally relied on observed shift in the age at onset between parental and offspring generations. Such a shift, however, may be caused by a number of other factors difficult to correct for. We investigated age at onset distributions in a sample of 161 related subjects and in a sample of "pseudofamilies" consisting of 320 unrelated subjects selected from a large epidemiological cohort using Monte-Carlo simulation to mimic the family sample. Comparison of age at onset distributions in both samples shows a difference between the generations, but of a similar magnitude in each sample. This suggests that age at onset alone may not be a sufficient criterion of anticipation. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:804-807, 2000.

No evidence for a parent-of-origin effect detected in the pattern of inheritance of schizophrenia

BACKGROUND

Schizophrenia is a complex genetic disorder with no clear pattern of inheritance. Epigenetic modification of genes may thus play a role in its transmission.

METHODS

In our study, 439 families with at least two ill siblings with schizophrenia (208 with unilineal transmission) were examined for evidence of a parent-of-origin effect (e.g., evidence of parental imprinting on the familial transmission of schizophrenia).

RESULTS

No significant difference in the prevalence of maternal compared with paternal transmission was found. In addition, affected male subjects did not differ from affected female subjects in the proportion of their offspring diagnosed with schizophrenia.

CONCLUSIONS

Although the transmission of schizophrenia may be influenced by epigenetic events, our study fails to find evidence that one epigenetic mechanism, a parent-of-origin imprinting effect, determines whether an individual expresses the illness.

pMGA phenotypic variation in Mycoplasma gallisepticum occurs in vivo and is mediated by trinucleotide repeat length variation

Chickens were infected with a pathogenic strain of Mycoplasma gallisepticum, and the expression of pMGA, the major surface protein, was inferred by examination of colonies from ex vivo cells. Within 2 days postinfection, 40% of cells had ceased the expression of the original pMGA surface protein (pMGA1.1), and by day 6, the majority of recovered cells were in this category. The switch in pMGA phenotype which had occurred in vivo was reversible, since most colonies produced from ex vivo progenitors exhibited frequent pMGA1. 1(+) sectors. After prolonged in vivo habitation, increasing proportions of recovered cells gave rise to variant pMGA colonies which had switched from the expression of pMGA1.1 to another gene, pMGA1.2, concomitant with the acquisition of a (GAA)(12) motif 5' to its promoter. Collectively, the results suggest that changes in M. gallisepticum pMGA gene expression in vivo are normal, common, and possibly obligate events for successful colonization of the host. Surprisingly, the initial cessation of pMGA1.1 expression occurred in the absence of detectable pMGA antibodies and seemed to precede the adaptive immune response.

A CAG trinucleotide repeat expansion and familial schizophrenia

Studies which showed anticipation in families with schizophrenia suggested that a trinucleotide repeat expansion mechanism may be involved in the pathogenesis of familial schizophrenia. Furthermore, some studies involving the repeat expansion detection (RED) method showed the median length of CAG repeats to be longer in probands with schizophrenia than that in control subjects. We screened for a possible expanded CAG repeat by means of the direct identification of repeat expansion and cloning technique in 23 subjects (affected, 14; unaffected, 9) from six families with schizophrenia which showed anticipation. The polymorphism of a long and unstable CAG/CTG trinucleotide repeat, Dir1, was studied by PCR. No unusual expanded CAG/CTG trinucleotide repeat was detected in the subjects with familial schizophrenia. There was no significant difference between the affected and unaffected subjects in the allele frequency of Dir1. Our results suggest that a CAG expansion is not the mechanism underlying familial schizophrenia.

Clinical characteristics of bipolar disorder subjects with large CAG/CTG repeat DNA

BACKGROUND

Unstable DNA has been implicated in a variety of neuropsychiatric disorders, with increasing severity of disease associated with larger DNA repeats. We examined the unstable DNA hypothesis for bipolar disorder by looking for increased severity of symptoms and earlier age of onset amongst bipolar individuals with large CAG/CTG repeats.

METHODS

From a sample of 91 bipolar subjects, eight with large CAG/CTG (> or = 270bp) trinucleotide repeats were matched to eight bipolar individuals with small repeats (< or = 150bp). Medical charts were reviewed for age of onset and a number of severity indicators. Candidate CAG/CTG expansions on chromosomes 17 and 18 were also genotyped.

RESULTS

No obvious differences were noted for the clinical indices, however seven out of eight individuals with large Repeat Expansion Detection (RED) products had expansions at the CTG18.1 locus, while four out of eight had large repeats at ERDA1. Both of these sites are unlikely to be related to disease.

LIMITATIONS

Our total sample size is small and less than 9% have large repeats.

CONCLUSIONS

The lack of increased severity or earlier age of onset amongst bipolar subjects with large CAG/CTG repeats suggests these repeats are unlikely to have a major etiological role in bipolar disorder.

Properties of polyglutamine expansion in vitro and in a cellular model for Huntington's disease

Eight neurodegenerative diseases have been shown to be caused by the expansion of a polyglutamine stretch in specific target proteins that lead to a gain in toxic property. Most of these diseases have some features in common. A pathological threshold of 35-40 glutamine residues is observed in five of the diseases. The mutated proteins (or a polyglutamine-containing subfragment) form ubiquitinated aggregates in neurons of patients or mouse models, in most cases within the nucleus. We summarize the properties of a monoclonal antibody that recognizes specifically, in a Western blot, polyglutamine stretches longer than 35 glutamine residues with an affinity that increases with polyglutamine length. This indicates that the pathological threshold observed in five diseases corresponds to a conformational change creating a pathological epitope, most probably involved in the aggregation property of the carrier protein. We also show that a fragment of a normal protein carrying 38 glutamine residues is able to aggregate into regular fibrils in vitro. Finally, we present a cellular model in which the induced expression of a mutated full-length huntingtin protein leads to the formation of nuclear inclusions that share many characteristics with those observed in patients: those inclusions are ubiquitinated and contain only an N-terminal fragment of huntingtin. This model should thus be useful in studying a processing step that is likely to be important in the pathogenicity of mutated huntingtin.

Synthesis of 2'beta-Deoxy-[8-(13)C;amino,9-(15)N(2)]adenosine: Unusual Annulation Conditions To Assemble the Purine Core

Synthesis of 2'beta-Deoxy-[8-(13)C;amino,9-(15)N(2)]adenosine has been accomplished using a five-step process which employs a novel annulation of [(13)C]formamide [N-(4-[(15)N]amino-6-chloro-5-pyrimidinyl)] 2. To effect this dehydration, a complex of triethyl phosphite and TiCl(2)(i-OPr)(2) was used. 6-Chloro-[8-(13)C; 9-(15)N]purine was then converted in two steps to 2'beta-deoxy-[8-(13)C;amino,9-(15)N(2)]adenosine.

Progressive catatonia

We present the case of a young man with a diagnosis of a childhood-onset pervasive developmental disorder who developed a progressive neurologic deterioration with persistent catatonia and right hemiparesis. On his initial evaluation approximately three years after the onset of mutism, he manifested right hemiparesis and catalepsy. Two years later, although catalepsy had subsided, motor function had deteriorated so that he could not use his hands to feed or dress himself. Oral-facialbuccal dyskinesia manifested by blepharospasm and grimacing were present constantly during waking hours. Quantitative electroencephalography demonstrated markedly decreased amplitude, a finding associated with catatonia. Left sural nerve biopsy indicated large axon cylinder degeneration. Left deltoid biopsy demonstrated perimysial fibrosis and type II fiber predominance. Although magnetic resonance imaging of the head without contrast was normal, positron emission tomography indicated hypometabolism of the right cerebral and the right cerebellar hemispheres. The patient continues to deteriorate despite a course of 25 electroconvulsive treatments. He continues to manifest criteria for catatonia including motoric immobility, mutism, and peculiarities of voluntary movement such as prominent grimacing. We suspect an inherited neurodegenerative disorder. Since catatonia is a treatable condition frequently associated with medical and neurological diseases, examination for the features of catatonia must be included in the assessment of patients with progressive brain degeneration. This report is an attempt to clarify the traits of a serious variant of progressive brain degeneration.

Triplet repeat variability in the signal peptide sequence of the Xmrk receptor tyrosine kinase gene in Xiphophorus fish

Trinucleotide repeats in several human genes have been found to undergo spontaneous variation in repeat numbers in succeeding generations. Expansion of the repeat beyond a certain length causes specific pathological disorders. So far, a naturally occurring triplet repeat instability of transcribed sequences has been reported only from humans. However, the signal peptide encoding region of the receptor tyrosine kinase gene Xmrk from fish of the genus Xiphophorus contains a CTG repeat that differs in length even between closely related individuals. The consequence of this variability is signal peptides with shorter or longer hydrophobic core regions reaching, in some individuals, the critical maximum length for functional protein export or even exceeding it. In one stock, animals that are homozygous for such an allele were extremely rare, indicating that the triplet repeat length variability of the Xmrk gene of Xiphophorus may indeed have an influence on the function of the gene product and, under certain conditions, may affect the fitness of the individual.

Expression of the pMGA genes of Mycoplasma gallisepticum is controlled by variation in the GAA trinucleotide repeat lengths within the 5' noncoding regions

We analyzed the segment of DNA which contains the expressed pMGA gene from one strain of Mycoplasma gallisepticum in normal (strain S6) cells and in cells in which pMGA1.1 gene expression had ceased as a consequence of in vitro culture in the presence of pMGA1. 1-specific antibodies. Sequence analysis of isolates lacking pMGA1.1 expression revealed that this gene, which is typically expressed, exhibited sequence changes within a region 5' to its promoter. Specifically, pMGA1.1(+) cells contained a (GAA)12 motif upstream of the promoter, whereas in pMGA1.1(-) cells the corresponding region contained a (GAA)10 motif; when such cells were grown in medium no longer containing pMGA-specific antibodies, pMGA1.1 was reexpressed and the 5' (GAA)12 motif was restored. Two other genes, pMGA1.9 and pMGA1.2, were also shown to acquire a (GAA)12 motif in clones which expressed these genes. The results imply the evolution by the pMGA genes of M. gallisepticum of a novel transcriptional requirement which facilitates rapid and reversible switches in the pMGA expression pattern.

Atrophin-1, the DRPLA gene product, interacts with two families of WW domain-containing proteins

Atrophin-1 contains a polyglutamine repeat, expansion of which is responsible for dentatorubral and pallidoluysian atrophy (DRPLA). The normal function of atrophin-1 is unknown. We have identified five atrophin-1 interacting proteins (AIPs) which bind to atrophin-1 in the vicinity of the polyglutamine tract using the yeast two-hybrid system. Four of the interactions were confirmed using in vitro binding assays. All five interactors contained multiple WW domains. Two are novel. The AIPs can be divided into two distinct classes. AIP1 and AIP3/WWP3 are MAGUK-like multidomain proteins containing a number of protein-protein interaction modules, namely a guanylate kinase-like region, two WW domains, and multiple PDZ domains. AIP2/WWP2, AIP4, and AIP5/WWP1 are highly homologous, each having four WW domains and a HECT domain characteristic of ubiquitin ligases. These interactors are similar to recently isolated huntingtin-interacting proteins, suggesting possible commonality of function between two proteins responsible for very similar diseases.

Polymorphisms of the glucocorticoid receptor gene in laboratory and wild rats: steroid binding properties of trinucleotide CAG repeat length variants

The polyglutamine tract, beginning at codon 75 in the N-terminal modulatory domain of rat glucocorticoid receptor (rGR), was analyzed in 61 inbred strains and 155 wild caught Rattus norvegicus. A discontinuous distribution of repeat lengths was found (7, 17-23 repeats). To investigate the possible significance of this distribution, full-length rGR cDNAs with 7, 18, 20, and 21 CAG repeats were expressed in CV-1 cells, and the resulting GR protein analyzed by Western blots and extensive Scatchard analyses. The quantity and steroid binding capacity of GR, together with the binding affinities for dexamethasone and corticosterone, were found to be indistinguishable for the four repeat alleles. From the sequencing of four inbred strains CAG repeat variants were found to be flanked by silent allelic substitutions at nucleotide positions 198, 531, and 711. The four variable sites extended over 471-519 bp of coding sequence, forming six Grl haplotypes. The results are discussed in the light of genetic studies on the Milan hypertensive and normotensive strains of rat. Codon sequence of rat GR required amendment at the following residues: D98, G226, D260, P600, and F602.

Solution structures of the Huntington's disease DNA triplets, (CAG)n

Highly polymorphic DNA triplet repeats, (CAG)n, are located inside the first exon of the Huntington's disease gene. Inordinate expansion of this repeat is correlated with the onset and progression of the disease. NMR spectroscopy, gel electrophoresis, digestion by single-strand specific P1 enzyme, and in vitro replication assay have been used to investigate the structural basis of (CAG)n expansion. Nondenaturing gel electrophoresis and 1D 1H NMR studies of (CAG)5 and (CAG)6 reveal the presence of hairpins and mismatched duplexes as the major and minor populations respectively. However, at high DNA concentrations (i.e., 1.0-2.0 mM that is typically required for 2D NMR experiments) both (CAG)5 and (CAG)6 exist predominantly in mismatched duplex forms. Mismatched duplex structures of (CAG)5 and (CAG)6 are useful, because they adequately model the stem of the biologically relevant hairpins formed by (CAG)n. We, therefore, performed detailed NMR spectroscopic studies on the duplexes of (CAG)5 and (CAG)6. We also studied a model duplex, (CGCAGCG)2 that contains the underlined building block of the duplex. This duplex shows the following structural characteristics: (i) all the nucleotides are in (C2'-endo, anti) conformations, (ii) mismatched A x A base pairs are flanked by two Watson-Crick G x C base pairs and (iii) A x A base pairs are stably stacked (and intra-helical) and are formed by a single N6-H--N1 hydrogen bond. The nature of A x A pairing is confirmed by temperature-dependent HMQC and HMQC-NOESY experiments on the [(CA*G)5]2 duplex where the adenines are 15N-labeled at N6. Temperature- and pH-dependent imino proton spectra, nondenaturing electrophoresis, and P1 digestion data demonstrate that under a wide range of solution conditions longer (CAG)n repeats (n> or =10) exist exclusively in hairpin conformation with two single-stranded loops. Finally, an in vitro replication assay with (CAG)8,21 inserts in the M13 single-stranded DNA templates shows a replication bypass for the (CAG)21 insert but not for the (CAG)8 insert in the template. This demonstrates that for a sufficiently long insert (n=21 in this case), a hairpin is formed by the (CAG)n even in presence of its complementary strand. This observation implies that the formation of hairpin by the (CAG)n may cause slippage during replication and thus may explain the observed length polymorphism.

Molecular cloning and characterization of a human brain-specific gene implicated in neuronal differentiation

A 2.5 kb human cDNA clone containing a CAG trinucleotide repeat, designated HB20, was isolated from a human fetal brain library. Northern analysis on multi-tissue blots and various cell lines confirmed that HB20 is specifically expressed in the brain. Its expression is low in two glioma cells, moderate in a neuron precursor cell, NT2, but absent in lymphoma, cervical carcinoma, or colonic carcinoma cells. Significant increase of HB20 mRNA was shown along with retinoic acid-induced terminal differentiation of NT2 cells into neuron cells, hNT. Homology comparison of the predicted HB20 amino acid sequence with the current database revealed that it belongs to a newly recognized protein family composed of nucleosome assembly proteins and SET proto-oncogene, which has been shown to interact specifically with B-type cyclins involved in the control of cell proliferation. Together with the detection of nuclear localization signals and apparent nuclear distribution of expressed protein, HB20 is likely to be a brain-specific nuclear protein, functioning in the process of neuronal differentiation.

Anticipation and imprinting in schizophrenia

Anticipation, i.e., a decrease in the age of onset and/or an increase in the severity of a disease in subsequent generations, and imprinting, i.e., different modes of parental transmission, have been suggested in trinucleotide repeat amplification diseases. The purpose of this study was to determine if anticipation and imprinting are associated with familial schizophrenia. Two generations of 49 schizophrenics from 24 families were studied. Ages of onset, numbers hospitalized, diagnostic subclasses of schizophrenia, amounts of antipsychotics, positive symptoms, negative symptoms, treatment resistance, and clinical course ratings, were compared between the two generations. The age of onset was significantly lower in the offspring generation, although there was no difference in the severity between the two generations. The negative symptom scores and clinical course scores in the offspring generation for paternal transmission were significantly higher than those for maternal transmission. Our results suggest the presence of imprinting and anticipation in schizophrenia.

Exclusion of five trinucleotide repeat (CAG and CCG) expansions in 17 families with schizophrenia

Trinucleotide repeat expansion diseases are characterized by anticipation. Several studies suggested the anticipation in schizophrenia. We studied five novel trinucleotide repeats identified by Li et al in a human brain cDNA library in 100 unrelated control subjects, and 57 subjects in 17 families with schizophrenia. The CTG-B43 and B45d, and CCG-A3 were not polymorphic in any unrelated control subjects or subjects with familial schizophrenia. The CTG-A4 had two alleles and the CTG-B1 three alleles. The two clones were not expanded in subjects with familial schizophrenia or unrelated healthy controls. There was no difference in allele frequency between unrelated control subjects and subjects in the families with schizophrenia. The allele frequencies in unaffected and affected subjects in the families with schizophrenia were not significantly different. There was no difference between the offspring and parental generations of affected subjects in the families with schizophrenia. The results suggest the exclusion of the five trinucleotide repeat expansions in the 17 families with schizophrenia.

A novel, heritable, expanding CTG repeat in an intron of the SEF2-1 gene on chromosome 18q21.1

There are currently 13 diseases known to be caused by unstable triplet repeat mutations; however, there are some instances (as with FRAXF and FRA16) when these mutations appear to be asymptomatic. In a search for polymorphic CTG repeats as candidate genes for bipolar disorder, we screened a genomic human chromosome 18-specific library and identified a 1.6 kb clone (7,6A) with a CTG24 repeat that maps to 18q21.1. The CTG repeat locus, termed CTG18.1, is located within an intron of human SEF2-1, a gene encoding a basic hellx-loop-hellx DNA binding protein involved in transcriptional regulation. The CTGn repeat is highly polymorphic and very enlarged alleles, consistent with expansions of up to CTG2100, were identified. PCR and Southern blot analysis in pedigrees ascertained for a Johns Hopkins University bipolar disorder linkage study and in CEPH reference pedigrees revealed a tripartite distribution of CTG18.1 alleles with stable alleles (CTG10-CTG37), moderately enlarged and unstable alleles (CTG53-CTG250), and very enlarged, unstable alleles (CTG800-CTG2100). Moderately enlarged alleles were not associated with an abnormal phenotype and have a combined enlarged allele frequency of 3% in the CEPH and bipolar populations. Very enlarged alleles, detectable only by Southern blot analysis of genomic digests, have thus far been found in only three individuals from our bipolar pedigrees, and to date, have not been found in any of the CEPH reference pedigrees. These enlarged alleles may arise, at least in part, via somatic mutation.

Identification and chromosomal localization of human genes containing CAG/CTG repeats expressed in testis and brain

Human genes containing triplet repeats have been demonstrated to be involved in several neurodegenerative diseases by expansion of the repeat in succeeding generations. To identify novel genes involved in such pathologies, we have isolated transcripts containing (CAG/CTG)n repeats using two approaches. First, we screened 4 x 10(6) clones representing 10 copies of a human testis cDNA library using a (CAG)14 oligonucleotide probe. Among the 910 clones identified, the 243 clones with the strongest hybridization signal were sequenced partially from 3' or 5' ends. This provided us with 251 partial sequences that grouped into clusters corresponding to 39 genes, of which 19 represent unknown species. Second, we selected 203 additional ESTs containing (CAG/CTG)n repeats representing 121 clusters from the IMAGE consortium infant brain cDNA library. From these two series of sequences, we have localized 95 genes on human chromosomes using a panel of whole genome radiation hybrid (Genebridge 4). These genes are located on all of the chromosomes except for chromosome X, the highest density being observed on chromosome 19.

Molecular mechanism of regulation of pentylenetetrazol-induced calcium entry by 3'-untranslated region of a seizure-related cDNA, PTZ-17, in Xenopus oocytes

To determine the molecular mechanism of regulation of pentylenetetrazol (PTZ)-induced calcium entry by the seizure-related gene, PTZ-17, the role of the 3'-untranslated region (3'UTR) and also interaction between 3'UTR and intracellular factors were investigated. PTZ-induced calcium inward current in Xenopus oocytes injected with PTZ-17 RNA varied in magnitude among strains of mice: RNA derived from the DBA/2 mouse, which has a high susceptibility to convulsions, showed the largest current and that from the BALB/c mouse with a low susceptibility to convulsions showed no PTZ response. The sequence of 3'UTR showed alterations among mouse strains: 3'UTR of BALB/c showed a sequence alteration from T to G and that of DBA/2 showed a GTG insertion compared with that of B6. The 3'UTR also regulated the translation of chloramphenicol acetyltransferase (CAT) RNA depending on its sequence. A particular region within the 3'UTR demonstrated interaction with 60- and 47-kDa proteins. Sequence alterations in this region corresponded to disappearance or increase in PTZ-induced calcium entry. These findings suggest that a particular region within 3'UTR of the seizure-related gene, PTZ-17, is involved in PTZ-induced calcium entry via interaction between mRNA and specific RNA-binding proteins.

Dentatorubral and pallidoluysian atrophy (DRPLA). Clinical and neuropathological findings in genetically confirmed North American and European pedigrees

Dentatorubral and pallidoluysian atrophy (DRPLA) is an autosomal dominant disorder that clinically overlaps with Huntington's disease (HD) and manifests combinations of chorea, myoclonus, seizures, ataxia, and dementia. DRPLA is caused by a CAG triplet repeat (CTG-B37) expansion coding for polyglutamine on chromosome 12 and exhibits the genetic phenomenon of anticipation. This neurodegenerative disease has only rarely been reported in non-Japanese pedigrees, and there are only a few neuropathological studies in genetically confirmed patients. We report 10 cases of DRPLA from two North American and two British pedigrees in which CTG-B37 expansions have been demonstrated within each kindred (54-83 repeats), individually in 8 of the 10 cases, and describe the neuropathological findings in 4 cases. Members of DRPLA kindreds have a wide range of clinical phenotypes and markedly variable ages at onset. The neuropathological spectrum is centered around the cerebellifugal and pallidofugal systems, but neurodegenerative changes can be found in many nuclei, tracts, and systems. Evidence of CTG-B37 triplet repeat expansion should be sought in HD-like cases that are negative for expanded triplet repeats within the HD IT15 gene or in autopsy cases with degeneration of the dentatorubral or pallidoluysian systems.

Anticipation in schizophrenia: biology or bias?

Anticipation is a genetic phenomenon wherein age of disease onset decreases and/ or severity increases in successive generations. Anticipation has been demonstrated for several neuropsychiatric disorders with expanding trinucleotide repeats recently identified as the underlying molecular mechanism. We report here the results of an analysis of anticipation performed with multiplex families segregating schizophrenia. Thirty-three families were identified through the NIMH Genetics Initiative that met the following criteria: had at least two affected members in successive generations and were not bilineal. Affectation diagnoses included schizophrenia, schizoaffective disorder-depressed, and psychosis NOS. Additional analyses included the Cluster A personality disorders. Three indices of age of onset were used. Disease severity was measured by several different indices. Four sampling schemes as suggested by McInnis et al. were tested, as well as additional analysis using pairs ascertained through the parental generation. Anticipation was demonstrated for age of onset, regardless of the index or sampling scheme used (P<0.05). Anticipation was not supported for disease severity. Analyses that took into account drug use and diminished fecundity did not affect the results. While the data strongly support intergenerational differences in disease onset consistent with anticipation, they must be viewed cautiously given unavoidable biases attending these analyses.

Analysis of the CAG repeats in the SCA1 and B37 genes in schizophrenic and bipolar I disorder patients: tentative association between B37 and schizophrenia

We have genotyped unrelated French Alsatian schizophrenic and bipolar I disorder (BPD) patients and matched controls for the polymorphic CAG repeats within the genes for spinocerebellar ataxia type 1 (SCA1) and dentatorubral-pallidoluysian atrophy (B37), in order to test their possible involvement in these disorders. No alleles with abnormally expanded repeats were found in either gene in patients and controls. Differences in allele and genotype frequencies for the SCA1 CAG repeat between patients and controls were not significant, thus providing no support for its role as a possible positional candidate gene for schizophrenia and BPD in our patients. Chi square testing revealed a significant result (P = 0.019) for an association between the B37 CAG repeat on chromosome 12p and schizophrenia. This result was more significant when only schizophrenics with a positive family history were compared with controls (P = 0.0001). The frequencies of alleles with 14, 12, and 15 CAG repeats differed the most, respectively, between schizophrenics and controls. When choosing the median of the B37 allele distribution (15 CAG repeats) as a threshold, there were significantly more controls than schizophrenics in the group with longer alleles (15 or more repeats) and more schizophrenics with shorter alleles (P = 0.002 by Fisher exact test). No particular genotype was associated with schizophrenia. This result possibly indicates linkage disequilibrium with another locus on chromosome 12p and therefore deserves further attention. No association was found between the B37 CAG repeat and patients with BPD.

Genomic survey of bipolar illness in the NIMH genetics initiative pedigrees: a preliminary report

Four sites collaborated with the NIMH to develop a resource for the genetic study of bipolar (BP) illness. Common methods of ascertainment and assessment were developed in 1989. A series of families with a bipolar I (BPI) proband and at least one BPI or schizoaffective, bipolar type (SA/BP) first-degree relative has been studied. We now report initial data from a genomic survey with an average intermarker interval of 10 cM on 540 subjects from 97 families. This is the largest commonly ascertained and assessed linkage sample for bipolar illness reported to date; it includes 232 subjects with BPI, 32 SA/BP, 72 bipolar II (BPII), and 88 unipolar, recurrent (UPR). Nonparametric methods of analysis were employed, with all sites using affected sib pair analysis. The strongest findings thus far appear to be on chromosomes 1, 6, 7, 10, 16, and 22. Support has also been found for some previously reported linkages, including 21q and possibly Xq26. All these areas (as well as others) will be followed up with additional markers and further analyses. No locus tested thus far meets stringent criteria for an initial finding of significant linkage.

Meiotic instability associated with the CAGR1 trinucleotide repeat at 13q13

CAGR1 is a recently characterised polymorphic trinucleotide repeat localised to 13q13, which has been suggested as a possible candidate gene for neurological disorders that manifest genetic anticipation. To provide evidence in support of this hypothesis, a large number of chromosomes (n = 928) from patients with a wide variety of neurological diseases were screened for evidence of repeat expansion and meiotic instability. One person with a CAGR1 repeat number of 50 was identified (normal range 9-29). Subsequent molecular analyses of CAGR1 repeat number in additional family members showed meiotic instability of a (CAG)45 allele through three generations. While CAGR1 repeat number did not correlate with a readily discernible phenotype in this family, the finding of meiotic stability and mendelian inheritance of normal CAG alleles and meiotic instability of larger repeats fulfil several criteria thought essential for pathologically relevant mutations of this type. Thus, these data strengthen the hypothesis for a role of CAGR1 in the development of an as yet molecularly uncharacterised human neurological disease.

Differential display of genome subsets containing specific interspersed repeats

A genomic differential display method was developed that analyzes many restriction fragment length polymorphisms simultaneously. Interspersed repeat sequences were used to reduce DNA sample complexity and to target genomic subsets of interest. This work focused on trinucleotide repeats because of their importance in human inherited diseases. Immobilized repeat-containing oligonucleotides were used to capture genomic DNA fragments containing sequences complementary to the oligonucleotide. Captured fragments were amplified by PCR and fluorescently labeled using primers complementary to the repeat sequence and/or to the known sequences ligated to the ends of the restriction fragments. The labeled PCR fragments were displayed by size on a high-resolution automated fluorescent DNA sequencing instrument. Although there was a conservation in the overall pattern of displayed genome subsets, many clear and reproducible differences were detected when genomes from different individuals were compared. Fewer differences were detected within, than between, monozygotic twin pair genomes. In control experiments, the method distinguished between Huntington disease alleles with normal and expanded CAG repeat lengths.

Carbonic anhydrase II and carbonic anhydrase-related protein in the cerebellar cortex of normal and lurcher mice

The developmental profiles of carbonic anhydrase II (CA-II) and a carbonic anhydrase related protein (CARP) were studied in rat and mouse cerebella. Enzyme histochemistry, immunohistochemistry, in situ hybridisation and Western blotting were used to study the synthesis and expression of these enzymes in cerebellar sections from age matched control, CA-II deficient and lurcher mice, the latter being characterised by Purkinje cell degeneration. Both CA-II and CARP were first found to be expressed in the Purkinje cells in the 9 day old mouse, and the immunoreactivity of both peptides increased with time. Immunohistochemistry showed more intense staining of CARP than of CA-II in Purkinje cells throughout the developmental profile of the mouse, and this was mirrored by the mRNA levels determined by in situ hybridisation. Immunohistochemistry of CA-II and CARP also demonstrated the progressive dendritic growth of the mouse and rat Purkinje cells. CA-II and CARP immunoreactivity ceased by the end of cerebellar maturation. The onset of Purkinje cell degeneration was detected at day 10 in the lurcher mouse, with concomitant marked decrease in CA-II level: however CARP expression was found to be unchanged. By postnatal day 16 neither CA-II mRNA, protein, nor activity was detectable in contrast to CARP which remained at a decreased level unit the Purkinje cells population had completely degenerated. Our findings suggest a role of CA-II in the degenerative processes of the lurcher Purkinje cells, with CARP playing an important role in the development and maturation of the cerebellar cortex.

A novel membrane glycoprotein, SHPS-1, that binds the SH2-domain-containing protein tyrosine phosphatase SHP-2 in response to mitogens and cell adhesion

Protein tyrosine phosphatases (PTPases), such as SHP-1 and SHP-2, that contain Src homology 2 (SH2) domains play important roles in growth factor and cytokine signal transduction pathways. A protein of approximately 115 to 120 kDa that interacts with SHP-1 and SHP-2 was purified from v-src-transformed rat fibroblasts (SR-3Y1 cells), and the corresponding cDNA was cloned. The predicted amino acid sequence of the encoded protein, termed SHPS-1 (SHP substrate 1), suggests that it is a glycosylated receptor-like protein with three immunoglobulin-like domains in its extracellular region and four YXX(L/V/I) motifs, potential tyrosine phosphorylation and SH2-domain binding sites, in its cytoplasmic region. Various mitogens, including serum, insulin, and lysophosphatidic acid, or cell adhesion induced tyrosine phosphorylation of SHPS-1 and its subsequent association with SHP-2 in cultured cells. Thus, SHPS-1 may be a direct substrate for both tyrosine kinases, such as the insulin receptor kinase or Src, and a specific docking protein for SH2-domain-containing PTPases. In addition, we suggest that SHPS-1 may be a potential substrate for SHP-2 and may function in both growth factor- and cell adhesion-induced cell signaling.