Clinical Value of Imaging Using Antibody to Alpha Fetoprotein in Germ Cell Tumours

Germ cell tumours (GCT) producing alpha fetoprotein (aFP) can be imaged by external scintigraphy after intravenous administration of radiolabelled antibody directed against aFP. Antibody imaging (AI) by this method was used in an attempt to guide surgical resection of deposits of drug-resistant or recurrent GCT. 30 patients with GCT and raised aFP in whom site of tumour was not known were investigated by AI and conventional imaging methods. All but one were heavily pretreated. Where tumour appeared localised, resection was attempted. Tumour was found in all sites positive by both AI and conventional imaging. AI produced false-positive results in one of 30 patients and falsenegative results in 9 patients. Computerised tomography was false-positive in one case and false-negative in three. In these patients, AI gave true-negative and true-positive results, respectively. Of 11 patients with positive AI in whom resection was attempted, 6 achieved sustained complete response with up to 5 years follow-up. We conclude AI and conventional imaging methods to be complementary in selection for surgery of patients with drug-resistant or recurrent GCT.

An ordered sequence of expression of human MHC class-II antigens during B-cell maturation?

Studies with monoclonal antibodies confirm that human MHC class-II antigens are encoded by at least three pairs of loci. Here Keith Guy and Veronica van Heyningen suggest that as B cells mature theproducts of these loci are expressed in the sequence SB → DR → DC antigens - a sequence which parallels the order of the genes on chromosome 6.

FISH mapping of de novo apparently balanced chromosome rearrangements identifies characteristics associated with phenotypic abnormality

We report fluorescence in situ hybridization (FISH) mapping of 152, mostly de novo, apparently balanced chromosomal rearrangement (ABCR) breakpoints in 76 individuals, 30 of whom had no obvious phenotypic abnormality (control group) and 46 of whom had an associated disease (case group). The aim of this study was to identify breakpoint characteristics that could discriminate between these groups and which might be of predictive value in de novo ABCR (DN-ABCR) cases detected antenatally. We found no difference in the proportion of breakpoints that interrupted a gene, although in three cases, direct interruption or deletion of known autosomal-dominant or X-linked recessive Mendelian disease genes was diagnostic. The only significant predictor of phenotypic abnormality in the group as a whole was the localization of one or both breakpoints to an R-positive (G-negative) band with estimated predictive values of 0.69 (95% CL 0.54-0.81) and 0.90 (95% CL 0.60-0.98), respectively. R-positive bands are known to contain more genes and have a higher guanine-cytosine (GC) content than do G-positive (R-negative) bands; however, whether a gene was interrupted by the breakpoint or the GC content in the 200 kB around the breakpoint had no discriminant ability. Our results suggest that the large-scale genomic context of the breakpoint has prognostic utility and that the pathological mechanism of mapping to an R-band cannot be accounted for by direct gene inactivation.

Developmental malformations of the eye: the role of PAX6, SOX2 and OTX2

Eye development initiates as an evagination of the early neural plate, before the closure of the neural tube. Structural malformations of the eye such as anophthalmia and microphthalmia arise very early in development. It is not surprising therefore that three of the genes currently identified to play a significant role in these developmental eye anomalies are also major players in brain development and regionalization. However, as has been emerging for a high proportion of transcriptional regulators studied, these genes have evolved to play multiple roles throughout development, and perhaps even in adult tissue maintenance. This complex spatiotemporal expression pattern requires elaborate regulatory systems which we are beginning to unravel. A major component of these complex regulatory networks is a series of cis-acting elements, highly conserved through evolution, which spread large distances from the coding region of each gene. We describe how cross regulation for PAX6, SOX2 and perhaps OTX2 has now been uncovered, pointing to the mechanisms that can fine-tune the expression of such essential developmental components. These interactions also help us understand why there is significant phenotypic overlap between mutations at these three loci.

Cognitive functioning in humans with mutations of thePAX6gene

Fourteen patients with PAX6 gene mutations and previously identified MRI abnormalities were administered tests of cognitive functioning. No deficits were found. A subgroup with agenesis of the anterior commissure performed significantly more poorly on measures of working memory than those without this abnormality, suggesting the anterior commissure may play a role in cognitive processing in addition to an earlier identified role in sensory development and processing.

National study of microphthalmia, anophthalmia, and coloboma (MAC) in Scotland: investigation of genetic aetiology

We report an epidemiological and genetic study attempting complete ascertainment of subjects with microphthalmia, anophthalmia, and coloboma (MAC) born in Scotland during a 16 year period beginning on 1 January 1981. A total of 198 cases were confirmed giving a minimum live birth prevalence of 19 per 100 000. One hundred and twenty-two MAC cases (61.6%) from 115 different families were clinically examined and detailed pregnancy, medical, and family histories obtained. A simple, rational, and apparently robust classification of the eye phenotype was developed based on the presence or absence of a defect in closure of the optic (choroidal) fissure. A total of 85/122 (69.7%) of cases had optic fissure closure defects (OFCD), 12/122 (9.8%) had non-OFCD, and 25/122 (20.5%) had defects that were unclassifiable owing to the severity of the corneal or anterior chamber abnormality. Segregation analysis assuming single and multiple incomplete ascertainment, respectively, returned a sib recurrence risk of 6% and 10% in the whole group and 8.1% and 13.3% in the OFCD subgroup. Significant recurrence risks were found in both unilateral and bilateral disease. In four families, one parent had an OFCD, two of which were new diagnoses in asymptomatic subjects. All recurrences in first degree relatives occurred in the OFCD group with a single first cousin recurrence seen in the non-OFCD group. A total of 84/122 of the MAC cases were screened for mutations in the coding regions of PAX6, CHX10, and SIX3. No pathogenic mutations were identified in the OFCD cases. A single PAX6 homeodomain missense mutation was identified in a subject with partial aniridia that had been initially misclassified as coloboma.

Aniridia-associated translocations, DNase hypersensitivity, sequence comparison and transgenic analysis redefine the functional domain of PAX6

The transcription factor PAX6 plays a critical, evolutionarily conserved role in eye, brain and olfactory development. Homozygous loss of PAX6 function affects all expressing tissues and is neonatally lethal; heterozygous null mutations cause aniridia in humans and the Small eye (Sey) phenotype in mice. Several upstream and intragenic PAX6 control elements have been defined, generally through transgenesis. However, aniridia cases with chromosomal rearrangements far downstream of an intact PAX6 gene suggested a requirement for additional cis-acting control for correct gene expression. The likely location of such elements is pinpointed through YAC transgenic studies. A 420 kb yeast artificial chromosome (YAC) clone, extending well beyond the most distant patient breakpoint, was previously shown to rescue homozygous Small eye lethality and correct the heterozygous eye phenotype. We now show that a 310 kb YAC clone, terminating just 5' of the breakpoint, fails to influence the Sey phenotypes. Using evolutionary sequence comparison, DNaseI hypersensitivity analysis and transgenic reporter studies, we have identified a region, >150 kb distal to the major PAX6 promoter P1, containing regulatory elements. Components of this downstream regulatory region drive reporter expression in distinct partial PAX6 patterns, indicating that the functional PAX6 gene domain extends far beyond the transcription unit.

PAX6 mutation in a family with aniridia, congenital ptosis, and mental retardation

Congenital aniridia is due to deletions and point mutations in the PAX6 gene. We describe here a case of a mother and her two sons with a syndrome comprising congenital aniridia, ptosis, and slight mental retardation. The sons also show behavioral changes. The possibility of deletion around the PAX6 locus was excluded by polymorphism studies and fluorescence in situ hybridization analysis. Mutation screening of the PAX6 gene revealed the presence of a transversion C719A, resulting in the substitution of arginine for serine at residue 119. We suggest that this missense mutation is responsible both for aniridia and ptosis, and possibly also for the observed cognitive dysfunction in this family.

PAX6 haploinsufficiency causes cerebral malformation and olfactory dysfunction in humans

PAX6 is widely expressed in the central nervous system. Heterozygous PAX6 mutations in human aniridia cause defects that would seem to be confined to the eye. Magnetic resonance imaging (MRI) and smell testing reveal the absence or hypoplasia of the anterior commissure and reduced olfaction in a large proportion of aniridia cases, which shows that PAX6 haploinsuffiency causes more widespread human neuro developmental anomalies.

Hemolytic uremic syndrome associated with Denys-Drash syndrome

The Denys-Drash syndrome is defined by the occurrence of combinations of pseudohermaphroditism, nephrotic syndrome with diffuse mesangial sclerosis, Wilms' tumor, and constitutional mutations in the WT1 suppressor gene. Most patients develop end-stage renal failure. Atypical hemolytic uremic syndrome (HUS) is defined by onset of acute hemolytic anemia with fragmented erythrocytes, thrombocytopenia, and renal failure in the absence of a gastrointestinal prodromal illness of bloody diarrhea. The purpose of this report is to describe the occurrence of features of atypical HUS and Denys-Drash syndrome in two African-American boys aged 13 and 16 months. Each had nephrotic syndrome, diffuse mesangial sclerosis, and WT1 point mutations. Both had grade III hypospadias and undescended testes. They had normal serum creatinine concentrations and hematology a month before presenting with HUS. Stool cultures for Escherichia coli O157:H7 were negative. Each patient has been transplanted with cadaver kidneys without recurrence of HUS.

Phenotypic variability and asymmetry of Rieger syndrome associated with PITX2 mutations

PURPOSE

Rieger syndrome is an autosomal dominant condition characterized by a variable combination of anterior segment dysgenesis, dental anomalies, and umbilical hernia. To date, reports have shown mutations within the PITX2 gene associated with Rieger syndrome, iridogoniodysgenesis, and iris hypoplasia. The purposes of this study were to determine the range of expression and intrafamilial variability of PITX2 mutations in patients with anterior segment dysgenesis.

METHODS

Seventy-six patients with different forms of anterior segment dysgenesis were classified clinically. DNA was obtained and screened by means of polymerase chain reaction (PCR)-single-stranded conformation polymorphism (SSCP) and heteroduplex analysis followed by direct sequencing.

RESULTS

Eight of 76 patients had mutations within the PITX2 gene. Anterior segment phenotypes show wide variability and include a phenocopy of aniridia and Peters', Rieger, and Axenfeld anomalies. Mutations include premature terminations and splice-site and homeobox mutations, confirming that haploinsufficiency the likely pathogenic mechanism in the majority of cases.

CONCLUSIONS

There is significant phenotypic variability in patients with PITX2 mutations, both within and between families. Developmental glaucoma is common. The umbilical and dental abnormalities are highly penetrant, define those at risk of carrying mutations in this gene, and guide mutation analysis. In addition, there is a range of other extraocular manifestations.

PAX6 mutations reviewed

Mutations in PAX6 are responsible for human aniridia and have also been found in patients with Peter's anomaly, with congenital cataracts, with autosomal dominant keratitis, and with isolated foveal hypoplasia. No locus other than chromosome 11p13 has been implicated in aniridia, and PAX6 is clearly the major, if not only, gene responsible. Twenty-eight percent of identified PAX6 mutations are C-T changes at CpG dinucleotides, 20% are splicing errors, and more than 30% are deletion or insertion events. There is a noticeably elevated level of mutation in the paired domain compared with the rest of the gene. Increased mutation in the homeodomain is accounted for by the hypermutable CpG dinucleotide in codon 240. Very nearly all mutations appear to cause loss of function of the mutant allele, and more than 80% of exonic substitutions result in nonsense codons. In a gene with such extraordinarily high sequence conservation throughout evolution, there are presumed undiscovered missense mutations, these are hypothesized to exist in as-yet unidentified phenotypes.

A new set of primers for mutation analysis of the human PAX6 gene

Mutations in the human PAX6 gene are an important cause of dominantly inherited congenital malformations of the eye, including aniridia, Peters' anomaly, keratitis, and isolated foveal hypoplasia. To satisfy the need for efficient detection of PAX6 mutations, we have developed a new set of oligonucleotides for genomic SSCP based on the recently completed genomic sequence of the entire human PAX6 gene. We also describe PAX6 mutations in eight aniridia patients, five of which are novel.

Role of Pax6 in development of the cerebellar system

Post-mitotic neurons generated at the rhombic lip undertake long distance migration to widely dispersed destinations, giving rise to cerebellar granule cells and the precerebellar nuclei. Here we show that Pax6, a key regulator in CNS and eye development, is strongly expressed in rhombic lip and in cells migrating away from it. Development of some structures derived from these cells is severely affected in Pax6-null Small eye (Pax6(Sey)/Pax6(Sey)) embryos. Cell proliferation and initial differentiation seem unaffected, but cell migration and neurite extension are disrupted in mutant embryos. Three of the five precerebellar nuclei fail to form correctly. In the cerebellum the pre-migratory granule cell sub-layer and fissures are absent. Some granule cells are found in ectopic positions in the inferior colliculus which may result from the complete absence of Unc5h3 expression in Pax6(Sey)/Pax6(Sey) granule cells. Our results suggest that Pax6 plays a strong role during hindbrain migration processes and at least part of its activity is mediated through regulation of the netrin receptor Unc5h3.

Psychiatric disorder and cognitive function in a family with an inherited novel mutation of the developmental control gene PAX6

The PAX family of developmental control genes are known to play important roles in the early patterning of the central nervous system. One member of this family, PAX6, is involved in eye development in invertebrates as well as in mouse and man, but is also widely expressed in the developing forebrain. Humans with a mutation in this gene have abnormalities of eye development, and the results presented here suggest, for the first time, that this mutation may also be associated with subtle abnormalities of frontal lobe function in the family studied. We carried out genotyping of individuals within a single family, with and without the characteristic eye abnormalities of PAX6 mutation, and only those individuals with the mutation showed significant abnormalities on tests of frontal lobe function. These individuals also had higher rates of psychiatric disorder. PAX6 is highly conserved between mouse and man, and although the neuroanatomical phenotype associated with PAX6 heterozygosity has only been studied in mice, the resultant cellular disorganization seen in mice is likely to be present in the human forebrain. Although these mice have no obvious behavioural phenotype, the results presented here suggest that humans with the equivalent mutation display a neurobehavioural phenotype.

Multiple roles for the Wilms' tumor suppressor, WT1

Wilms' tumor is a childhood kidney tumor that is a striking example of the way that cancer may arise through development gone awry. A proportion of these tumors develop as a result of the loss of function mutations in the Wilms' tumor suppressor gene, WT1. Inherited mutations in the WT1 gene can lead to childhood kidney cancer, severe gonadal dysplasia, and life-threatening hypertension. Knockouts show that the gene is essential for the early stages of kidney and gonad formation. These tissues are completely absent in null mice. The WT1 gene encodes numerous protein isoforms, all of which share four zinc fingers. There is a large body of evidence supporting the notion that WT1 is a transcription factor, particularly a transcriptional repressor. Recently, however, we obtained evidence that WT1 colocalizes and is physically associated with splice factors. What is more, one alternative splice isoform of WT1 containing three amino acids, Lys-Thr-Ser (KTS; inserted between zinc fingers 3 and 4) is preferentially associated with splice factors, whereas the other alternative splice version, lacking these three amino acids, preferentially associates with the transcriptional apparatus. Both genetic and evolutionary considerations suggest that these two different forms of the protein have different functions. We will discuss recent evidence to further implicate WT1 in splicing. Our results raise the possibility that regulation of splicing is a crucial factor in the development of the genitourinary system, and that tumors may arise through aberrant splicing. To pursue the regulation and function of WT1 in whole animals, we have been introducing the human gene and large flanking regions cloned in yeast artificial chromosomes directly into mice. These studies have allowed us to dissect the function of WT1 at late as well as at early stages in organogenesis and to identify new sites and surprising new potential functions for the gene.

Missense mutations in the most ancient residues of the PAX6 paired domain underlie a spectrum of human congenital eye malformations

Mutations of the human PAX6 gene underlie aniridia (congenital absence of the iris), a rare dominant malformation of the eye. The spectrum of PAX6 mutations in aniridia patients is highly biased, with 92% of all reported mutations leading to premature truncation of the protein (nonsense, splicing, insertions and deletions) and just 2% leading to substitution of one amino acid by another (missense). The extraordinary conservation of the PAX6 protein at the amino acid level amongst vertebrates predicts that pathological missense mutations should in fact be common even though they are hardly ever seen in aniridia patients. This indicates that there is a heavy ascertainment bias in the selection of patients for PAX6 mutation analysis and that the 'missing' PAX6 missense mutations frequently may underlie phenotypes distinct from textbook aniridia. Here we present four novel PAX6 missense mutations, two in association with atypical phenotypes: ectopia pupillae (displaced pupils) and congenital nystagmus (searching gaze), and two in association with more recognizable aniridia phenotypes. Strikingly, all four mutations are located within the PAX6 paired domain and affect amino acids which are highly conserved in all known paired domain proteins. Our results support the hypothesis that the under-representation of missense mutations is caused by ascertainment bias and suggest that a substantial burden of PAX6 -related disease remains to be uncovered.

EYA4, a novel vertebrate gene related to Drosophila eyes absent

We have isolated a family of four vertebrate genes homologous to eyes absent (eya), a key regulator of ocular development in Drosophila. Here we present the detailed characterization of the EYA4 gene in human and mouse. EYA4 encodes a 640 amino acid protein containing a highly conserved C-terminal domain of 271 amino acids which in Drosophila eya is known to mediate developmentally important protein-protein interactions. Human EYA4 maps to 6q23 and mouse Eya4 maps to the predicted homology region near the centromere of chromosome 10. In the developing mouse embryo, Eya4 is expressed primarily in the craniofacial mesenchyme, the dermamyotome and the limb. On the basis of map position and expression pattern, EYA4 is a candidate for oculo-dento-digital (ODD) syndrome, but no EYA4 mutations were found in a panel of ODD patients.

Complete sequencing of the Fugu WAGR region from WT1 to PAX6: dramatic compaction and conservation of synteny with human chromosome 11p13

The pufferfish Fugu rubripes has a genome approximately 7.5 times smaller than that of mammals but with a similar number of genes. Although conserved synteny has been demonstrated between pufferfish and mammals across some regions of the genome, there is some controversy as to what extent Fugu will be a useful model for the human genome, e.g., [Gilley, J., Armes, N. & Fried, M. (1997) Nature (London) 385, 305-306]. We report extensive conservation of synteny between a 1.5-Mb region of human chromosome 11 and <100 kb of the Fugu genome in three overlapping cosmids. Our findings support the idea that the majority of DNA in the region of human chromosome 11p13 is intergenic. Comparative analysis of three unrelated genes with quite different roles, WT1, RCN1, and PAX6, has revealed differences in their structural evolution. Whereas the human WT1 gene can generate 16 protein isoforms via a combination of alternative splicing, RNA editing, and alternative start site usage, our data predict that Fugu WT1 is capable of generating only two isoforms. This raises the question of the extent to which the evolution of WT1 isoforms is related to the evolution of the mammalian genitourinary system. In addition, this region of the Fugu genome shows a much greater overall compaction than usual but with significant noncoding homology observed at the PAX6 locus, implying that comparative genomics has identified regulatory elements associated with this gene.

Position effect in human genetic disease

The spatially, temporally and quantitatively correct expression of a gene requires the presence not only of intact coding sequence, free of adverse nucleotide changes, but also correctly functioning regulatory control. With the identification of an increasing number of disease-related genes, the molecular defect in many cases has been defined. It is becoming clear that it is not always the transcription unit that bears the defect: there are a number of cases where the regulation of gene expression has been compromised. Cases associated with chromosomal rearrangement outside the transcription and promoter regions are categorized as position effects. A number of different mechanisms may explain their aetiology. Here, we examine the human disorders where such position effects are implicated. Further study of such cases may lead to important insights into mechanisms of gene regulation and transcriptional control.

In utero nephropathy, Denys-Drash syndrome and Potter phenotype

We report an unusual case of Denys-Drash syndrome presenting in a newborn infant with end-stage renal failure of antenatal origin and Potter phenotype. DNA analysis showed a novel missense change in arginine 394 of zinc finger 3 of the WT1 gene. This mutation may lead to an earlier and more severe presentation of Denys-Drash syndrome. It may be of interest to look for this mutation in other Potter phenotype cases.

The Human PAX6 Mutation Database

The Human PAX6 Mutation Database contains details of 94 mutations of the PAX6 gene. A Microsoft Access program is used by the Curator to store, update and search the database entries. Mutations can be entered directly by the Curator, or imported from submissions made via the World Wide Web. The PAX6 Mutation Database web page at URL http://www.hgu.mrc.ac.uk/Softdata/PAX6/ provides information about PAX6, as well as a fill-in form through which new mutations can be submitted to the Curator. A search facility allows remote users to query the database. A plain text format file of the data can be downloaded via the World Wide Web. The Curation program contains prior knowledge of the genetic code and of the PAX6 gene including cDNA sequence, location of intron/exon boundaries, and protein domains, so that the minimum of information need be provided by the submitter or Curator.

Tandem duplication of 11p12-p13 in a child with borderline development delay and eye abnormalities: dose effect of the PAX6 gene product?

We report on a girl with a duplication of chromosome band 11p12-->13, which includes the Wilms tumor gene (WT1) and the aniridia gene (PAX6). The girl had borderline developmental delay, mild facial anomalies, and eye abnormalities. Eye findings were also present in most of the 11 other published cases with partial trisomy 11p, including 11p12-->13. Recently, it was shown that introduction of additional copies of the PAX6 gene into mice caused very variable eye abnormalities. Therefore, a PAX6 gene dosage effect is likely to be present in mice and humans. The central nervous system may be less sensitive to an altered PAX6 gene dosage, which is consistent with the borderline developmental delay in the present patient. Urogenital abnormalities were absent in this patient and in most of the other patients with partial trisomy of 11p. Therefore, the effect of a WT1 gene duplication on the embryological development of the urogenital tract remains uncertain.

Combined SSCP/heteroduplex analysis in the screening for PAX6 mutations

We demonstrate the use of combined SSCP and heteroduplex analysis in the detection of PAX6 mutations using non-radioactive silver staining. A panel of aniridia patients was screened by this approach and we show that a greater number of mutations was detected than would have been found by running each technique alone. Six previously unreported aniridia mutations in PAX6 are also described..

Pax6 controls progenitor cell identity and neuronal fate in response to graded Shh signaling

Distinct classes of motor neurons and ventral interneurons are generated by the graded signaling activity of Sonic hedgehog (Shh). Shh controls neuronal fate by establishing different progenitor cell populations in the ventral neural tube that are defined by the expression of Pax6 and Nkx2.2. Pax6 establishes distinct ventral progenitor cell populations and controls the identity of motor neurons and ventral interneurons, mediating graded Shh signaling in the ventral spinal cord and hindbrain.

The reticulocalbin gene maps to the WAGR region in human and to the Small eye Harwell deletion in mouse

We describe the localization of the gene encoding reticulocalbin, a Ca2+-binding protein of the endoplasmic reticulum, on human chromosome 11p13 midway between the WT1 and the PAX6 genes and show that it is hemizygously deleted in WAGR individuals. The mouse reticulocalbin gene is also shown to map to the region of conserved synteny on mouse chromosome 2 and to be deleted in the Small eye Harwell (SeyH) mutation. Loss of the reticulocalbin gene could contribute to the early lethality of SeyH and SeyDey homozygotes.

The incidence of PAX6 mutation in patients with simple aniridia: an evaluation of mutation detection in 12 cases

Twelve aniridia patients, five with a family history and seven presumed to be sporadic, were exhaustively screened in order to test what proportion of people with aniridia, uncomplicated by associated anomalies, carry mutations in the human PAX6 gene. Mutations were detected in 90% of the cases. Three mutation detection techniques were used to determine if one method was superior for this gene. The protein truncation test (PTT) was used on RT-PCR products, SSCP on genomic PCR amplifications, and chemical cleavage of mismatch on both RT-PCR and genomic amplifications. For RT-PCR products, only the translated portion of the gene was screened. On genomic products exons 1 to 13 (including 740 bp of the 3' untranslated sequence and all intron/exon boundaries) were screened, as was a neuroretina specific enhancer in intron 4. Ten of the possible 12 mutations in the five familial cases and five of the sporadic patients were found, all of which conformed to a functional outcome of haploinsufficiency. Five were splice site mutations (one in the donor site of intron 4, two in the donor site of intron 6, one in each of the acceptor sites of introns 8 and 9) and five were nonsense mutations in exons 8, 9, 10, 11, and 12. SSCP analysis of individually amplified exons, with which nine of the 10 mutations were seen, was the most useful detection method for PAX6.

A FISH approach to defining the extent and possible clinical significance of deletions at the WAGR locus

Nineteen patients were analysed by fluorescence in situ hybridisation (FISH) with selected 11p13 markers. They were examined because they had either isolated sporadic or familial aniridia, or aniridia with one or more of the WAGR (Wilms' tumour, aniridia, genital anomalies, and mental retardation) syndrome anomalies. The FISH markers from distal 11p13 were cosmids FO2121, PAX6 (aniridia), D11S324, and WT1 (Wilms' tumour predisposition). Two of the patients with isolated aniridia were abnormal, one with an apparently balanced reciprocal 7;11 translocation and an 11p13 breakpoint, which by FISH was shown to be approximately 30 kb distal to the aniridia (PAX6) gene, and the other had a submicroscopic deletion involving part of PAX6 that extended distally for approximately 245 kb. Two patients with aniridia together with other WAGR malformations had deletions involving all four cosmids. One case with aniridia associated with developmental and growth delay had a deletion including FO2121 and PAX6 but not D11S324 and WT1, while in a further case the deletion included all four test cosmids. These studies show that a combined conventional and molecular cytogenetic approach to patients presenting with aniridia is a useful method for differentiating between those with deletions extending into and including WT1 and therefore between those with high and low risks of developing Wilms' tumour.

Influence of PAX6 gene dosage on development: overexpression causes severe eye abnormalities

Aniridia in man and Small eye in mice are semidominant developmental disorders caused by mutations within the paired box gene PAX6. Whereas heterozygotes suffer from iris hypoplasia, homozygous mice lack eyes and nasal cavities and exhibit brain abnormalities. To investigate the role of gene dosage in more detail, we have generated yeast artificial chromosome transgenic mice carrying the human PAX6 locus. When crossed onto the Small eye background, the transgene rescues the mutant phenotype. Strikingly, mice carrying multiple copies on a wild-type background show specific developmental abnormalities of the eye, but not of other tissues expressing the gene. Thus, at least five different eye phenotypes are associated with changes in PAX6 expression. We provide evidence that not only reduced, but also increased levels of transcriptional regulators can cause developmental defects.

EagI and NotI linking clones from human chromosomes 11 and Xp

EagI and NotI linking libraries were prepared in the lambda vector, EMBL5, from the mouse-human somatic cell hybrid 1W1LA4.9, which contains human chromosomes 11 and Xp as the only human component. Individual clones containing human DNA were isolated by their ability to hybridise with total human DNA and digested with SalI and EcoRI to identify the human insert size and single-copy fragments. The mean (+/- SD) insert sizes of the EagI and NotI clones were 18.3 +/- 3.2 kb and 16.6 +/- 3.6 kb, respectively. Regional localisation of 66 clones (52 EagI, 14 NotI) was achieved using a panel of 20 somatic cell hybrids that contained different overlapping deletions of chromosomes 11 or Xp. Thirty-nine clones (36 EagI, 3 NotI) were localised to chromosome 11; 17 of these were clustered in 11q13 and another nine were clustered in 11q14-q23.1. Twenty-seven clones (16 EagI, 11 NotI) were localised to Xp and 10 of these were clustered in Xp11. The 66 clones were assessed for seven different microsatellite repetitive sequences; restriction fragment length polymorphisms for five clones from 11q13 were also identified. These EagI and NotI clones, which supplement those previously mapped to chromosome 11 and Xp, should facilitate the generation of more detailed maps and the identification of genes that are associated with CpG-rich islands.

Transcription factors in disease

Mutations affecting several predominantly tissue-specific transcriptional regulators have recently been associated with disease phenotypes. Although the mutational spectrum is variable, many of the reported cases involve clear loss-of-function mutations-such as Waardenburg syndrome type 1, aniridia and Rubinstein-Taybi syndrome-suggesting that the genetic mechanism involved in disease is haplo-insufficiency. The high degree of dosage sensitivity often appears to affect only a subset of the tissues that express the gene. Position effects with cytogenetic rearrangements well outside the coding region have been implicated for four of the genes discussed: POU3F4, SOX9, PAX6, and GL13.

The evolution of WT1 sequence and expression pattern in the vertebrates

WT1 is a Wilms' tumour predisposition gene, encoding a protein with four C-terminal Kruppel-type zinc fingers, which is also a major regulator of kidney and gonadal development. To pinpoint key regulatory domains involved in development and evolution of the vertebrate genitourinary system, we have isolated WT1 orthologues from all gnathostome classes. Partial nucleotide sequence from chick, alligator, Xenopus laevis and zebrafish reveals extensive conservation. Both the zinc fingers and the transregulatory domain exhibit a high level of similarity in all the species examined. However, of the two alternatively spliced regions only one, the three amino acid KTS insertion between zinc fingers 3 and 4, is found in species other than mammals. The 17 amino acid insertion at the C-terminal end of the transregulatory domain is present only in mammals. Residues with reported human pathological mutations are also unaltered across species, underlining their structural significance. Studies in chick and alligator reveal that the mammalian intermediate mesoderm expression pattern is conserved in birds and reptiles. A wider role in mesodermal differentiation is suggested by expression in some paraxial and lateral mesoderm derivatives.

Micronucleus frequencies in lymphoblastoid cell lines measured with the cytokinesis-block technique and flow cytometry

In these experiments, the cytokinesis-block technique was used to measure the spontaneous and radiation-induced micronucleus frequencies in lymphoblastoid cell lines from normal individuals and individuals with radiation-sensitive syndromes. The radiation-induced micronucleus frequencies were measured at different harvest times to investigate the optimum time to measure radiation-induced cytogenetic damage with the cytokinesis-block technique. The frequency of radiation-induced micronuclei was found to be independent of the frequency of binucleate cells in these cell lines. Longer incubation times were complicated by increasing numbers of mononucleate and multinucleate cells, and scoring slides at an early incubation time after the maximum frequency of binucleate cells is reached was recommended. Two of the cell lines (one established from an individual with ataxia telangiectasia, and one from an infant with mitotic instability) had significantly higher radiation-induced micronucleus frequencies than the control cell lines. Finally, the radiation-induced micronucleus frequencies in three of the cell lines were measured by flow cytometry, and the results ranked the cell lines in the same order of radiosensitivity as the cytokinesis block technique.

A new PAX6 mutation in familial aniridia

Aniridia (lack of iris) is caused by loss of function mutations in one copy of the PAX6 gene. Here we present a new PAX6 splice mutation in a family with autosomal dominant aniridia. The mutation is a single nucleotide change which, although occurring within an exon, affects the splice junction consensus and results in skipping of that exon.

Subnuclear localization of WT1 in splicing or transcription factor domains is regulated by alternative splicing

WT1 is a tumor suppressor gene with a key role in urogenital development and the pathogenesis of Wilms' tumor. Two alternative splice sites in the WT1 transcript allow the gene to encode four proteins. These carry four Krüppel-type zinc fingers and to date have primarily been implicated in transcriptional control of genes involved in growth regulation. However, here we demonstrate colocalization of WT1 with splicing factors in the fetal kidney and testis and in expressing cell lines. Using immunoprecipitation, we show that two WT1 isoforms directly associate with one or a limited number of components in the spliceosomes and coiled bodies. Moreover, COS cell expression studies suggest that alternative splicing within the WT1 zinc finger region determines whether the protein localizes mainly with splicing factors or with DNA in transcription factor domains in the nucleus. We propose that WT1 plays roles in posttranscriptional processing of RNA as well as in transcription.

DNA binding capacity of the WT1 protein is abolished by Denys-Drash syndrome WT1 point mutations

Constitutional point mutations in the zinc finger (ZF) region of the Wilms' tumour suppressor gene 1 (WT1) lead to Denys-Drash syndrome (DDS). Patients with this syndrome display renal failure, Wilms' tumour (WT) and pseudohermaphroditism. DDS WT1 mutations fall into three major categories: (a) missense mutations altering amino acids which directly interact with the DNA target; (b) substitution of amino acids involved in zinc complexing; and (c) nonsense mutations leading to the removal of at least two zinc fingers. We have expressed the WT1 zinc fingers as glutathione-S-transferase fusion proteins, with the lysine-threonine-serine (KTS) alternate splice between ZF3 and ZF4 either present or absent. WT1 fusion constructs with all three classes of DDS mutation were also created. Wild-type and mutant fusion proteins were assayed for their DNA-binding affinity using four previously identified WT1 DNA targets: an EGR1 consensus site; murine insulin-like growth factor 2 promoter 2 (IGF2P2); a (TCC)n motif from the PDGFA-chain promoter; and +P5, a genomic fragment isolated by its affinity for WT1 + KTS. WT1-KTS bound all four targets, but WT1 + KTS only bound +P5. All three classes of DDS mutation investigated, with or without KTS, abolished binding to all four targets. This provides evidence that DDS mutations act either as dominant-negative antimorphs, or elicit their effect through disturbed isoform dosage balance.

Does the Wilms' tumour suppressor gene, WT1, play roles in both splicing and transcription?

The Wilms' tumour suppressor gene (WT1) encodes a protein(s) with 4 zinc fingers that is essential for the development of the genitourinary system. A considerable body of evidence exists to support the idea that WT1 binds DNA and functions as a transcription factor. However, we have shown recently by confocal microscopy and immunoprecipitation studies that a significant proportion of WT1 is associated with splice factors in kidney cell lines, fetal tissues and transfected Cos cells. Different isoforms of WT1 are produced by an alternative splice that leads to the presence or absence of a 3 amino acid insertion (KTS) between zinc fingers 3 and 4. We have shown that these different forms localise differently in the nucleus. The +KTS form mainly localises with splice factors, the -KTS form mainly with transcription factors. Here we propose a model to account for these different localisations. Also, we discuss the possible significance of these findings.

Placement and refined mapping of established and new markers on human chromosome 11q using a small panel of somatic cell hybrids

Constructing detailed chromosome maps relies on the ability to place new markers rapidly and accurately. Here we map two new anonymous DNA markers precisely on chromosome 11q and refine the location of established markers using a panel of just six fragmentation hybrids, with reference to four translocation chromosomes. As several of the hybrids retain multiple segments of chromosome 11, it is possible to quickly assign new markers to subintervals using this modest set of hybrid DNAs.

Assignment of 112 microsatellite markers to 23 chromosome 11 subregions delineated by somatic hybrids: comparison with the genetic map

Using a panel of 25 somatic cell hybrids, we have regionally localized 112 microsatellite markers generated by Généthon and assigned to chromosome 11. A genetic map of 74 of them was produced using linkage analysis of the eight largest CEPH (Centre d'Etude du Polymorphisme Humain) families. They could be ordered on chromosome 11 with an average distance of 2.1 cM. The tight correlation observed between the genetic order and the physical assignment of these microsatellites reinforces the genetic map data. These newly localized markers identified by the PCR method using a standardized protocol represent useful tools for mapping YAC clones and establishing YAC contigs and for studying genetic diseases or cancers associated with specific genes and/or germinal/somatic rearrangements of chromosome 11.

Mutations at the PAX6 locus are found in heterogeneous anterior segment malformations including Peters' anomaly

Mutation or deletion of the PAX6 gene underlies many cases of aniridia. Three lines of evidence now converge to implicate PAX6 more widely in anterior segment malformations including Peters' anomaly. First, a child with Peters' anomaly is deleted for one copy of PAX6. Second, affected members of a family with dominantly inherited anterior segment malformations, including Peters' anomaly are heterozygous for an R26G mutation in the PAX6 paired box. Third, a proportion of Sey/+ Smalleye mice, heterozygous for a nonsense mutation in murine Pax-6, have an ocular phenotype resembling Peters' anomaly. We therefore propose that a variety of anterior segment anomalies may be associated with PAX6 mutations.