Integration of a c-myc transgene results in disruption of the mouse Gtf2ird1 gene, the homologue of the human GTF2IRD1 gene hemizygously deleted in Williams-Beuren syndrome

ASIS-Seq: Transgene Insertion Site Mapping by Nanopore Adaptive Sampling

Generation of transgenic mice by direct microinjection of foreign DNA into fertilized ova has become a routine technique in biomedical research. It remains an essential tool for studying gene expression, developmental biology, genetic disease models, and their therapies. However, the random integration of foreign DNA into the host genome that is inherent to this technology can lead to confounding effects associated with insertional mutagenesis and transgene silencing. Locations of most transgenic lines remain unknown because the methods are often burdensome (Nicholls et al., G3: Genes Genomes Genetics 9:1481-1486, 2019) or have limitations (Goodwin et al., Genome Research 29:494-505, 2019). Here, we present a method that we call Adaptive Sampling Insertion Site Sequencing (ASIS-Seq) to locate transgene integration sites using targeted sequencing on Oxford Nanopore Technologies' (ONT) sequencers. ASIS-Seq requires only about 3 ug of genomic DNA, 3 hours of hands-on sample preparation time, and 3 days of sequencing time to locate transgenes in a host genome.

3R measures in facilities for the production of genetically modified rodents

Sociocultural changes in the human-animal relationship have led to increasing demands for animal welfare in biomedical research. The 3R concept is the basis for bringing this demand into practice: Replace animal experiments with alternatives where possible, Reduce the number of animals used to a scientifically justified minimum and Refine the procedure to minimize animal harm. The generation of gene-modified sentient animals such as mice and rats involves many steps that include various forms of manipulation. So far, no coherent analysis of the application of the 3Rs to gene manipulation has been performed. Here we provide guidelines from the Committee on Genetics and Breeding of Laboratory Animals of the German Society for Laboratory Animal Science to implement the 3Rs in every step during the generation of genetically modified animals. We provide recommendations for applying the 3Rs as well as success/intervention parameters for each step of the process, from experiment planning to choice of technology, harm-benefit analysis, husbandry conditions, management of genetically modified lines and actual procedures. We also discuss future challenges for animal welfare in the context of developing technologies. Taken together, we expect that our comprehensive analysis and our recommendations for the appropriate implementation of the 3Rs to technologies for genetic modifications of rodents will benefit scientists from a wide range of disciplines and will help to improve the welfare of a large number of laboratory animals worldwide.

Mapping the Chromosomal Insertion Site of the GFP Transgene of UBC-GFP Mice to the MHC Locus

GFP is frequently used as a marker for tracking donor cells adoptively transplanted into recipient animals. The human ubiquitin C promoter (UBC)-driven-GFP transgenic mouse is a commonly used source of donor cells for this purpose. This mouse was initially generated in the C57BL/6 inbred strain and has been backcrossed into the BALB/cBy strain for over 11 generations. Both the C57BL/6 inbred and BALB/cBy congenic UBC-GFP lines are commercially available and have been widely distributed. These UBC-GFP lines can be a convenient resource for tracking donor cells in both syngenic MHC-matched and in allogenic MHC-mismatched studies as C57BL/6 (H-2^b) and BALB/cBy (H-2^d) have disparate MHC haplotypes. In this report, we surprisingly discover that the UBC-GFP BALB/cBy congenic mice still retain the H-2^b MHC haplotype of their original C57BL/6 founder, suggesting that the UBC-GFP transgene integration site is closely linked to the MHC locus on chromosome 17. Using linear amplification-mediated PCR, we successfully map the UBC-GFP transgene to the MHC locus. This study highlights the importance and urgency of mapping the transgene integration site of transgenic mouse strains used in biomedical research. Furthermore, this study raises the possibility of alternative interpretations of previous studies using congenic UBC-GFP mice and focuses attention on the necessity for rigor and reproducibility in scientific research.

Defining Transgene Insertion Sites and Off-Target Effects of Homology-Based Gene Silencing Informs the Application of Functional Genomics Tools in Phytophthora infestans

DNA transformation and homology-based transcriptional silencing are frequently used to assess gene function in Phytophthora spp. Since unplanned side-effects of these tools are not well-characterized, we used P. infestans to study plasmid integration sites and whether knockdowns caused by homology-dependent silencing spread to other genes. Insertions occurred both in gene-dense and gene-sparse regions but disproportionately near the 5' ends of genes, which disrupted native coding sequences. Microhomology at the recombination site between plasmid and chromosome was common. Studies of transformants silenced for 12 different gene targets indicated that neighbors within 500 nt were often cosilenced, regardless of whether hairpin or sense constructs were employed and the direction of transcription of the target. However, this cis spreading of silencing did not occur in all transformants obtained with the same plasmid. Genome-wide studies indicated that unlinked genes with partial complementarity with the silencing-inducing transgene were not usually down-regulated. We learned that hairpin or sense transgenes were not cosilenced with the target in all transformants, which informs how screens for silencing should be performed. We conclude that transformation and gene silencing can be reliable tools for functional genomics in Phytophthora spp. but must be used carefully, especially by testing for the spread of silencing to genes flanking the target.

Efficient mapping of transgene integration sites and local structural changes in Cre transgenic mice using targeted locus amplification

Cre/LoxP technology is widely used in the field of mouse genetics for spatial and/or temporal regulation of gene function. For Cre lines generated via pronuclear microinjection of a Cre transgene construct, the integration site is random and in most cases not known. Integration of a transgene can disrupt an endogenous gene, potentially interfering with interpretation of the phenotype. In addition, knowledge of where the transgene is integrated is important for planning of crosses between animals carrying a conditional allele and a given Cre allele in case the alleles are on the same chromosome. We have used targeted locus amplification (TLA) to efficiently map the transgene location in seven previously published Cre and CreERT2 transgenic lines. In all lines, transgene insertion was associated with structural changes of variable complexity, illustrating the importance of testing for rearrangements around the integration site. In all seven lines the exact integration site and breakpoint sequences were identified. Our methods, data and genotyping assays can be used as a resource for the mouse community and our results illustrate the power of the TLA method to not only efficiently map the integration site of any transgene, but also provide additional information regarding the transgene integration events.

The transcription factor GTF2IRD1 regulates the topology and function of photoreceptors by modulating photoreceptor gene expression across the retina

The mechanisms that specify photoreceptor cell-fate determination, especially as regards to short-wave-sensitive (S) versus medium-wave-sensitive (M) cone identity, and maintain their nature and function, are not fully understood. Here we report the importance of general transcription factor II-I repeat domain-containing protein 1 (GTF2IRD1) in maintaining M cone cell identity and function as well as rod function. In the mouse, GTF2IRD1 is expressed in cell-fate determined photoreceptors at postnatal day 10. GTF2IRD1 binds to enhancer and promoter regions in the mouse rhodopsin, M- and S-opsin genes, but regulates their expression differentially. Through interaction with the transcription factors CRX and thyroid hormone receptor β 2, it enhances M-opsin expression, whereas it suppresses S-opsin expression; and with CRX and NRL, it enhances rhodopsin expression. In an apparent paradox, although GTF2IRD1 is widely expressed in multiple cell types across the retina, knock-out of GTF2IRD1 alters the retinal expression of only a limited number of annotated genes. Interestingly, however, the null mutation leads to altered topology of cone opsin expression in the retina, with aberrant S-opsin overexpression and M-opsin underexpression in M cones. Gtf2ird1-null mice also demonstrate abnormal M cone and rod electrophysiological responses. These findings suggest an important role for GTF2IRD1 in regulating the level and topology of rod and cone gene expression, and in maintaining normal retinal function.

Role of DLC1 tumor suppressor gene and MYC oncogene in pathogenesis of human hepatocellular carcinoma: potential prospects for combined targeted therapeutics (review)

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death, and its incidence is increasing worldwide in an alarming manner. The development of curative therapy for advanced and metastatic HCC is a high clinical priority. The HCC genome is complex and heterogeneous; therefore, the identification of recurrent genomic and related gene alterations is critical for developing clinical applications for diagnosis, prognosis and targeted therapy of the disease. This article focuses on recent research progress and our contribution in identifying and deciphering the role of defined genetic alterations in the pathogenesis of HCC. A significant number of genes that promote or suppress HCC cell growth have been identified at the sites of genomic reorganization. Notwithstanding the accumulation of multiple genetic alterations, highly recurrent changes on a single chromosome can alter the expression of oncogenes and tumor suppressor genes (TSGs) whose deregulation may be sufficient to drive the progression of normal hepatocytes to malignancy. A distinct and highly recurrent pattern of genomic imbalances in HCC includes the loss of DNA copy number (associated with loss of heterozygosity) of TSG-containing chromosome 8p and gain of DNA copy number or regional amplification of protooncogenes on chromosome 8q. Even though 8p is relatively small, it carries an unusually large number of TSGs, while, on the other side, several oncogenes are dispersed along 8q. Compelling evidence demonstrates that DLC1, a potent TSG on 8p, and MYC oncogene on 8q play a critical role in the pathogenesis of human HCC. Direct evidence for their role in the genesis of HCC has been obtained in a mosaic mouse model. Knockdown of DLC1 helps MYC in the induction of hepatoblast transformation in vitro, and in the development of HCC in vivo. Therapeutic interventions, which would simultaneously target signaling pathways governing both DLC1 and MYC functions in hepatocarcinogenesis, could result in progress in the treatment of liver cancer.

Mutation of Gtf2ird1 from the Williams-Beuren syndrome critical region results in facial dysplasia, motor dysfunction, and altered vocalisations

Insufficiency of the transcriptional regulator GTF2IRD1 has become a strong potential explanation for some of the major characteristic features of the neurodevelopmental disorder Williams-Beuren syndrome (WBS). Genotype/phenotype correlations in humans indicate that the hemizygous loss of the GTF2IRD1 gene and an adjacent paralogue, GTF2I, play crucial roles in the neurocognitive and craniofacial aspects of the disease. In order to explore this genetic relationship in greater detail, we have generated a targeted Gtf2ird1 mutation in mice that blocks normal GTF2IRD1 protein production. Detailed analyses of homozygous null Gtf2ird1 mice have revealed a series of phenotypes that share some intriguing parallels with WBS. These include reduced body weight, a facial deformity resulting from localised epidermal hyperplasia, a motor coordination deficit, alterations in exploratory activity and, in response to specific stress-inducing stimuli; a novel audible vocalisation and increased serum corticosterone. Analysis of Gtf2ird1 expression patterns in the brain using a knock-in LacZ reporter and c-fos activity mapping illustrates the regions where these neurological abnormalities may originate. These data provide new mechanistic insight into the clinical genetic findings in WBS patients and indicate that insufficiency of GTF2IRD1 protein contributes to abnormalities of facial development, motor function and specific behavioural disorders that accompany this disease.

Animal models of Williams syndrome

In recent years, researchers have generated a variety of mouse models in an attempt to dissect the contribution of individual genes to the complex phenotype associated with Williams syndrome (WS). The mouse genome is easily manipulated to produce animals that are copies of humans with genetic conditions, be it with null mutations, hypomorphic mutations, point mutations, or even large deletions encompassing many genes. The existing mouse models certainly seem to implicate hemizygosity for ELN, BAZ1B, CLIP2, and GTF2IRD1 in WS, and new mice with large deletions of the WS region are helping us to understand both the additive and potential combinatorial effects of hemizygosity for specific genes. However, not all genes that are haploinsufficient in humans prove to be so in mice and the effect of genetic background can also have a significant effect on the penetrance of many phenotypes. Thus although mouse models are powerful tools, the information garnered from their study must be carefully interpreted. Nevertheless, mouse models look set to provide a wealth of information about the neuroanatomy, neurophysiology and molecular pathways that underlie WS and in the future will act as essential tools for the development and testing of therapeutics.

Negative autoregulation of GTF2IRD1 in Williams-Beuren syndrome via a novel DNA binding mechanism

The GTF2IRD1 gene is of principal interest to the study of Williams-Beuren syndrome (WBS). This neurodevelopmental disorder results from the hemizygous deletion of a region of chromosome 7q11.23 containing 28 genes including GTF2IRD1. WBS is thought to be caused by haploinsufficiency of certain dosage-sensitive genes within the deleted region, and the feature of supravalvular aortic stenosis (SVAS) has been attributed to reduced elastin caused by deletion of ELN. Human genetic mapping data have implicated two related genes GTF2IRD1 and GTF2I in the cause of some the key features of WBS, including craniofacial dysmorphology, hypersociability, and visuospatial deficits. Mice with mutations of the Gtf2ird1 allele show evidence of craniofacial abnormalities and behavioral changes. Here we show the existence of a negative autoregulatory mechanism that controls the level of GTF2IRD1 transcription via direct binding of the GTF2IRD1 protein to a highly conserved region of the GTF2IRD1 promoter containing an array of three binding sites. The affinity for this protein-DNA interaction is critically dependent upon multiple interactions between separate domains of the protein and at least two of the DNA binding sites. This autoregulatory mechanism leads to dosage compensation of GTF2IRD1 transcription in WBS patients. The GTF2IRD1 promoter represents the first established in vivo gene target of the GTF2IRD1 protein, and we use it to model its DNA interaction capabilities.

More than the sum of its parts: new mouse models for dissecting the genetic complexities of Williams-Beuren syndrome

Psychiatric disorders are a common, severe and disabling group of diseases where progress in finding novel molecular targets has been slow. This is partly due to our lack of understanding of the molecular pathophysiology of these conditions as they play out in the brain (Insel & Scolnick, 2006). Since many of these diseases (such as schizophrenia, bipolar disorder or autism) are highly heritable, a genetic approach to dissecting the risk architecture is a promising avenue for molecular medicine; however, variants in single genes frequently present in the population have only small to moderate effects on complex behavioural phenotypes (O'Donovan et al, 2008).

Recurrent and nonrandom DNA copy number and chromosome alterations in Myc transgenic mouse model for hepatocellular carcinogenesis: implications for human disease

Mouse models for hepatocellular carcinoma (HCC) provide an experimental ground for dissecting the genetic and biological complexities of human liver cancer and contribute to our ability to gain insights into the relevance of candidate cancer genes. We examined, using spectral karyotyping (SKY) and array-based CGH (aCGH), seven cell lines derived from HCC spontaneously developed in transgenic Myc mice (Myc), and four cell lines established from tumors induced in nude mice by inoculation with the original Myc cells (nuMyc). All the cell lines exhibited gain of material from chromosomes 5, 6, 8, 10, 11, 15, and 19 and DNA copy-number loss from chromosomes 2, 4, 7, 9, 12, 14, and X. In addition, several recurrent chromosome reorganizations were found, including del(3), t(3;8), del(4), t(4;11), t(6;5), del(7), del(8), del(9), t(10;14), del(11), and del(16). Chromosome breakpoints underlying rearrangements clustered in the regions previously identified as important for the early stages of Myc-induced hepatocarcinogenesis. The results strongly suggest the importance of recurrent breakage and loss of chromosomes 4, 9, and 14 and gain of chromosomes 15 and 19 in mouse liver neoplasia. Genomic changes observed in Myc HCC cell lines are also recurrent in HCC developed in other transgenic mouse models, in mouse spontaneous HCC and derivative cell lines, and in preneoplastic liver lesions induced with chemical carcinogens. Overall, the present results document selective, nonrandom genomic changes involving chromosomal regions homologous to those implicated in human HCC.

A genome-wide screen for modifiers of transgene variegation identifies genes with critical roles in development

An extended ENU screen for modifiers of transgene variegation identified four new modifiers, MommeD7-D10.

Background

Some years ago we established an N-ethyl-N-nitrosourea screen for modifiers of transgene variegation in the mouse and a preliminary description of the first six mutant lines, named MommeD1-D6, has been published. We have reported the underlying genes in three cases: MommeD1 is a mutation in SMC hinge domain containing 1 (Smchd1), a novel modifier of epigenetic gene silencing; MommeD2 is a mutation in DNA methyltransferase 1 (Dnmt1); and MommeD4 is a mutation in Smarca 5 (Snf2h), a known chromatin remodeler. The identification of Dnmt1 and Smarca5 attest to the effectiveness of the screen design.

Results

We have now extended the screen and have identified four new modifiers, MommeD7-D10. Here we show that all ten MommeDs link to unique sites in the genome, that homozygosity for the mutations is associated with severe developmental abnormalities and that heterozygosity results in phenotypic abnormalities and reduced reproductive fitness in some cases. In addition, we have now identified the underlying genes for MommeD5 and MommeD10. MommeD5 is a mutation in Hdac1, which encodes histone deacetylase 1, and MommeD10 is a mutation in Baz1b (also known as Williams syndrome transcription factor), which encodes a transcription factor containing a PHD-type zinc finger and a bromodomain. We show that reduction in the level of Baz1b in the mouse results in craniofacial features reminiscent of Williams syndrome.

Conclusions

These results demonstrate the importance of dosage-dependent epigenetic reprogramming in the development of the embryo and the power of the screen to provide mouse models to study this process.

Reduced fear and aggression and altered serotonin metabolism in Gtf2ird1-targeted mice

The GTF2IRD1 general transcription factor is a candidate for involvement in the varied cognitive and neurobehavioral symptoms of the microdeletion disorder, Williams-Beuren syndrome (WBS). We show that mice with heterozygous or homozygous disruption of Gtf2ird1 exhibit decreased fear and aggression and increased social behaviors. These findings are reminiscent of the hypersociability and diminished fear of strangers that are hallmarks of WBS. Other core features of WBS, such as increased anxiety and problems with spatial learning were not present in the targeted mice. Investigation of a possible neurochemical basis for the altered behaviors in these mice using high-performance liquid chromatography analysis showed increased levels of serotonin metabolites in several brain regions, including the amygdala, frontal cortex and parietal cortex. Serotonin levels have previously been implicated in fear and aggression, through modulation of the neural pathway connecting the prefrontal cortex and amygdala. These results suggest that hemizygosity for GTF2IRD1 may play a role in the complex behavioral phenotype seen in patients with WBS, either individually, or in combination with other genes, and that the GTF2I transcription factors may influence fear and social behavior through the alteration of neurochemical pathways.

Contribution of CYLN2 and GTF2IRD1 to neurological and cognitive symptoms in Williams Syndrome

Williams Syndrome (WS, [MIM 194050]) is a disorder caused by a hemizygous deletion of 25-30 genes on chromosome 7q11.23. Several of these genes including those encoding cytoplasmic linker protein-115 (CYLN2) and general transcription factors (GTF2I and GTF2IRD1) are expressed in the brain and may contribute to the distinct neurological and cognitive deficits in WS patients. Recent studies of patients with partial deletions indicate that hemizygosity of GTF2I probably contributes to mental retardation in WS. Here we investigate whether CYLN2 and GTF2IRD1 contribute to the motoric and cognitive deficits in WS. Behavioral assessment of a new patient in which STX1A and LIMK1, but not CYLN2 and GTF2IRD1, are deleted showed that his cognitive and motor coordination functions were significantly better than in typical WS patients. Comparative analyses of gene specific CYLN2 and GTF2IRD1 knockout mice showed that a reduced size of the corpus callosum as well as deficits in motor coordination and hippocampal memory formation may be attributed to a deletion of CYLN2, while increased ventricle volume can be attributed to both CYLN2 and GTF2IRD1. We conclude that the motor and cognitive deficits in Williams Syndrome are caused by a variety of genes and that heterozygous deletion of CYLN2 is one of the major causes responsible for such dysfunctions.

Expression of Gtf2ird1, the Williams syndrome-associated gene, during mouse development

The gene GTF2IRD1 is localized within the critical region on chromosome 7 that is deleted in Williams syndrome patients. Genotype-phenotype comparisons of patients carrying variable deletions within this region have implicated GTF2IRD1 and a closely related homolog, GTF2I, as prime candidates for the causation of the principal symptoms of Williams syndrome. We have generated mice with an nls-LacZ knockin mutation of the Gtf2ird1 allele to study its functional role and examine its expression profile. In adults, expression is most prominent in neurons of the central and peripheral nervous system, the retina of the eye, the olfactory epithelium, the spiral ganglion of the cochlea, brown fat adipocytes and to a lesser degree myocytes of the heart and smooth muscle. During development, a dynamic pattern of expression is found predominantly in musculoskeletal tissues, the pituitary, craniofacial tissues, the eyes and tooth buds. Expression of Gtf2ird1 in these tissues correlates with the manifestation of some of the clinical features of Williams syndrome.

Neural mechanisms in Williams syndrome: a unique window to genetic influences on cognition and behaviour

Williams syndrome, a rare disorder caused by hemizygous microdeletion of about 28 genes on chromosome 7q11.23, has long intrigued neuroscientists with its unique combination of striking behavioural abnormalities, such as hypersociability, and characteristic neurocognitive profile. Williams syndrome, therefore, raises fundamental questions about the neural mechanisms of social behaviour, the modularity of mind and brain development, and provides a privileged setting to understand genetic influences on complex brain functions in a 'bottom-up' way. We review recent advances in uncovering the functional and structural neural substrates of Williams syndrome that provide an emerging understanding of how these are related to dissociable genetic contributions characterized both in special participant populations and animal models.

GTF2IRD1 in craniofacial development of humans and mice

Craniofacial abnormalities account for about one-third of all human congenital defects, but our understanding of the genetic mechanisms governing craniofacial development is incomplete. We show that GTF2IRD1 is a genetic determinant of mammalian craniofacial and cognitive development, and we implicate another member of the TFII-I transcription factor family, GTF2I, in both aspects. Gtf2ird1-null mice exhibit phenotypic abnormalities reminiscent of the human microdeletion disorder Williams-Beuren syndrome (WBS); craniofacial imaging reveals abnormalities in both skull and jaws that may arise through misregulation of goosecoid, a downstream target of Gtf2ird1. In humans, a rare WBS individual with an atypical deletion, including GTF2IRD1, shows facial dysmorphism and cognitive deficits that differ from those of classic WBS cases. We propose a mechanism of cumulative dosage effects of duplicated and diverged genes applicable to other human chromosomal disorders.

Disruption of beta-catenin pathway or genomic instability define two distinct categories of liver cancer in transgenic mice

BACKGROUND & AIMS

Human liver cancer can be divided into 2 categories that are characterized by activation of beta-catenin and genomic instability. Here we investigate whether similar categories exist among 5 transgenic models of liver cancer, including c-myc, transforming growth factor-alpha, E2F-1, c-myc/transforming growth factor-alpha, and c-myc/E2F-1 mice.

METHODS

The random amplified polymorphic DNA method was used to assess the overall genomic instability, and chromosomal loci affected by genomic alterations were determined by microsatellite analysis. beta-Catenin mutations and deletions were analyzed by polymerase chain reaction and sequencing screening. Cellular localization of beta-catenin and expression of alpha-fetoprotein, a prognostic marker of hepatocellular carcinoma, were investigated by immunohistochemistry.

RESULTS

Liver tumors from the transgenic mice could be divided into 2 broad categories characterized by extensive genomic instability (exemplified by the c-myc/transforming growth factor-alpha mouse) and activation of beta-catenin (exemplified by the c-myc/E2F-1 mouse). The c-myc/transforming growth factor-alpha tumors displayed extensive genomic instability with recurrent loss of heterozygosity at chromosomes 1, 2, 4, 6, 7, 9, 12, 14, and X and a low rate of beta-catenin activation. The genomic instability was evident from the early dysplastic stage and occurred concomitantly with increased expression of alpha-fetoprotein. The c-myc/E2F-1 tumors were characterized by a high frequency of beta-catenin activation in the presence of a relatively stable genome and low alpha-fetoprotein levels.

CONCLUSIONS

We have identified 2 prototype experimental models, i.e., c-myc/transforming growth factor-alpha and c-myc/E2F-1 mice, for the 2 categories of human hepatocellular carcinoma characterized by genomic instability and beta-catenin activation, respectively. These mouse models will assist in the elucidation of the molecular basis of human hepatocellular carcinoma.

Síndrome de Williams-Beuren: presentación de 82 casos

OBJECTIVE

We performed a retrospective review of a series of 82 cases of Williams-Beuren syndrome (WBS) and associated diseases.

MATERIAL AND METHODS

A series of 82 patients (47 males and 35 females) who consulted at the hospital because of mental retardation and/or congenital cardiopathy were included. The patients were studied mainly from a neurological and cardiological point of view, and secondarily because of endocrinological and nephrological problems. Since description of the chromosomal abnormalities provoking the syndrome, we perform karyotyping in all patients with suspected WBS.

RESULTS

Alterations mainly consisted of distinctive facial appearance (100 %), mental retardation with friendly behavior (90 %), congenital cardiopathy (85.4 %), mostly consisting of supravalvular aortic stenosis (72 %), with (12 %) or without (60 %) pulmonary stenosis, and behavior typical of attention deficit-hyperactivity disorder, which usually manifested at the age of 4 to 5 years in both boys and girls. Approximately 90 % started to walk and speak later than average. Birthweight was below 3000 g in 65 % of the patients in whom this datum was included in the medical record. Eleven of the 13 patients (84.5 %) studied showed the typical deletion of WBS.

CONCLUSION

Study of patients with WBS should be multidisciplinary. Most patients require help during schooling and subsequent vocational guidance.

Williams-Beuren syndrome: a model of recurrent genomic mutation

Williams-Beuren syndrome is a segmental aneusomy syndrome with manifestations affecting the vascular, connective tissue, endocrine and central nervous systems. Most patients show a similar heterozygous approximately 1.5 Mb deletion at 7q11.23 that contains a number of reported genes. Deletion mapping in the few atypical patients with smaller deletions suggested that additive effects of haploinsufficiency for two or more genes might be necessary for the phenotype. Vascular stenoses are caused by haploinsufficiency at the elastin gene, while the genes responsible for the cognitive deficits are likely located at the telomeric edge of the deletion, including CYLN2 and GTF2I. Large region-specific segmental duplications predispose to misalignment and inter- or intrachromosomal unequal crossing-over causing the deletions. Atypical alleles at 7q11.23 such as inversions and deletions/insertions of large repeats, also generated through aberrant recombination between the local segmental duplications, are found in approximately 35% of transmitting parents. Genomic instability at 7q11.23 is directly related to the genomic structure of the region.

Williams-Beuren syndrome: a challenge for genotype-phenotype correlations

Many human chromosomal abnormality syndromes include specific cognitive and behavioural components. Children with Prader-Willi syndrome lack a paternally derived copy of the proximal long arm of chromosome 15, and eat uncontrollably; in Angelman syndrome lack of a maternal contribution of 15q11-q13 results in absence of speech, frequent smiling and episodes of paroxysmal laughter; deletions on 22q11 can be associated with obsessive behaviour and schizophrenia. The neurodevelopmental disorder Williams-Beuren syndrome (WBS), is caused by a microdeletion at 7q11.23 and provides us with one of the most convincing models of a relationship that links genes with human cognition and behaviour. The hypothesis is that deletion of one or a series of genes causes neurodevelopmental abnormalities that manifest as the fractionation of mental abilities typical of WBS. Detailed molecular characterization of the deletion alongside well-defined cognitive profiling in WBS provides a unique opportunity to investigate the neuromolecular basis of complex cognitive behaviour, and develop integrated approaches to study gene function and genotype-phenotype correlations.

Expression of BEN, a member of TFII-I family of transcription factors, during mouse pre- and postimplantation development

BEN is a member of the TFII-I family of transcription factors, characterized by the presence of multiple helix-loop-helix repeat domains. Our immunohistochemical analysis demonstrated broad and extensive expression of BEN during mouse pre- and postimplantation development, with highest levels occurring during early to midgestation. Maternally expressed BEN is present in both the cytoplasm and nuclei of the zygote; however, it retains a predominantly nuclear localization between the two-cell stage of development and early blastocyst stages. This nuclear expression is observed in most tissues throughout development. Although, it is interesting to note that at E4.5-6.5, during early gastrulation stage, BEN is localized in the cytoplasm. At later stages, BEN retains an extensive expression pattern in a variety of developing systems implicating its involvement in tissue development and organogenesis.

Graded phenotypic response to partial and complete deficiency of a brain-specific transcript variant of the winged helix transcription factor RFX4

One line of mice harboring a cardiac-specific epoxygenase transgene developed head swelling and rapid neurological decline in young adulthood, and had marked hydrocephalus of the lateral and third ventricles. The transgene was found to be inserted into an intron in the mouse Rfx4 locus. This insertion apparently prevented expression of a novel variant transcript of RFX4 (RFX4_v3), a member of the regulatory factor X family of winged helix transcription factors. Interruption of two alleles resulted in profound failure of dorsal midline brain structure formation and perinatal death, presumably by interfering with expression of downstream genes. Interruption of a single allele prevented formation of the subcommissural organ, a structure important for cerebrospinal fluid flow through the aqueduct of Sylvius, and resulted in congenital hydrocephalus. These data implicate the RFX4_v3 variant transcript as being crucial for early brain development, as well as for the genesis of the subcommissural organ. These findings may be relevant to human congenital hydrocephalus, a birth defect that affects approximately 0.6 per 1000 newborns.

Metaphase FISHing of transgenic mice recommended: FISH and SKY define BAC-mediated balanced translocation

The evolving trend to use larger transgenes and their associated increased chance of unexpected genetic events mandates more careful characterization of transgenic mice. In characterizing our five new mouse strains transgenic for the BAC, bEMS4, we have identified the highest copy number reported to date: the stable incorporation of approximately 40 copies of a 194-kb expressed transgene in a single insertion site. We caution, however, that standard molecular techniques failed to identify a balanced translocation in another strain, and an inappropriate site of insertion in a third. Molecular cytogenetic analysis using metaphase FISH was the minimum level of characterization needed to reveal these unexpected genetic events. In addition, we combined FISH and SKY to identify the transgene at the breakpoints of the balanced translocation, t(3;9). This is the first description of a BAC-mediated chromosomal rearrangement and the first application of SKY to identify transgene-induced chromosomal rearrangements.

Gene structure, tissue expression, and linkage mapping of the mouse DLC-1 gene (Arhgap7)

DLC-1 (deleted in liver cancer 1) is a candidate tumor suppressor gene for hepatocellular carcinoma and other cancers. It is the human homologue of rat p122, which has been shown to function as a GTPase activating protein for RhoA, and it may be involved in signal transduction pathways regulating cell proliferation and adhesion. To establish an animal model for studying the regulation and function of DLC-1, we have undertaken the characterization of the mouse DLC-1 gene. Northern blot analysis shows that the mouse DLC-1 mRNA is widely expressed, with the highest levels in heart, liver, and lung. Mouse genomic clones that contain the entire DLC-1 gene of 47 kb were isolated. The mouse gene consists of 14 exons, and the structural organization is highly similar to that of the human gene. The promoter region of the mouse gene was GC-rich and contained potential binding sites for transcription factors SP1, GCF, and AP-2. A polymorphic microsatellite marker in intron 8 was used for mapping the gene (Arhgap7) to 20 cM on mouse chromosome 8 and for allelotyping of mouse liver tumor DNAs.

Genomic organization of the genes Gtf2ird1, Gtf2i, and Ncf1 at the mouse chromosome 5 region syntenic to the human chromosome 7q11.23 Williams syndrome critical region

We have recently isolated a mouse ortholog of human GTF2IRD1 that is related to GTF2I. GTF2IRD1 and GTF2I proteins are characterized by the presence of multiple helix-loop-helix domains and a leucine zipper motif. Both paralogs are closely linked and deleted hemizygously in individuals with Williams syndrome, a dominant genetic condition characterized by unique neurocognitive and behavioral features. We have isolated and analyzed the sequence of bacterial artificial chromosome clones from the syntenic mouse chromosome 5 region that contains Gtf2ird1 and Gtf2i as well as a neighboring gene, Ncf1. Gtf2ird1 is composed of 31 exons spanning >100 kb on mouse chromosome 5 and is located between Cyln2 and Gtf2i. Gtf2i is composed of 34 exons spanning about 77 kb. Ncf1, located downstream of Gtf2i, consists of 11 exons that extend over 8 kb. The gene organization of Gtf2ird1, Gtf2i, and Ncf1 is conserved in mice and humans, although the intronic regions are more compact in the mouse genome. The helix-loop-helix repeats of Gtf2ird1 and Gtf2i are encoded separately on adjacent exons and were generated by independent genomic rearrangements. These studies contribute to our knowledge of transcription factor defects and their pathogenesis in haploinsufficiency conditions.

Biochemistry and biology of the inducible multifunctional transcription factor TFII-I

An animal cell has the capability to respond to a variety of external signals through cell surface receptors. The response is usually manifested in terms of altered gene expression in the nucleus. Thus, in modern molecular and cell biology, it has become important to understand how the communication between extracellular signals and nuclear gene transcription is achieved. Originally discovered as a basal factor required for initiator-dependent transcription in vitro, recent evidence suggests that TFII-I is also an inducible multifunctional transcription factor that is activated in response to a variety of extracellular signals and translocates to the nucleus to turn on signal-induced genes. Here I review the biochemical and biological properties of TFII-I and related proteins in nuclear gene transcription, signal transduction and genetic disorders.