Expression of Expanded Polyglutamine Protein Induces Behavioral Changes in Drosophila (Polyglutamine-Induced Changes in Drosophila)

Spinocerebellar ataxia type-3 or Machado-Joseph disease (SCA3/MJD) is an autosomal dominant neurodegenerative disease caused by triplet nucleotide expansion. The expansion of the polyglutamine tract near the C terminus of the MJD1 gene product, ataxin-3, above a threshold of 40 glutamine repeats causes neuronal loss and degeneration. The expanded ataxin-3 forms aggregates, and nuclear inclusions, within neurons, possibly due to the misfolding of mutant proteins. Here we report upon the behavioral test changes related to truncated and expanded forms of MJD protein (MJDtr) in Drosophila, and show that expanded MJDtr, when expressed in the nervous system, causes characteristic locomotor dysfunction and anosmia. This phenomenon has not been previously reported in humans or in transgenic Drosophila models. In addition, the in vivo expression of the antiapoptotic gene bcl-2 showed no evidence of ameliorating the deleterious effect of MJDtr-Q78s, either in the eye or in the nervous system. The study shows that such Drosophila transgenic models express olfactory dysfunction and ataxic behavior as observed in human patients.

Silencing the Drosophila ribosomal protein L14 gene using targeted RNA interference causes distinct somatic anomalies

The Drosophila Minutes are haploinsufficient mutations that are defective in ribosomal protein (rp) production, resulting in short, thin bristles, delayed development and recessive lethality. In a Minute fly, the amount of rp gene messenger RNA (mRNA) is reduced to >or=50% of the normal amount of gene product, and becomes rate limiting for ribosome biogenesis, cell proliferation and growth. Haploinsufficiency increases the vulnerability to complete loss of gene function (homozygous null state) if hit by a second mutation. Because of the homozygous lethality, it has only been possible to study the effects of Minute mutations in heterozygous animals. To be able to study the consequences of a loss-of-function of an rp gene (0%>mRNA<50%) in developing and differentiated cells we used heritable RNA interference (RNAi) in combination with the yeast GAL4/UAS binary system to spatiotemporally knock down the ribosomal protein L14 (RpL14) gene. We show, at the RNA and phenotypic levels, that RNAi efficiently reduces RpL14 gene expression throughout development, causing lethality and distinct and dramatic somatic anomalies in both developing and differentiated cells.

Inactivation of mouse Twisted gastrulation reveals its role in promoting Bmp4 activity during forebrain development

Twisted gastrulation (Tsg) is a secreted protein that regulates Bmp signaling in the extracellular space through its direct interaction with Bmp/Dpp and Chordin (Chd)/Short gastrulation (Sog). The ternary complex of Tsg/Chd/Bmp is cleaved by the metalloprotease Tolloid (Tld)/Xolloid (Xld). Studies in Drosophila, Xenopus and zebrafish suggest that Tsg can act both as an anti-Bmp and as a pro-Bmp. We have analyzed Tsgloss-of-function in the mouse. Tsg homozygous mutants are viable but of smaller size and display mild vertebral abnormalities and osteoporosis. We provide evidence that Tsg interacts genetically with Bmp4. When only one copy of Bmp4 is present, a requirement of Tsgfor embryonic development is revealed. Tsg-/-;Bmp4+/- compound mutants die at birth and display holoprosencephaly, first branchial arch and eye defects. The results show that Tsg functions to promote Bmp4 signaling during mouse head development.

[Effect of parental age on endoreduplication of giant chromosomes and some quantitative traits in Drosophila melanogaster descendants]

We studied the influence of parental age on the degree of polyteny of giant chromosomes and expressivity of mutation eyeless in Drosophila melanogaster descendants. The parental age equal to six days exerted an adverse effect on the function of endoreduplication of giant chromosomes in strain eyeless. The highest degree of polyteny was observed in descendants of four- and ten-day imago. The maximum reduction of eye facets was observed in descendants of four-day imago, while in the progeny of older parents, the mutation expressivity was sharply reduced. Relations between the changes in chromosome polyteny, expressivity of mutation eyeless, and earlier studied components of adaptation were statistically analyzed in descendants of aging parents of this Drosophila strain.

POMGnT1 gene alterations in a family with neurological abnormalities

Muscle-eye-brain disease (MEB), is caused by mutations in the POMGnT1 gene. We describe a white family with two siblings affected with congenital hypotonia early-onset glaucoma, and psychomotor delays. Brain magnetic resonance images (MRIs) showed hydrocephalus, bilateral frontal polymicrogyria, abnormal cerebellum, and characteristic flattened dystrophic pons. We identified novel POMGnT1 gene alterations in this family. Both affected siblings were found to be compound hetrozygotes and carried two missense changes inherited from their mother and one missense change (p.R442C) inherited from their father. Our findings further define the phenotypic spectrum of MEB and its occurrence in the US population.

Primary megalocornea: clinical features for differentiation from infantile glaucoma

PURPOSE

To describe the ocular findings in megalocornea to assist in its differentiation from infantile glaucoma in the evaluation of children with abnormally enlarged corneas.

METHODS

The clinical findings of 4 boys found to have megalocornea following referral for evaluation of large corneas and suspected glaucoma were reviewed.

RESULTS

Three of the 4 patients had photophobia. Clear and enlarged corneas were observed associated with deep anterior chambers, posterior bowing of the irides, and normal intraocular pressures (IOPs) in all eyes. Transillumination of the irides was found in 6 of 8 eyes and pigment dispersion was seen in 4 of 8 eyes. Pigment dispersion appeared to be acquired over time, and the youngest patient in this series who had pigment dispersion detected on slit-lamp examination was 15 years; the youngest patient with the condition detected on gonioscopy was 8 years. No breaks in Descemet's membrane were present. Family history obtained from 3 of the 4 patients revealed evidence of sex-linked recessive inheritance. These findings are distinct from the clinical features of infantile glaucoma characterized by elevated IOP, breaks in Descemet's membrane, corneal edema, a generally flat iris profile, less pronounced enlargement of the anterior segment, the absence of iris transillumination and pigment dispersion, and autosomal recessive inheritance. Three patients had corneal size asymmetry, a finding that has not been previously reported.

CONCLUSION

Hereditary megalocornea has defining clinical findings that help to identify and differentiate it from other causes of enlarged corneas. Asymmetry in corneal size does not preclude its diagnosis.

Distal arthrogryposis type IIB: Unreported ophthalmic findings

We describe four members spanning three generations of a Caucasian family affected with distal arthrogryposis (DA). Based on Hall's original classification, we have placed our family under type IIB and present previously unreported ophthalmic features. All the members had different degrees of ophthalmoplegia, ptosis, astigmatism, and strabismus. Other findings in affected family members included keratoconus in the index patient, which was associated with abnormal electron microscopy of the affected cornea and increased thickness of the central cornea, small axial length of the globe and choroidal folds in the others.

Relation between oculo-auriculo-vertebral (OAV) dysplasia and three other non-random associations of malformations (VATER, CHARGE, and OEIS)

Using a statistical methodology, we aimed to identify a group of probable cases of oculo-auriculo-vertebral (OAV) dysplasia and to investigate possible relationships between different patterns of congenital malformations. Among 5,260 infants with multiple malformations collected from 4 large registers of congenital malformations, we identified 312 probable OAV cases. With the same technique, we have earlier defined epidemiological delineations of three other well-known non-random associations of congenital malformations (CHARGE, VATER, and OEIS). We found convincing relationships between OAV and VATER or CHARGE but none between OAV and OEIS or between the three malformation complexes CHARGE, VATER, and OEIS. An association between two conditions indicates similarities in pathogenesis or in etiology. We suggest that the connection between OAV and CHARGE could be related to a common pathogenetic mechanism: disturbed neural crest development.

PAX6 and congenital eye malformations

The PAX6 gene is a paradigm for our understanding of the molecular genetics of mammalian eye development. Twelve years after its identification it is one of the most intensively studied genes, both in terms of its diverse and complex functions during oculogenesis and its role in an ever-increasing variety of human congenital eye malformations. The PAX6 field has benefited greatly from the continued input of clinicians, human geneticists and developmental biologists. This review summarizes the latest data on the PAX6 mutation spectrum and recent insights into Pax6 function from the mouse.

Aicardi syndrome

The astute observations of Aicardi and colleagues led to the first description of Aicardi syndrome as a triad of infantile spasms, absence of the corpus callosum, and chorioretinal lacunae. Still diagnosed clinically, we now recognize an expanded version of this probable X-linked dominant disorder that predominantly affects females. In addition to the classic findings, patients typically experience intractable epilepsy of multiple seizure types, profound mental retardation, and costovertebral anomalies. Associated cerebral and ophthalmologic malformations are numerous. This article highlights several seminal citations involving the history of the initial description and the characteristic ophthalmologic and electroencephalographic features of Aicardi syndrome.

Phospholipid membrane composition affects EGF receptor and Notch signaling through effects on endocytosis during Drosophila development

The role of phospholipids in the regulation of membrane trafficking and signaling is largely unknown. Phosphatidylcholine (PC) is a main component of the plasma membrane. Mutants in the Drosophila phosphocholine cytidylyltransferase 1 (CCT1), the rate-limiting enzyme in PC biosynthesis, show an altered phospholipid composition with reduced PC and increased phosphatidylinositol (PI) levels. Phenotypic features of dCCT1 indicate that the enzyme is not required for cell survival, but serves a role in endocytic regulation. CCT1- cells show an increase in endocytosis and enlarged endosomal compartments, whereas lysosomal delivery is unchanged. As a consequence, an increase in endocytic localization of EGF receptor (Egfr) and Notch is observed, and this correlates with a reduction in signaling strength and leads to patterning defects. A further link between PC/PI content, endocytosis, and signaling is supported by genetic interactions of dCCT1 with Egfr, Notch, and genes affecting endosomal traffic.

Eye birth defects in humans may be caused by a recessively-inherited genetic predisposition to the effects of maternal vitamin A deficiency during pregnancy

Congenital malformations of the eye can cause blindness in children. They occur throughout the world and in most cases the aetiology is unknown. Linkage studies have largely been unsuccessful and the risk to siblings is generally low. Epidemiological and laboratory evidence support a hypothesis that there may be genetic (recessive) predisposition to the teratogenetic effects of mild to moderate maternal vitamin A deficiency (VAD) during pregnancy. This may explain the higher prevalence of congenital eye anomalies in a part of Asian countries, where maternal VAD is common and consanguineous marriages are popular. Other congenital malformations commonly found in association with ocular coloboma (e.g. oesophageal fistulae and heart defects in CHARGE association) may also be VAD related. Mutations in a gene involved in the cellular access to vitamin A that normally protects the tissue or embryo from natural variation in dietary vitamin A intake, could render that individual intolerant of conditions of VAD. An interaction of this kind could also explain a proportion of "sporadic" cases in locations where VAD is uncommon. If this interaction is shown to be true, there are public health implications for the prevention of blindness due to congenital eye malformations. The hypotheses proposed above are reminiscent of the research leading to the discovery that folic acid supplementation could prevent neural tube defects. However, this form of intervention would be much more difficult with vitamin A, which is itself a powerful teratogen if present in excess.

The genetic and molecular basis of congenital eye defects

The mature eye is a complex organ that develops through a highly organized process during embryogenesis. Alterations in its genetic programming can lead to severe disorders that become apparent at birth or shortly afterwards; for example, one-half of the cases of blindness in children have a genetic cause. This review outlines the genetic basis of eye development, as determined by mutation analysis in patients and in model organisms. A better understanding of how this intricate organ develops at the genetic and cellular level is central to our understanding of the pathologies that afflict it.

Identification and Analysis of a Novel Mutation in the FOXC1 Forkhead Domain

PURPOSE

To determine the genetic and biochemical defects that underlie Axenfeld-Rieger malformations, identify the pathogenic mutation causing these malformations, and understand how these mutations alter protein function.

METHODS

FOXC1 was amplified from a proband with Axenfeld-Rieger malformations and the proband's mother. PCR products were sequenced to identify the pathogenic mutation. Site-directed mutagenesis was used to introduce this mutation into the FOXC1 cDNA. A synthetic mutation at the same position was also introduced, and both natural and synthetic proteins were tested for their ability to localize to the nucleus, bind DNA, and transactivate gene expression.

RESULTS

A novel missense mutation (L86F) was identified in FOXC1 in this family. The mutation is located in alpha-helix 1 of the forkhead domain. Biochemical assays showed that the L86F mutation does not affect nuclear localization of FOXC1, but reduces DNA binding and significantly reduces transactivation. The severity of the disruption to FOXC1 protein activity does not appear to correspond well with the severity of the phenotype in the patient. Analogous studies using a L86P, a known alpha-helix breaker, severely disrupts FOXC1 function, revealing the importance of helix 1 in FOXC1 structure and function.

CONCLUSIONS

A novel mutation in helix 1 of the FOXC1 forkhead domain has been identified and the importance of position 86 in FOXC1 activity demonstrated. These studies also identified the role of helix 1 in FOXC1 function and provide further evidence for the lack of strong genotype-phenotype correlation in FOXC1 pathogenesis. Normal development appears to be dependent on tight upper and lower thresholds of FOXC1 activity.

Mutation of the FOXC2 gene in familial distichiasis

OBJECTIVE

To examine the FOXC2 gene in a family with hereditary distichiasis.

BACKGROUND

Distichiasis, ie, a second row of eyelashes arising from the meibomian glands of the eyelids, can be inherited either alone (Online Mendelian Inheritance in Man [OMIM] no. 126300) or, more commonly, as part of the lymphedema-distichiasis (LD) syndrome (OMIM no. 153400). More than 45 families with mutations in the FOXC2 gene and LD have been described. Both lymphedema and distichiasis are highly penetrant. Distichiasis without lymphedema is not commonly seen.

METHODS

We examined three generations of a family (N = nine members) with hereditary distichiasis but without lymphedema or other features of LD syndrome. The FOXC2 gene was polymerase chain reaction--amplified from genomic DNA from all family members and examined for mutations.

RESULTS

Clinical examination showed distichiasis of all four lids in two affected family members across two generations. There were no other consistent ophthalmologic abnormalities in the family. A cytosine-to-adenine transversion was identified in DNA from affected study participants at nucleotide position 1076, which would be predicted to cause truncation of the protein at codon 359. This change was not observed in any of the nine unaffected family members participating.

CONCLUSIONS

This finding suggests that hereditary distichiasis and LD may not be separate genetic disorders but different phenotypic expressions of the same underlying disorder. Ophthalmologists should be aware that LD may present as distichiasis alone and counsel and refer their patients appropriately.

Structural and functional analyses of disease-causing missense mutations in the forkhead domain of FOXC1

Five missense mutations (P79L, P79T, I91S, I91T and R127H) within the forkhead DNA-binding domain of the FOXC1 transcription factor, identified in patients with Axenfeld-Rieger (AR) malformations, were studied to identify the effects of these mutations on FOXC1 structure and function. Molecular modeling and threading analyses predict that the I91S and T mutations may generate local disruptions to the structure of the forkhead domain while the R127H mutation alters the electrostatic charge of the DNA binding surface of the forkhead domain. The P79L and T mutations are not predicted to grossly perturb the structure of the forkhead domain. Biological analyses indicate that all of these missense mutations cause a range of FOXC1 perturbations, including nuclear localization defects, reduced or abolished DNA binding capacity, and a reduction in the transactivation capacity of FOXC1. These experiments extend our previous hypothesis that reduced transactivation of appropriate target genes by FOXC1, underlie AR malformations mapping to human chromosome 6p25. Importantly, these results can also be applied to predict the consequences of the molecular effects of mutations of other FOX genes that have analogous missense mutations, including FOXP2, FOXE3 and FOXC2.

Loss of eyes in zebrafish caused by mutation of chokh/rx3

The vertebrate eye forms by specification of the retina anlage and subsequent morphogenesis of the optic vesicles, from which the neural retina differentiates. chokh (chk) mutant zebrafish lack eyes from the earliest stages in development. Marker gene analysis indicates that retinal fate is specified normally, but optic vesicle evagination and neuronal differentiation are blocked. We show that the chk gene encodes the homeodomain-containing transcription factor, Rx3. Loss of Rx3 function in another teleost,medaka, has also been shown to result in an eyeless phenotype. The medaka rx3 locus can fully rescue the zebrafish mutant phenotype. We provide evidence that the regulation of rx3 is evolutionarily conserved, whereas the downstream cascade contains significant differences in gene regulation. Thus, these mutations in orthologous genes allow us to study the evolution of vertebrate eye development at the molecular level.

Anaesthesia for a child with Walker-Warburg syndrome

Walker-Warburg syndrome (WWS) is a rare lethal autosomal recessive disorder manifested by characteristic central nervous system and eye malformations. We have not come across reports of general anaesthesia in a child with WWS in the English literature. We report a case of general anaesthesia in a 12-month-old male child with WWS. The child also had bilateral cleft lip, cleft palate, urogenital malformation and hydronephrosis. Despite many potential anaesthesia concerns, anaesthesia was uneventful in this child.

[Hereditary foveal hypoplasia - clinical differentiation]

BACKGROUND

In a family cataract, esotropia and foveal hypoplasia is dominantly transmitted.

PATIENTS AND METHOD

Besides the physical examination visual evoked potentials and PAX6 mutation analysis were performed on five of six affected persons and on two who were not.

RESULTS

A man of the first generation, deceased before this study, was known to have low vision. His two daughters and their children and grandchildren suffer from cataract, esotropia and foveal hypoplasia. In two cases accompanied by aniridia and atypical iris coloboma respectively. The best visual acuity is 0.5. The VEPs taken of three of the affected people were normal. The PAX6 mutation analysis demonstrated a T to A translocation in the Intron 8 at the position + 2 (= IVS8 + 2T --> A).

CONCLUSION

1) This study confirms that foveal hypoplasia in the so-called isolated form have a similar origin as in aniridia namely PAX6 mutation and that it is a symptom in all cases while the iris anomaly may be variable. 2) In contrast to this foveal hypoplasia in albinism may occur variably in a family while the asymmetry of VEP is a constant finding. 3) Therefore the VEP alone is helpful to differentiate clinically wether a foveal hypoplasia belongs to the albino or to the aniridia group.

[Influence of genotype on endoreduplication of giant chromosomes and expressivity of character eyeless in Drosophila melanogaster]

In Drosophila melanogaster lines LA (low activity), HA (high activity), and Oregon-R (wild type), the effect of genetic background on endoreplication in giant chromosomes of salivary glands, fecundity, and expression of mutation ey was studied. The degree of chromosome polyteny and the number of adult flies in saturated lines eyHA, eyBA, and eyOr were significantly higher than in the original lines. The degree of chromosome polyteny was correlated with fecundity. The expressivity of the ey character was shown to be far lower in lines eyLA, eyHA, and eyOr than in the original eyeless line. In the saturated lines, the eye facets were reduced to a similar degree. All the lines studied displayed clear-cut sexual distinctions in this parameter. In the eyHA line, the coefficients of variation for the degree of chromosome polyteny, fecundity, and expressivity of the ey mutation were much lower than in lines eyeless, eyLA, and eyOr.

RECOGNITION OF THE CLINICAL SIGNS AND SYMPTOMS OF JOUBERT SYNDROME

Joubert Syndrome is a rare, autosomal recessive disorder that affects the cerebellum and brain stem. It presents with a distinct respiratory pattern and profound tachypnea in the newborn period. This article provides an overview of the condition and discusses the embryologic origins of this syndrome. A focused history and systematic physical assessment provide a step-by-step guide to enhance the early recognition of clinical signs and symptoms of this disorder. A series of clinical photographs and a brief case report offer insight into the classic presentation of this uncommon disorder. The diagnosis of Joubert syndrome is confirmed with magnetic resonance imaging, which reveals a classic neuroradiologic finding, characterized as the molar tooth sign. A discussion of the range of developmental outcomes and complex multispecialty care and intensive support that these infants and their families require is also provided.

Identification of a Pax6-dependent epidermal growth factor family signaling source at the lateral edge of the embryonic cerebral cortex

In an emerging model, area patterning of the mammalian cerebral cortex is regulated in part by embryonic signaling centers. Two have been identified: an anterior telencephalic source of fibroblast growth factors and the cortical hem, a medial structure expressing winglessint (WNT) and bone morphogenetic proteins. We describe a third signaling source, positioned as a mirror image of the cortical hem, along the lateral margin of the cortical primordium. The cortical antihem is identified by gene expression for three epidermal growth factor (EGF) family members, Tgf(alpha), Neuregulin 1, and Neuregulin 3, as well as two other signaling molecules, Fgf7 and the secreted WNT antagonist Sfrp2. We find that the antihem is lost in mice homozygous for the Small eye (Pax6) mutation and suggest the loss of EGF signaling at least partially explains defects in cortical patterning and cell migration in Small eye mice.

Linkage mapping of the primary disease locus for collie eye anomaly

Collie eye anomaly (cea) is a hereditary ocular disorder affecting development of the choroid and sclera segregating in several breeds of dog, including rough, smooth, and Border collies and Australian shepherds. The disease is reminiscent of the choroidal hypoplasia phenotype observed in humans in conjunction with craniofacial or renal abnormalities. In dogs, however, the clinical phenotype can vary significantly; many dogs exhibit no obvious clinical consequences and retain apparently normal vision throughout life, while severely affected animals develop secondary retinal detachment, intraocular hemorrhage, and blindness. We report genetic studies establishing that the primary cea phenotype, choroidal hypoplasia, segregates as an autosomal recessive trait with nearly 100% penetrance. We further report linkage mapping of the primary cea locus to a 3.9-cM region of canine chromosome 37 (LOD = 22.17 at theta = 0.076), in a region corresponding to human chromosome 2q35. These results suggest the presence of a developmental regulatory gene important in ocular embryogenesis, with potential implications for other disorders of ocular vascularization.