Ocular abnormalities in Largemyd and Largevls mice, spontaneous models for muscle, eye, and brain diseases

Here we demonstrate previously unreported ocular defects in mice homozygous for a new allele of the Large gene, veils, and for Large(myd) mice. Clinically, vitreal fibroplasia and retinal vessel tortuosity and fluorescein leakage are observed. These vascular defects may be due to the extreme disorganization of the astrocytic template on which endothelial cells migrate in the retina. Abnormal electroretinograms recorded from Large(vls) or Large(myd) mice are accompanied by disorganization of the outer plexiform layer (OPL) with a dramatic reduction in the number of synaptic complexes. In both mutants, the internal limiting membrane (ILM) is disrupted with ectopic cells in the vitreous. Interestingly, while all components of the dystrophin glycoprotein complex are present at reduced levels in the OPL, they were absent in the ILM of affected mice. Finally, hypoglycosylation of alpha-dystroglycan previously implicated in muscle and brain defects is also observed in the retina and may contribute to the ocular abnormalities.

Mutations in rugose promote cell type-specific apoptosis in the Drosophila eye

RUGOSE (RG): encodes an A kinase anchor protein and was isolated as a genetic interactor of the Notch and epidermal growth factor receptor (EGFR) pathways during eye development in Drosophila. rg mutants display a small, rough eye phenotype primarily caused by the loss of cone cells. Here we show that the basis of this phenotype is cell type-specific apoptosis rather than transformation and hence can be rescued by reduction of proapoptotic signals. Moreover, a nearly complete rescue is observed by an increased Notch signal suggesting an antiapoptotic function of Notch in this developmental context. Cone cell loss in rg mutants is accompanied by enhanced Jun N-terminal kinase activity and, concomitantly, by a reduction of EGFR signalling activity. Together, these findings support the idea that rg plays an important role in the integration of different signals required for the exact regulation of cone cell development and survival.

Clinical and Molecular Characterization of a Family With Autosomal Recessive Cornea Plana

BACKGROUND

Autosomal recessive cornea plana is characterized by a flattened corneal surface associated with hyperopia and various anterior segment abnormalities. Mutations have been detected in the keratocan gene (KERA), a member of the small leucine-rich proteoglycan family.

OBJECTIVE

To clinically and molecularly characterize a consanguineous family of Hispanic origin in which 3 individuals are affected with cornea plana.

METHODS

Clinical ophthalmic examination, including corneal topography and axial eye length measurement, was performed on 7 family members. Molecular analysis of KERA was performed on DNA from each family member who had been examined.

RESULTS

All 3 affected individuals showed extreme flattening of the cornea (< 36 diopters [D]), normal axial eye lengths, and hyperopia greater than 6.25 D (spherical equivalent). Anterior segment abnormalities included scleralization of the cornea and central iris strands to the corneal endothelium. Affected individuals were homozygous for a novel mutation in KERA. The sequence change was found in exon 2, which results in an asparagine to aspartic acid change at codon 131. This amino acid change occurs within a highly conserved leucine-rich repeat of keratocan.

CONCLUSIONS

The cause of disease in this family is likely to be a mutation in exon 2 of KERA. Other mutations in KERA known to cause cornea plana also fall within the region encoding the leucine-rich repeat motifs and are predicted to affect the tertiary structure of the protein.

CLINICAL RELEVANCE

This is the first report of the identification of a mutation within KERA in a family of Hispanic origin with autosomal recessive cornea plana. Although the vast majority of cases of cornea plana are in individuals of Finnish descent, this report demonstrates the occurrence of the disease in other populations.

Neural and eye-specific defects associated with loss of the imitation switch (ISWI) chromatin remodeler in Xenopus laevis

Imitation Switch (ISWI) is a member of the SWI2/SNF2 superfamily of ATP-dependent chromatin remodelers, which regulate transcription and maintain chromatin structure by mobilizing nucleosomes using the energy of ATP. Four distinct ISWI complexes have been identified in Xenopus oocytes. The developmental role of Xenopus ISWI, however, has not previously been investigated in vivo. Here we report the tissue specificity, developmental expression, and requirement of ISWI for development of Xenopus embryos. Whole mount in situ hybridization shows ISWI localized in the lateral sides of the neural plate, brain, eye, and in later stages, the spinal cord. Injection of antisense ISWI RNA, morpholino oligonucleotides or dominant-negative ISWI mutant mRNA into fertilized eggs inhibits gastrulation and neural fold closure. Genes involved in neural patterning and development, such as BMP4 and Sonic hedgehog (Shh), are misregulated in the absence of functional ISWI, and ISWI binds to the BMP4 gene in vivo. Developmental and transcriptional defects caused by dominant-negative ISWI are rescued by co-injection of wild-type ISWI mRNA. Inhibition of ISWI function results in aberrant eye development and the formation of cataracts. These data suggest a critical role for ISWI chromatin remodeling complexes in neural development, including eye differentiation, in the Xenopus laevis embryo.

Novel mutations in BCOR in three patients with oculo-facio-cardio-dental syndrome, but none in Lenz microphthalmia syndrome

Oculo-facio-cardio-dental (OFCD) syndrome is a rare X-linked dominant condition with male lethality characterized by microphthalmia, congenital cataracts, facial dysmorphic features, congenital heart defects, and dental anomalies. Mutations in BCOR (BCL6 co-repressor) located in Xp11.4 have been described to cause OFCD syndrome. Lenz microphthalmia syndrome is inherited in an X-linked recessive pattern comprising microphthalmia/anophthalmia, mental retardation, malformed ears, digital, skeletal, and urogenital anomalies (synonym: microphthalmia with associated anomalies (MAA)). One locus for MAA has been mapped to Xq27-q28. Nonetheless, linkage and subsequent mutation analysis revealed a single missense mutation (p.P85L) in BCOR in a large family with presumed Lenz microphthalmia syndrome (MAA2). We describe novel mutations in BCOR in three patients with OFCD syndrome, two small deletions (c.2488_2489delAG and c.3286delG) and a submicroscopic deletion of about 60 kb encompassing at least BCOR exons 2-15. No BCOR mutation was detected in eight patients with Lenz microphthalmia syndrome. Our data confirm that BCOR is the causative gene for OFCD syndrome; however, the failure to identify any mutation in patients with Lenz microphthalmia syndrome together with the oligosymptomatic phenotype in the reported MAA2 patients suggest that BCOR is not the major gene for this syndrome.

CRYBB1 mutation associated with congenital cataract and microcornea

PURPOSE

The molecular characterization of a UK family with an autosomal dominant congenital cataract associated with microcornea is reported.

METHODS

Family history and clinical data were recorded. This phenotype was linked to a 7.6 cM region of chromosome 22q11.2-q12.2, spanning the beta-crystallin gene cluster (ZMax of 3.91 for marker D22S1114 at theta=0). Candidate genes were PCR amplified and screened for mutations on both strands using direct sequencing.

RESULTS

Sequencing of the coding regions and flanking intronic sequences of CRYBB2 and CRYBB1 showed the presence of a novel, heterozygous X253R change in exon 6 of CRYBB1. SSCP analysis confirmed that this sequence change segregated with the disease phenotype in all available family members and was not found in 109 ethnically matched controls.

CONCLUSIONS

X253R is predicted to elongate the COOH-terminal extension of the protein and would be expected to disrupt beta-crystallin interactions. This is the first documented involvement of CRYBB1 in ocular development beyond cataractogenesis.

Two cases of lacrimal gland agenesis in the same family — clinicoradiologic findings and management

BACKGROUND

Lacrimal gland agenesis is extremely rare. This condition is occasionally associated with salivary gland agenesis and abnormalities in the lacrimal drainage system, particularly occlusions of the lacrimal puncta and canaliculi. The detailed presentation of clinicoradiologic findings and treatment modality has not been previously reported.

METHODS

A 6-year-old boy was presented to our department complaining of severe foreign-body sensations in both eyes. Punctate epithelial erosions and mucous filaments were noted in both eyes. His tear break-up time (TBUT) was less than 1 second, and a Schirmer's test (both eyes) detected less than 1 mm of wetting in 5 minutes. His mother had similar complaints dating back to childhood.

RESULTS

Orbital computed tomography (CT) scan and magnetic resonance imaging (MRI) revealed the absence of both lacrimal glands and all major salivary glands. After the insertion of a lacrimal punctal plug, punctate epithelial erosions and mucous filaments decreased remarkably within 2 weeks. MRI scans of the patient's mother confirmed the absence of both lacrimal glands and salivary glands. She had been using artificial tears for a long time.

INTERPRETATION

The absence of lacrimal glands can be confirmed by clinicoradiologic findings, and the punctal plug may be an effective tool for the treatment of patients who retain a patent lacrimal drainage system.

Novel Rap1 dominant-negative mutants interfere selectively with C3G and Epac

Rap1 is a Ras-related GTPase that is principally involved in integrin- and E-cadherin-mediated adhesion. Rap1 is transiently activated in response to many incoming signals via a large family of guanine nucleotide exchange factors (GEFs). The lack of potent Rap1 dominant-negative mutants has limited our ability to decipher Rap1-dependent pathways; we have therefore developed a procedure to generate such mutants consisting in the oligonucleotide-mediated mutagenesis of residues 14-19, selection of mutants presenting an enhanced interaction with Epac2 by yeast two-hybrid screening and counter-screening for mutants still interacting with Rap effectors. In detail analysis of their interaction capacity with various Rap-GEFs in the yeast two-hybrid system revealed that mutants of residues 15 and 16 interacted with Epacs, C3G and CalDAG-GEFI, whereas mutants of position 17 had selectively lost their ability to bind CalDAG-GEFI as well as, for some, C3G. In cellular models where Rap1 is activated via endogenous GEFs, the Rap1[S17A] mutant inhibits both the cAMP-Epac and EGF-C3G pathways, whereas Rap1[G15D] selectively interferes with the latter. Finally, Rap1[S17A] is able to act as a bona fide dominant-negative mutant in vivo since it phenocopies the eye-reducing and lethal effects of D-Rap1 deficiency in Drosophila, effects that are overcome by the overexpression of D-Epac or D-Rap1.

Drosophila Vps16A is required for trafficking to lysosomes and biogenesis of pigment granules

Mutations that disrupt trafficking to lysosomes and lysosome-related organelles cause multiple diseases, including Hermansky-Pudlak syndrome. The Drosophila eye is a model system for analyzing such mutations. The eye-color genes carnation and deep orange encode two subunits of the Vps-C protein complex required for endosomal trafficking and pigment-granule biogenesis. Here we demonstrate that dVps16A (CG8454) encodes another Vps-C subunit. Biochemical experiments revealed a specific interaction between the dVps16A C-terminus and the Sec1/Munc18 homolog Carnation but not its closest homolog, dVps33B. Instead, dVps33B interacted with a related protein, dVps16B (CG18112). Deep orange bound both Vps16 homologs. Like a deep orange null mutation, eye-specific RNAi-induced knockdown of dVps16A inhibited lysosomal delivery of internalized ligands and interfered with biogenesis of pigment granules. Ubiquitous knockdown of dVps16A was lethal. Together, these findings demonstrate that Drosophila Vps16A is essential for lysosomal trafficking. Furthermore, metazoans have two types of Vps-C complexes with non-redundant functions.

Distinct capacities of individual E2Fs to induce cell cycle re-entry in postmitotic lens fiber cells of transgenic mice

PURPOSE

Inactivation of the retinoblastoma gene in human retinoblasts or mouse lens fiber cells causes inappropriate cell cycle entry, presumably as a consequence of elevated activity of the E2F transcription factors. Although E2Fs are known to be critical regulators of the cell cycle, it is still unclear whether family members E2F3a, E2F4 or E2F5 are individually capable of inducing cell cycle entry in vivo. In this study, we designed experiments to test whether lens-specific expression of these E2F family members would induce postmitotic fiber cells to re-enter the cell cycle.

METHODS

Transgenic mice were generated by microinjection of constructs that contained E2F cDNAs (E2F3a, E2F4 or E2F5) linked to the mouse lens-specific alphaA-crystallin promoter. The mice were characterized by histology, in situ hybridization, immunohistochemistry, BrdU incorporation, TUNEL assay and Western blots.

RESULTS

E2F3a expression was sufficient to induce cell cycle entry in lens fiber cells. Cell cycle re-entry was accompanied by apoptotic cell death resulting in microphthalmia. E2F4 expression stimulated a modest level of cell cycle re-entry, but the transgenic lenses remained normal in size and did not show significant apoptosis. Transgenic mice expressing E2F5 did not show lens defects. In both the E2F3a and E2F4 transgenic lenses, cyclin A2 and cyclin B1 expression were upregulated. Phosphorylated histone H3, a marker for mitosis, was detected in the E2F3a fiber cells. Western blots showed that both p53 and p73alpha were upregulated in the E2F3a lenses. However, expression of p21, a well-known p53 target gene, was not activated, suggesting that p73alpha might be responsible for inducing apoptosis and blocking unregulated proliferation in lens cells overexpressing E2F3a.

CONCLUSIONS

E2F3a and E2F4, but not E2F5, function to induce cell cycle entry, although E2F4 has more modest activity. E2F3a may induce cell death primarily through activation of p73alpha.

Conditional alleles for activation and inactivation of the mouse Rx homeobox gene

The Rx homeobox gene is a transcriptional regulator indispensable for development of the eye and ventral forebrain. Rx-null homozygotes lack optic pits, which are the earliest ocular structures. To study the roles Rx may play at various stages of eye and brain development, we generated an allelic series at the Rx locus. The targeted allele, Rx(neo), is a severely hypomorphic or null allele. This Rx(neo) allele is converted via FLP-mediated recombination to the Rx(flox) allele, which is phenotypically identical to the wildtype allele. Cre-mediated conversion of Rx(flox) generates the RxDelta2 allele, which, when homozygous, results in an Rx-null phenotype that includes perinatal lethality, anophthalmia, and anterior neural and craniofacial defects. Mice carrying these alleles allow both Cre-mediated inactivation and FLP-mediated activation of Rx gene activity on a conditional basis and will be useful in examining Rx function at different developmental stages and in distinct tissue environments.

Bax-like protein Drob-1 protects neurons from expanded polyglutamine-induced toxicity in Drosophila

Bcl-2 family proteins regulate cell death through the mitochondrial apoptotic pathway. Here, we show that the Drosophila Bax-like Bcl-2 family protein Drob-1 maintains mitochondrial function to protect cells from neurodegeneration. A pan-neuronal knockdown of Drob-1 results in lower locomotor activity and a shorter lifespan in adult flies. Either the RNAi-mediated downregulation of Drob-1 or overexpression of Drob-1 antagonist Buffy strongly enhances the polyglutamine-induced accumulation of ubiquitinated proteins and subsequent neurodegeneration. Furthermore, ectopic expression of Drob-1 suppresses the neurodegeneration and premature death of flies caused by expanded polyglutamine. Drob-1 knockdown decreases cellular ATP levels, and enhances respiratory inhibitor-induced mitochondrial defects such as loss of membrane potential (Deltapsim), morphological abnormalities, and reductions in activities of complex I+III and complex II+III, as well as cell death. Taken together, these results suggest that Drob-1 is essential for neuronal cell function, and that Drob-1 protects neurons from expanded polyglutamine-mediated neurodegeneration through the regulation of mitochondrial homeostasis.

Pathological aggression in "fierce" mice corrected by human nuclear receptor 2E1

"Fierce" mice, homozygous for the deletion of nuclear receptor 2E1 (NR2E1), show abnormal brain-eye development and pathological aggression. To evaluate functional equivalency between mouse and human NR2E1, we generated mice transgenic for a genomic clone spanning the human NR2E1 locus and bred these animals to fierce mice deleted for the corresponding mouse gene. In fierce mutants carrying human NR2E1, structural brain defects were eliminated and eye abnormalities ameliorated. Excitingly, behavior in these "rescue" mice was indistinguishable from controls. Because no artificial promoter was used to drive transgene expression, promoter and regulatory elements within the human NR2E1 clone are functional in mouse. Normal behavior in rescue animals suggests that mechanisms underlying the behavioral abnormalities in fierce mice may also be conserved in humans. Our data support the hypothesis that variation at NR2E1 may contribute to human behavioral disorders. Use of this rescue paradigm with other genes will permit the direct evaluation of human genes hypothesized to play a causal role in psychiatric disease but for which evidence is lacking or equivocal.

Persistent hyperplastic primary vitreous in association with neurofibromatosis 2

We describe a father and son with persistent hyperplastic primary vitreous occurring in association with neurofibromatosis 2. This report demonstrates rare vertical transmission compatible with autosomal dominant inheritance and the uncommon association of the autosomal dominant systemic disorder neurofibromatosis 2.

Anterior megalophthalmos in a family with 3 female siblings

This report describes different modes of management in 3 sisters with anterior megalophthalmos. We report our management of the anterior megalophthalmos and a new technique of anterior chamber intraocular lens implantation, which was used in 1 case.

Familial aplasia of the inferior rectus muscles

PURPOSE

We describe inferior rectus aplasia in three members of a family. No family member showed signs of craniofacial dysostosis syndromes or neurofibromatosis.

PATIENTS AND FINDINGS

A woman with abnormal head posture, right exotropia, and right hypotropia presented to our clinic. She mentioned that her two children had similar problems. A provisional diagnosis of ocular fibrosis or atypical Duane syndrome was made and she underwent surgery. During surgery, the inferior rectus muscle could not be identified in either eye. Subsequently, her children were examined and orbital magnetic resonance imaging (MRI) was performed for all family members. MRI confirmed bilateral absence of the inferior rectus muscles in the mother and unilateral absence with atrophic and fibrotic contralateral inferior rectus muscles in the children.

CONCLUSION

This is the first report in the literature of a family with aplastic inferior rectus muscles with no signs of craniosynostosis or neurofibromatosis.

Genetic dissection of Pax6 dosage requirements in the developing mouse eye

Haploinsufficiency of the transcription factor Pax6/PAX6 has been implicated in a number of congenital eye disorders in humans and mice, such as aniridia and Small-eye, which affect the development and function of the lens, cornea, anterior eye segment and neuroretina. However, the widespread distribution of Pax6/PAX6 protein within the developing and adult eye preclude the identification and direct study of the ocular tissues affected by a reduction in Pax6/PAX6 dosage. Here, we employed Cre/loxP-mediated inactivation of a single Pax6 allele in either the lens/cornea or the distal optic cup to dissect the tissue-specific sensitivity to Pax6 haploinsufficiency. Exclusive inactivation of a single Pax6 allele in the lens recapitulates the Small-eye lens and corneal defects, while only mildly affects iris morphology in a non-cell-autonomous fashion. Conversely, selective inactivation of a single Pax6 allele in the distal optic cup revealed primarily cell-autonomous dosage requirements for proper iris differentiation, with no affects on either lens or corneal morphology. Pax6 dosage within the distal optic cup is found here to influence the number of progenitors destined for the anterior ocular structures, the timing of iris muscle-cell differentiation and iris stroma development. Taken together, we genetically dissected the complex mouse Small-eye phenotype, thereby pinpointing the underlying Pax6/PAX6 haploinsufficiency to autonomous dosage requirements within the developing iris and lens/cornea tissues.

The v-ATPase V0 subunit a1 is required for a late step in synaptic vesicle exocytosis in Drosophila

The V(0) complex forms the proteolipid pore of an ATPase that acidifies vesicles. In addition, an independent function in membrane fusion has been proposed largely based on yeast vacuolar fusion experiments. We have isolated mutations in the largest V(0) component vha100-1 in flies in an unbiased genetic screen for synaptic malfunction. The protein is only required in neurons, colocalizes with markers for synaptic vesicles as well as active zones, and interacts with t-SNAREs. Loss of vha100-1 leads to vesicle accumulation in synaptic terminals, suggesting a deficit in release. The amplitude of spontaneous release events and release with hypertonic stimulation indicate normal levels of neurotransmitter loading, yet mutant embryos display severe defects in evoked synaptic transmission and FM1-43 uptake. Our data suggest that Vha100-1 functions downstream of SNAREs in synaptic vesicle fusion.

ZD6474 suppresses oncogenic RET isoforms in a Drosophila model for type 2 multiple endocrine neoplasia syndromes and papillary thyroid carcinoma

Patients with hereditary medullary thyroid carcinoma (MTC) associated with multiple endocrine neoplasia (MEN) types 2A and 2B and familial MTC (FMTC) have mutations in the RET proto-oncogene. Approximately 40 percent of patients with papillary thyroid carcinoma (PTC) typically have either intrachromosomal or extrachromosomal rearrangements that join the promoter and NH(2)-terminal domains of unrelated genes to the COOH-terminal fragment of RET. The RET point mutations associated with MEN2A, MEN2B, or FMTC, or the chromosomal breakpoints and translocations associated with PTC, typically activate the RET receptor tyrosine kinase (RTK). RET kinase inhibitors are likely to be beneficial for patients with hereditary MTC, where currently there is no effective chemotherapy or radiation therapy. Recently, the low molecular weight tyrosine kinase inhibitor ZD6474 was found to block the enzymatic activity of RET-derived oncoproteins in cultured cell lines. We have developed a Drosophila model for MEN2A and MEN2B diseases by targeting oncogenic forms of RET to the developing Drosophila eye. Here we show that, when fed orally, ZD6474 suppressed RET-mediated phenotypes within the context of this in vivo model. Importantly, ZD6474 showed high efficacy and very low toxicity. This compound failed to significantly suppress an activated form of another RTK, the Drosophila epidermal growth factor receptor, nor did it suppress the activity of downstream components of the RET/Ras pathway. Our results support the view that targeting chemical kinase inhibitors such as ZD6474 to tissues with oncogenic forms of RET is a useful treatment strategy for RET-dependent carcinomas.

Genetic screens for enhancers of brahma reveal functional interactions between the BRM chromatin-remodeling complex and the delta-notch signal transduction pathway in Drosophila

The Drosophila trithorax group gene brahma (brm) encodes the ATPase subunit of a 2-MDa chromatin-remodeling complex. brm was identified in a screen for transcriptional activators of homeotic genes and subsequently shown to play a global role in transcription by RNA polymerase II. To gain insight into the targeting, function, and regulation of the BRM complex, we screened for mutations that genetically interact with a dominant-negative allele of brm (brm(K804R)). We first screened for dominant mutations that are lethal in combination with a brm(K804R) transgene under control of the brm promoter. In a distinct but related screen, we identified dominant mutations that modify eye defects resulting from expression of brm(K804R) in the eye-antennal imaginal disc. Mutations in three classes of genes were identified in our screens: genes encoding subunits of the BRM complex (brm, moira, and osa), other proteins directly involved in transcription (zerknullt and RpII140), and signaling molecules (Delta and vein). Expression of brm(K804R) in the adult sense organ precursor lineage causes phenotypes similar to those resulting from impaired Delta-Notch signaling. Our results suggest that signaling pathways may regulate the transcription of target genes by regulating the activity of the BRM complex.

Functional analysis of NBC1 mutants associated with proximal renal tubular acidosis and ocular abnormalities

Mutations in the Na+-HCO3- co-transporter (NBC1) cause permanent proximal renal tubular acidosis (pRTA) with ocular abnormalities. However, little has been known about the relationship between the degree of NBC1 inactivation and the severity of pRTA. This study identified three new homozygous mutations (T485S, A799V, and R881C) in the common coding regions of NBC1. Functional analysis of these new as well as the known mutants (R298S and R510H) in Xenopus oocytes revealed a considerable variation in their electrogenic activities. Whereas the activities of R298S, A799V, and R881C were 15 to 40% of the wild-type (WT) activity, T485S and R510H, as a result of poor surface expression, showed almost no activities. However, T485S, like R510H, had the transport activity corresponding to approximately 50% of the WT activity in ECV304 cells, indicating that surface expression of T485S and R510H varies between the different in vitro cell systems. Electrophysiologic analysis showed that WT, R298S, and R881C all function with 2HCO3- to 1Na+ stoichiometry and have similar extracellular Na+ affinity, indicating that reduction in Na+ affinity cannot explain the inactivation of R298S and R881C. These results, together with the presence of nonfunctional mutants (Q29X and DeltaA) in other patients, suggest that at least approximately 50% reduction of NBC1 activity would be required to cause severe pRTA.