Denize Atan

Bhlhb5 and Prdm8 form a repressor complex involved in neuronal circuit assembly

Although transcription factors that repress gene expression play critical roles in nervous system development, their mechanism of action remains to be understood. Here, we report that the Olig-related transcription factor Bhlhb5 (also known as Bhlhe22) forms a repressor complex with the PR/SET domain protein, Prdm8. We find that Bhlhb5 binds to sequence-specific DNA elements and then recruits Prdm8, which mediates the repression of target genes. This interaction is critical for repressor function since mice lacking either Bhlhb5 or Prdm8 have strikingly similar cellular and behavioral phenotypes, including axonal mistargeting by neurons of the dorsal telencephalon and abnormal itch-like behavior. We provide evidence that Cadherin-11 functions as target of the Prdm8/Bhlhb5 repressor complex that must be repressed for proper neural circuit formation to occur. These findings suggest that Prdm8 is an obligate partner of Bhlhb5, forming a repressor complex that directs neural circuit assembly in part through the precise regulation of Cadherin-11.

Cytokine polymorphism in noninfectious uveitis.

PURPOSE Noninfectious uveitis is a sight-threatening immune-mediated intraocular inflammatory disorder. The inheritance of uveitis in multiplex families and its association with known monogenic and polygenic immunologic disorders suggests that common genetic variants underlie susceptibility to uveitis as well as to other immunologic disorders. TNFA and IL10 are strong candidate genes, given the influence of these cytokines on inflammation, immune tolerance, and apoptosis. METHODS The role of 12 polymorphisms spanning the TNFA and IL10 genomic regions was investigated in 192 uveitis patients and 92 population control subjects from four regional centers in the United Kingdom and Republic of Ireland. RESULTS The results demonstrate that uveitis is associated with three haplotype-tagging SNPs (htSNPs) in the IL10 gene: htSNP2 (rs6703630), htSNP5 (rs2222202), and htSNP6 (rs3024490). IL10htSNP2AG/htSNP5TC was the most significantly associated haplotype (P = 0.00085), whereas the LTA+252AA/TNFhtSNP2GG haplotype was protective (P = 0.00031). Furthermore, subgroup analysis showed that the frequency of the TNFd4 allele was higher in patients with nonremitting ocular disease and/or those requiring higher levels of maintenance immunosuppression. Although these associations lost significance after Bonferroni correction, they infer a relationship that may be validated by a larger study. CONCLUSIONS Since these variants are implicated in the susceptibility and severity of several immunologic disorders, the results support the hypothesis that common genetic determinants influence shared mechanisms of autoimmunity.

Punctate inner choroidopathy and multifocal choroiditis with panuveitis share haplotypic associations with IL10 and TNF Loci

PURPOSE The white-dot syndromes are a heterogenous group of chorioretinal disorders that have many common clinical features. Whether these disorders represent distinct clinical entities or different manifestations of the same disease warrants further interrogation. Two white-dot syndromes were investigated, with closely overlapping phenotypes--multifocal choroiditis with panuveitis (MFCPU) and punctate inner choroidopathy (PIC)--for differences in clinical course and genotype frequency at IL10 and TNF loci, known to be associated with noninfectious uveitis. METHODS Twelve polymorphisms were genotyped, spanning the TNFA and IL10 genomic regions, in 61 patients with MFCPU or PIC and 92 population controls from the United Kingdom and Republic of Ireland. RESULTS There were clear differences in clinical course between patients with MFCPU and PIC which had prognostic significance. However, both patient groups demonstrated similar associations with the IL10 haplotype, IL10htSNP2(-2849)AX/htSNP5(+434)TC and negative associations with the TNF haplotype, LTA+252A/TNFhtSNP1(-308)G/TNFhtSNP2(-238)G/TNFhtSNP3(+488)A/TNFd3. CONCLUSIONS Despite clear differences in clinical course and outcome, MFCPU and PIC may still represent two manifestations of the same disease, given their similar genetic associations with IL10 and TNF loci, which are known to be associated with noninfectious uveitis and autoimmunity, in general. Definitive proof will necessitate genomewide sequence analysis. However, the data also support the notion that epigenetic factors have a strong effect on clinical phenotype.

Transcription factor PRDM8 is required for rod bipolar and type 2 OFF-cone bipolar cell survival and amacrine subtype identity

Significance Knowledge of the molecules that guide retinal interneuron formation is incomplete. We showed that PRDI-BF1 and RIZ homology domain containing 8 (PRDM8) is required for the development of rod bipolar cells and OFF-cone bipolar subtypes as well as amacrine cell identity. Although bipolar cells were specified in Prdm8-null mice, rod bipolar cell differentiation was impaired, leading to their death and near absence from adult retina. This defect disrupts postphotoreceptor signal transduction, as shown by nonprogressive b-wave deficits in electroretinograms. Our findings suggest PRDM8 as a candidate gene for human congenital stationary night blindness. They also establish PRDM8 as a component of the regulatory network governing bipolar cell development and amacrine cell diversity, aiding efforts to generate these essential interneurons in vitro. Retinal bipolar (BP) cells mediate the earliest steps in image processing in the visual system, but the genetic pathways that regulate their development and function are incompletely known. We identified PRDI-BF1 and RIZ homology domain containing 8 (PRDM8) as a highly conserved transcription factor that is abundantly expressed in mouse retina. During development and in maturity, PRDM8 is expressed strongly in BP cells and a fraction of amacrine and ganglion cells. To determine whether Prdm8 is essential to BP cell development or physiology, we targeted the gene in mice. Prdm8EGFP/EGFP mice showed nonprogressive b-wave deficits on electroretinograms, consistent with compromised BP cell function or circuitry resembling the incomplete form of human congenital stationary night blindness (CSNB). BP cell specification was normal in Prdm8EGFP/EGFP retina as determined by VSX2+ cell numbers and retinal morphology at postnatal day 6. BP subtype differentiation was impaired, however, as indicated by absent or diminished expression of BP subtype-specific markers, including the putative PRDM8 regulatory target PKCα (Prkca) and its protein. By adulthood, rod bipolar (RB) and type 2 OFF-cone bipolar (CB) cells were nearly absent from Prdm8-null mice. Although no change was detected in total amacrine cell (AC) numbers, increased PRKCA+ and cholinergic ACs and decreased GABAergic ACs were seen, suggesting an alteration in amacrine subtype identity. These findings establish that PRDM8 is required for RB and type 2 OFF-CB cell survival and amacrine subtype identity, and they present PRDM8 as a candidate gene for human CSNB.

Sorsby fundus dystrophy presenting with choroidal neovascularisation showing good response to steroid treatment

Sorsby fundus dystrophy (SFD) is a dominantly inherited macular dystrophy in which bilateral central visual loss occurs in the fifth decade of life.1 Duke-Elder and Perkins described it as pseudo-inflammatory macular dystrophy.2 It is now known to be caused by mutations in exon 5 of the gene for TIMP3 ,3 tissue inhibitor of metalloproteinases-3. The disorder has variable expressivity and signs vary depending on age at review, but common fundus characteristics include diffuse fine yellow-white deposits, macular choroidal neovascularistion (CNV), and delayed choroidal filling and retinal pigment epithelial (RPE) mottling on fluorescein angiography (FFA). Later stages include atrophy of the macula and periphery.1,2 Punctate inner choroidopathy (PIC) is characterised by multiple yellow opacities at the level of the inner choroid of the posterior pole and mid periphery without other evidence of inflammation. CNV is a frequent complication which responds to steroid treatment.4 We describe a patient who presented with clinical signs consistent with PIC complicated by bilateral CNV. The CNV was treated over a period of six years using either oral or subTenon steroids with improvement in vision. She was subsequently found to have SFD. A 36 year old woman presented with a two month history of difficulty reading with the left eye. Past ocular and medical history were unremarkable except for mild myopia (−2.00 dioptres). On examination, visual acuities …

New insights into the genetic component of non-infectious uveitis through an Immunochip strategy

Background Large-scale genetic studies have reported several loci associated with specific disorders involving uveitis. Our aim was to identify genetic risk factors that might predispose to uveitis per se, independent of the clinical diagnosis, by performing a dense genotyping of immune-related loci. Methods 613 cases and 3693 unaffected controls from three European case/control sets were genotyped using the Immunochip array. Only patients with non-infectious non-anterior uveitis and without systemic features were selected. To perform a more comprehensive analysis of the human leucocyte antigen (HLA) region, SNPs, classical alleles and polymorphic amino acid variants were obtained via imputation. A meta-analysis combining the three case/control sets was conducted by the inverse variance method. Results The highest peak belonged to the HLA region. A more detailed analysis of this signal evidenced a strong association between the classical allele HLA-A*2902 and birdshot chorioretinopathy (p=3.21E-35, OR=50.95). An omnibus test yielded HLA-A 62 and 63 as relevant amino acid positions for this disease. In patients with intermediate and posterior uveitis, the strongest associations belonged to the rs7197 polymorphism, within HLA-DRA (p=2.07E-11, OR=1.99), and the HLA-DR15 haplotype (DRB1*1501: p=1.16E-10, OR=2.08; DQA1*0102: p=4.37E-09, OR=1.77; DQB1*0602: p=7.26E-10, OR=2.02). Outside the HLA region, the MAP4K4/IL1R2 locus reached statistical significance (rs7608679: p=8.38E-07, OR=1.42). Suggestive associations were found at five other loci. Conclusions We have further interrogated the association between the HLA region and non-infectious non-anterior uveitis. In addition, we have identified a new non-HLA susceptibility factor and proposed additional risk loci with putative roles in this complex condition.

Education and myopia: assessing the direction of causality by mendelian randomisation

Abstract Objectives To determine whether more years spent in education is a causal risk factor for myopia, or whether myopia is a causal risk factor for more years in education. Design Bidirectional, two sample mendelian randomisation study. Setting Publically available genetic data from two consortiums applied to a large, independent population cohort. Genetic variants used as proxies for myopia and years of education were derived from two large genome wide association studies: 23andMe and Social Science Genetic Association Consortium (SSGAC), respectively. Participants 67 798 men and women from England, Scotland, and Wales in the UK Biobank cohort with available information for years of completed education and refractive error. Main outcome measures Mendelian randomisation analyses were performed in two directions: the first exposure was the genetic predisposition to myopia, measured with 44 genetic variants strongly associated with myopia in 23andMe, and the outcome was years in education; and the second exposure was the genetic predisposition to higher levels of education, measured with 69 genetic variants from SSGAC, and the outcome was refractive error. Results Conventional regression analyses of the observational data suggested that every additional year of education was associated with a more myopic refractive error of −0.18 dioptres/y (95% confidence interval −0.19 to −0.17; P<2e-16). Mendelian randomisation analyses suggested the true causal effect was even stronger: −0.27 dioptres/y (−0.37 to −0.17; P=4e-8). By contrast, there was little evidence to suggest myopia affected education (years in education per dioptre of refractive error −0.008 y/dioptre, 95% confidence interval −0.041 to 0.025, P=0.6). Thus, the cumulative effect of more years in education on refractive error means that a university graduate from the United Kingdom with 17 years of education would, on average, be at least −1 dioptre more myopic than someone who left school at age 16 (with 12 years of education). Myopia of this magnitude would be sufficient to necessitate the use of glasses for driving. Sensitivity analyses showed minimal evidence for genetic confounding that could have biased the causal effect estimates. Conclusions This study shows that exposure to more years in education contributes to the rising prevalence of myopia. Increasing the length of time spent in education may inadvertently increase the prevalence of myopia and potential future visual disability.

Unremitting sympathetic ophthalmia associated with homozygous interleukin-10-1082A single nucleotide polymorphism

Sympathetic ophthalmia (SO) is a rare,1 bilateral, granulatomatous panuveitis following injury to one eye. Inflammation develops after the relative immune privilege of the eye is compromised, causing sensitisation to previously sequestrated uveoretinal antigens.2 Although potentially blinding, the outcome may be favourable if aggressive systemic immunosuppression is initiated early.1 3 While certain genetic variants of the human leucocyte antigen (HLA) genes influence susceptibility to SO,4 5 single nucleotide polymorphisms (SNPs) in cytokine genes influence severity of disease.7 We report a case of SO who progressively deteriorated despite early immunosuppression. She was later found to be homozygous for the interleukin-10 (IL-10)-1082A SNP. A 48-year-old woman presented with a 2-week history of blurred vision and floaters in her left eye, 9 weeks after a right ruptured globe repair. …

A comparative analysis of rod bipolar cell transcriptomes identifies novel genes implicated in night vision

In the mammalian retina, rods and a specialised rod-driven signalling pathway mediate visual responses under scotopic (dim light) conditions. As rods primarily signal to rod bipolar cells (RBCs) under scoptic conditions, disorders that affect rod or RBC function are often associated with impaired night vision. To identify novel genes expressed by RBCs and, therefore, likely to be involved in night vision, we took advantage of the adult Bhlhe23−/− mouse retina (that lacks RBCs) to derive the RBC transcriptome. We found that genes expressed by adult RBCs are mainly involved in synaptic structure and signalling, whereas genes that influence RBC development are also involved in the cell cycle and transcription/translation. By comparing our data with other published retinal and bipolar cell transcriptomes (where we identify RBCs by the presence of Prkca and/or Pcp2 transcripts), we have derived a consensus for the adult RBC transcriptome. These findings ought to facilitate further research into physiological mechanisms underlying mammalian night vision as well as proposing candidate genes for patients with inherited causes of night blindness.

Immunohistochemical Phenotyping of Mouse Amacrine Cell Subtypes

The retina shares its embryological origin with the central nervous system (CNS), so the neural circuitry of the retina has long been considered to be a relatively simple model of the neural networks in the brain, sharing similar morphologies, neurotransmitters, and receptors. Amacrine cells are, by far, the largest group of inhibitory neurons in the retina that also have the most diverse range of phenotypes of any retinal neuron. Here, I describe an approach, using immunolabeling of cryosections, to identify different subclasses of amacrine cell in the mouse retina.