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Atonal homolog 7 (ATOH7) loss-of-function mutations in predominant bilateral optic nerve hypoplasia


Atac, David; Koller, Samuel; Hanson, James V M; Feil, Silke; Tiwari, Amit; Bahr, Angela; Baehr, Luzy; Magyar, István; Kottke, Raimund; Gerth-Kahlert, Christina; Berger, Wolfgang (2020). Atonal homolog 7 (ATOH7) loss-of-function mutations in predominant bilateral optic nerve hypoplasia. Human Molecular Genetics, 29(1):132-148.

Abstract

Optic nerve hypoplasia (ONH) is a congenital optic nerve abnormality caused by underdevelopment of retinal ganglion cells (RGCs). Despite being a rare disease, ONH is the most common optic disc anomaly in ophthalmological practice. So far, mutations in several genes have been identified as causative, however many cases of ONH remain without a molecular explanation. The early transcription factor atonal basic-helix-loop-helix (bHLH) transcription factor 7 (ATOH7) is expressed in retinal progenitor cells and has a crucial role in RGC development. Previous studies have identified several mutations in the ATOH7 locus in cases of eye developmental diseases such as nonsyndromic congenital retinal nonattachment and persistent hyperplasia of the primary vitreous. Here we present two siblings with a phenotype predominated by bilateral ONH, with additional features of foveal hypoplasia and distinct vascular abnormalities, where whole-exome sequencing identified two compound heterozygous missense mutations affecting a conserved amino acid residue within the bHLH domain of ATOH7 (NM_145178.3:c.175G>A; p.(Ala59Thr) and c.176C>T; p.(Ala59Val)). ATOH7 expression constructs with patient single nucleotide variants were cloned for functional characterization. Protein analyses revealed decreased protein amounts and significantly enhanced degradation in the presence of E47, a putative bHLH dimerization partner. Protein interaction assays revealed decreased heterodimerization and DNA-binding of ATOH7 variants, resulting in total loss of transcriptional activation of luciferase reporter gene expression. These findings strongly support pathogenicity of the two ATOH7 mutations, one of which is novel. Additionally, this report highlights the possible impact of altered ATOH7 dimerization on protein stability and function.

Abstract

Optic nerve hypoplasia (ONH) is a congenital optic nerve abnormality caused by underdevelopment of retinal ganglion cells (RGCs). Despite being a rare disease, ONH is the most common optic disc anomaly in ophthalmological practice. So far, mutations in several genes have been identified as causative, however many cases of ONH remain without a molecular explanation. The early transcription factor atonal basic-helix-loop-helix (bHLH) transcription factor 7 (ATOH7) is expressed in retinal progenitor cells and has a crucial role in RGC development. Previous studies have identified several mutations in the ATOH7 locus in cases of eye developmental diseases such as nonsyndromic congenital retinal nonattachment and persistent hyperplasia of the primary vitreous. Here we present two siblings with a phenotype predominated by bilateral ONH, with additional features of foveal hypoplasia and distinct vascular abnormalities, where whole-exome sequencing identified two compound heterozygous missense mutations affecting a conserved amino acid residue within the bHLH domain of ATOH7 (NM_145178.3:c.175G>A; p.(Ala59Thr) and c.176C>T; p.(Ala59Val)). ATOH7 expression constructs with patient single nucleotide variants were cloned for functional characterization. Protein analyses revealed decreased protein amounts and significantly enhanced degradation in the presence of E47, a putative bHLH dimerization partner. Protein interaction assays revealed decreased heterodimerization and DNA-binding of ATOH7 variants, resulting in total loss of transcriptional activation of luciferase reporter gene expression. These findings strongly support pathogenicity of the two ATOH7 mutations, one of which is novel. Additionally, this report highlights the possible impact of altered ATOH7 dimerization on protein stability and function.

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Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > University Hospital Zurich > Ophthalmology Clinic
04 Faculty of Medicine > University Children's Hospital Zurich > Medical Clinic
04 Faculty of Medicine > Institute of Medical Molecular Genetics
Dewey Decimal Classification:570 Life sciences; biology
610 Medicine & health
Scopus Subject Areas:Life Sciences > Molecular Biology
Life Sciences > Genetics
Health Sciences > Genetics (clinical)
Language:English
Date:1 January 2020
Deposited On:07 Jan 2020 10:55
Last Modified:27 Dec 2020 08:16
Publisher:Oxford University Press
ISSN:0964-6906
OA Status:Green
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1093/hmg/ddz268
PubMed ID:31696227

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