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Distal enhancer-insulator module of GDF6 is essential for cochlear formation
Mohammad Faraz Zafeer, Clemer Abad, Havva Ortabozkoyun, Memoona Ramzan, Guney Bademci, Maria C. Robayo, Duygu Duman, Rolen M. Quadros, Shengru Guo, Juan I. Young, Anthony J. Griswold, Channabasavaiah B. Gurumurthy, Derek M. Dykxhoorn, Katherina Walz, Mustafa Tekin
Mohammad Faraz Zafeer, Clemer Abad, Havva Ortabozkoyun, Memoona Ramzan, Guney Bademci, Maria C. Robayo, Duygu Duman, Rolen M. Quadros, Shengru Guo, Juan I. Young, Anthony J. Griswold, Channabasavaiah B. Gurumurthy, Derek M. Dykxhoorn, Katherina Walz, Mustafa Tekin
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Research Article Development Genetics

Distal enhancer-insulator module of GDF6 is essential for cochlear formation

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Abstract

Several genes guide inner ear development, and mutations in these genes can cause malformations that result in congenital hearing loss. However, the contribution of noncoding regulatory elements remains largely unclear. This study investigates the function of distal enhancer elements in the transcriptional regulation of GDF6, a gene implicated in cochlear development. Using mouse models with targeted deletions, human inner ear organoids, and CRISPR interference (CRISPRi), we identified a downstream regulatory interval harboring a developmental enhancer required to maintain GDF6 expression during otic epithelial maturation and cochlear morphogenesis. Deletion of this regulatory region or targeting of CRISPRi-based repressors to these regions resulted in decreased GDF6 expression, failure of otic-epithelium development, and prevention of hair cell–like differentiation, reflecting cochlear aplasia observed in patients with corresponding genomic deletions. These findings highlight the contribution of long-range regulatory elements to auditory development and illustrate how their disruption contributes to human deafness.

Authors

Mohammad Faraz Zafeer, Clemer Abad, Havva Ortabozkoyun, Memoona Ramzan, Guney Bademci, Maria C. Robayo, Duygu Duman, Rolen M. Quadros, Shengru Guo, Juan I. Young, Anthony J. Griswold, Channabasavaiah B. Gurumurthy, Derek M. Dykxhoorn, Katherina Walz, Mustafa Tekin

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Figure 2

A putative GDF6 enhancer lesion impairs otic organoid development and hair cell formation in patient-derived IEOs.

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A putative GDF6 enhancer lesion impairs otic organoid development and ha...
(A) Brightfield images of inner ear organoids (IEOs) differentiated from control (CD-2) and proband (166-101) iPSCs at days –2, 3, 8, 12, and 15. (B) Representative confocal immunofluorescence images (n = 3, 20× magnification; scale: 50 µm) of control and proband IEOs across differentiation: day 5-ECAD, pSMAD1/5/9, Hoechst (blue); day 8-TFAP2A/AP2, CDH1/ECAD, DAPI (blue); day 8-CDH1/ECAD, GDF6, DAPI (blue); day 12-CDH1/ECAD, PAX2, DAPI (blue); day 20-CDH1/ECAD, PAX8, DAPI (blue). Proband IEOs show reduced and disorganized expression of otic epithelial and prosensory markers compared with controls. (C) qRT-PCR analysis of GDF6 mRNA in control (CD2) and proband (166-101) IEOs at days 8, 12, and 15, normalized to HPRT1. Proband cultures show significantly reduced GDF6 expression at all 3 time points (**P < 0.01 at day 8; ***P < 0.001 at days 12 and 15). Statistical comparisons were performed by 1-way ANOVA followed by Tukey’s post hoc test for multiple comparisons (n = 3). (D) qRT-PCR analysis of CDH1 (E-cadherin) mRNA expression at day 8, normalized to HPRT1, showing modestly reduced expression in proband IEOs (*P < 0.05; n = 3). (E) qRT-PCR analysis of CDH1 mRNA expression at day 12, normalized to HPRT1, showing markedly reduced expression in proband IEOs (**P < 0.01; n = 3). (F) qRT-PCR analysis of PAX2 mRNA expression at day 15, normalized to HPRT1, showing significantly reduced prosensory marker expression in proband IEOs (**P < 0.01; n = 3). Statistical comparisons in panels D–F were performed by unpaired 2-tailed Student’s t test. (G) Representative confocal immunocytochemistry (n = 3; 40× magnification; scale bar: 20 µm) of day 55 IEO sections stained for SOX2 (red, supporting cells), MYO7A (green, hair cells), phalloidin (yellow, F-actin), and DAPI (blue, nuclei). Control IEOs contain robust MYO7A-positive hair cells with organized apical F-actin and SOX2-positive supporting cells, whereas proband IEOs lack MYO7A-positive cells and display reduced, disorganized SOX2 immunoreactivity.

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