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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 4

CRISPRi perturbation of a GDF6 regulatory region impairs otic epithelial organization and hair cell differentiation in IEOs.

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CRISPRi perturbation of a GDF6 regulatory region impairs otic epithelial...
(A) Representative confocal immunofluorescence images (n = 3; 20× magnification; scale bar: 50 µm) of day 8 IEOs derived from parental CD2dCas9, CD2dCas9-CTCF (targeting the putative CTCF site), and CD2dCas9-CAN (targeting the candidate enhancer) lines, stained for DAPI (blue), SOX2 (orange), TFAP2A/AP2 (magenta), and CDH1/ECAD. (B) qRT-PCR analysis of GDF6 mRNA expression in IEOs at days 8, 12, and 15, normalized to HPRT1. Both CD2dCas9-CTCF and CD2dCas9-CAN lines show significantly reduced GDF6 expression compared with parental CD2dCas9 at all 3 time points (day 8: ***P < 0.001 for CTCF, **P < 0.01 for CAN; day 12: ***P < 0.001 for CTCF, *P < 0.05 for CAN; day 15: *P < 0.05 for CTCF, ***P < 0.001 for CAN). Data are presented as mean ± SEM from 3 biological replicates (each pooled from ~8 organoids) per sample. Statistical comparisons were performed by 1-way ANOVA followed by Tukey’s post hoc test for multiple comparisons. (C) Representative confocal immunocytochemistry of day 55 IEOs from CD2dCas9, CD2dCas9-CTCF, and CD2dCas9-CAN lines stained for DAPI (blue), SOX2, MYO7A (magenta), and ESPN. The top row shows whole-organoid overviews (n = 2; 20× magnification); the bottom row shows high-magnification views (n = 2; 40× magnification; scale bar: 50 µm) of the same samples.

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