Defining Inner Ear Cell Type Specification at Single-Cell Resolution in a Model of Human Cranial Development

Kiaa1024L/Minar2 is essential for hearing by regulating cholesterol distribution in hair bundles

“…Our results with mutant zebrafish reveal that the hearing defects exist at the level of hair cells. This conclusion is consistent with the highly enriched expression of Kiaa1024L/Minar2 in the hair cells in the vertebrate inner ears, shown by our in situ hybridization results and our surveys of FACS and single cell RNA sequencing data (Barta et al, 2018;Elkon et al, 2015;Erickson & Nicolson, 2015;Liu et al, 2018;Steinhart et al, 2022). Outside the inner ear, Kiaa1024L/Minar2 is also expressed in various regions in the brain tissue, and a previous study showed loss of Minar2 in mice impairs motor function and reduces the number of tyrosine hydroxylase-positive neurons (Ho et al, 2020).…”

“…We surveyed available sequencing data (Barta et al, 2018;Elkon et al, 2015;Erickson & Nicolson, 2015;Liu et al, 2018) and found the transcripts of minar2 orthologs were highly enriched in the auditory hair cells of the mouse and the zebrafish (Figure 1-figure supplement 1B). In a human inner ear organoid model (Steinhart et al, 2022), MINAR2 is specifically expressed in differentiated hair cells, similar to known differentiated hair cell markers (Figure 1-figure supplement 1B). Consistent with these sequencing based data, in situ hybridization results confirmed minar2 was specifically expressed by the hair cells of the inner ears and the lateral line neuromasts in the developing zebrafish (Figure 1A).…”

“…In conclusion, our data provide evidence that cholesterol plays an essential role in the hair bundle, and Kiaa1024L/Minar2 regulates cholesterol distribution and homeostasis to ensure normal hearing. Because of the conserved requirement of Kiaa1024L/Minar2 gene orthologs for hearing in both mouse and zebrafish, and that the human ortholog MINAR2 is also spcifically expressed by the auditory hair hairs (Steinhart et al, 2022), it will be important to examine whether KIAA1024L/MINAR2 gene mutations may underline hearing abnormality in human. Further studies of Kiaa1024L/Minar2’s regulation of cholesterol distribution and homeostasis in the zebrafish and mammalian model will provide new insights into the biological process for the morphogenesis and physiology of hair bundles and hearing loss.…”

“…minar2 orthologs are highly expressed in the hair cells. Expression data were taken from published sources: mouse (Elkon et al, 2015;Liu et al, 2018), zebrafish (Barta et al, 2018;Elkon et al, 2015;Erickson & Nicolson, 2015), and human inner ear organoid (Steinhart et al, 2022) To study minar2 function in the zebrafish, we generated minar2 mutant alleles by CRISPR/Cas9 mediated mutagenesis. The mutation in the minar2 fs139 allele was a 5-bp deletion in exon 1, and in the minar2 fs140 allele was a 5-bp insertion in exon 1 (Figure 1figure supplement 1C).…”

“…(B) minar2 orthologs are highly expressed in the hair cells. Expression data were taken from published sources: mouse (Elkon et al, 2015; Liu et al, 2018), zebrafish (Barta et al, 2018; Elkon et al, 2015; Erickson & Nicolson, 2015), and human inner ear organoid (Steinhart et al, 2022). (C) Targeted disruption of the zebrafish minar2 gene by CRISPR/Cas9.…”