Generating high-fidelity cochlear organoids from human pluripotent stem cells

Mapping the developmental potential of mouse inner ear organoids at single-cell resolution

“…74, 75 Even so, at least one report has shown evidence of both vestibular and cochlear HC fates with only slight modifications to the original Koehler protocol 77 and modulations of HH and WNT signaling were deemed sufficient to tip the balance towards cochlear cell fates. 24 Using scRNA-seq, we profiled a total of 3,029 HCLCs and in an unbiased clustering approach we determined that a significant number of HCLCs acquired a transcriptional signature reminiscent of auditory HCs. It remains to be determined if those cells develop in designated cysts or organoids that exclusively give rise to auditory HCLCs or if they develop intermingled with their vestibular counter parts.…”

Inner Ear Organoids: Strengths and Limitations

“…Careful electrophysiological characterization of the murine IEOs determined that hair cells have specific vestibular features [ 11 ]. More recently, using a modified guidance protocol, it has been demonstrated that it is possible to promote the differentiation of cochlear-like hair cells, with the bundle morphology, marker expression, and transcriptional identity of human fetal cochlear hair cells [ 12 ].…”

“…A recent set of papers has provided an in-depth characterization of human iPSC-derived IEOs and a first comparison with human inner ear embryonic and fetal samples [ 12 , 14 – 18 ]. By comparing single-cell profiling of IEOs, human fetal inner ear and adult vestibular epithelia, as well as by histological comparison, these studies established that in vitro differentiation follows similar timing and dynamics as in vivo.…”

“…Cells differentiated in IEOs for 50–70 days match marker expression and maturity of weeks 10–12 human development [ 14 , 17 ]. Further differentiation in culture until days 150–200 brings the maturity of the culture closer to weeks 18–20 of fetal inner ear development, when functionality starts [ 12 ]. These studies represent an important step forward for the field; however, more complete human inner ear embryonic/fetal/adult atlases are needed as a reference, in order for these types of studies to give a full picture of the differentiating sensory epithelia and ganglia during human development [ 19 , 20 ].…”

“…While sufficient for qualitative assessment, quantification biases can be introduced if not all sections are considered. Alternatively, one could use reporter lines to monitor the presence and quantify the number of selected cell types [ 12 , 38 ]. Live-fluorescence may be difficult to evaluate with image-based methods in large organoids due to light scattering but could facilitate quantification by alternative approaches, such as flow cytometry.…”