Summary Mechanosensitive sensory hair cells are the linchpin of our senses of hearing and balance. The inability of the mammalian inner ear to regenerate lost hair cells is the major reason for the permanence of hearing loss and certain balance disorders. Here we present a stepwise guidance protocol starting with mouse embryonic stem (ES) and induced pluripotent stem (iPS) cells, which were directed toward becoming ectoderm capable of responding to otic-inducing growth factors. The resulting otic progenitor cells were subjected to varying differentiation conditions, one of which promoted the organization of the cells into epithelial clusters displaying hair cell-like cells with stereociliary bundles. Bundle-bearing cells in these clusters responded to mechanical stimulation with currents that were reminiscent of immature hair cell transduction currents.

Nonmammalian vertebrates regenerate lost sensory hair cells by means of asymmetric division of supporting cells. Inner ear or lateral line supporting cells in birds, amphibians, and fish consequently serve as bona fide stem cells resulting in high regenerative capacity of hair cell-bearing organs. Hair cell regeneration does not happen in the mammalian cochlea, but cells with proliferative capacity can be isolated from the neonatal cochlea. These cells have the ability to form clonal floating colonies, so-called spheres, when cultured in nonadherent conditions. We noticed that the sphere population derived from mouse cochlear sensory epithelium cells was heterogeneous, consisting of morphologically distinct sphere types, hereby classified as solid, transitional, and hollow. Cochlear sensory epithelium-derived stem/progenitor cells initially give rise to small solid spheres, which subsequently transition into hollow spheres, a change that is accompanied by epithelial differentiation of the majority of sphere cells. Only solid spheres, and to a lesser extent, transitional spheres, appeared to harbor self-renewing stem cells, whereas hollow spheres could not be consistently propagated. Solid spheres contained significantly more rapidly cycling Pax-2-expressing presumptive otic progenitor cells than hollow spheres. Islet-1, which becomes upregulated in nascent sensory patches, was also more abundant in solid than in hollow spheres. Likewise, hair cell-like cells, characterized by the expression of multiple hair cell markers, differentiated in significantly higher numbers in cell populations derived from solid spheres. We conclude that cochlear sensory epithelium cell populations initially give rise to small solid spheres that have self-renewing capacity before they subsequently convert into hollow spheres, a process that is accompanied by loss of stemness and reduced ability to spontaneously give rise to hair celllike cells. Solid spheres might, therefore, represent the most suitable sphere type for cell-based assays or animal model transplantation studies aimed at development of cell replacement therapies.

Zusammenfassung Hintergrund Die Corona-Krise beeinflusst nicht nur das professionelle Handeln, sondern auch die Lehre an den Universitäten. Schlagworte wie „E-Learning“ und „Digitalisierung“ suggerieren die Möglichkeit innovativer, ad hoc verfügbarer Lösungsansätze für die Lehre in der aktuellen COVID-19-Situation. Die aktuelle Umstellung auf digitale Lehre ist aber nicht primär durch eine didaktische Sinnhaftigkeit oder institutionelle Strategie, sondern durch äußere Notwendigkeit geprägt. Ziel der Arbeit Ziel der Arbeit war die Erfassung der Lehrsituation an nationalen Universitäts-HNO-Kliniken und akademischen Lehrkrankenhäusern zu Beginn des virtuellen Corona-Sommersemesters 2020. Material und Methode Ein eigens erstellter Fragebogen zur jeweiligen lokalen Situation, den örtlichen Rahmenbedingungen sowie zu bundesweiten Szenarien wurde an alle 39 nationalen Universitäts-HNO-Kliniken und 20 akademischen Lehrkrankenhäuser mit HNO-Hauptabteilung versandt. Ergebnisse Die ausgefüllten Fragebögen von 31 Universitätskliniken (UK) und 10 akademische Lehrkrankenhäuser (ALK) gingen in die Auswertung ein. Es zeigten sich offensichtliche Diskrepanzen zwischen verfügbaren Ressourcen und tatsächlich verfügbaren digitalisierten Lehrinhalten. Weitere Kritikpunkte offenbarten sich in Bezug auf die Kommunikation mit der Medizinischen Fakultät, die digitale Infrastruktur und insbesondere in der oftmals mangelnden Kollaboration mit den zentralen Supportstrukturen, wie Medien‑, Didaktik- und Rechenzentren. Schlussfolgerung Es gibt durchaus positive Beispiele für eine gelungene Überführung der Präsenzlehre in das ausschließlich virtuelle Sommersemester 2020 innerhalb der Universitäts-HNO-Kliniken. Mehrheitlich aber überwiegen kritische Einschätzungen der Lehrbeauftragten bzw. Ärztlichen Direktoren gegenüber der aktuellen Lehrsituation. Eine zeitkritische strategische Weiterentwicklung ist dringend erforderlich.

Abstract. In head and neck squamous cell carcinoma (HNSCC), aldehyde dehydrogenase 1 family, member A1 (ALDH1A1) and hyaluronan receptor cluster of differentiation 44 (CD44) are often used as cancer stem cell (CSC) markers. The aim of the present study was to examine the relevance of these proteins for HNSCC in general and for the identification of CSCs. Tumors from 48 patients with primary HNSCC were analyzed for the expression of ALDH1A1 and CD44. Additionally, the association of the proteins with the proliferation rate and epidermal growth factor receptor (EGFR) expression was analyzed. ALDH1A1 was expressed in 54.2% of the carcinoma samples while CD44 was expressed in 89.6% of the carcinoma samples. Most notably, these proteins were often not expressed exclusively in a subpopulation, but also in the majority of tumor cells (ALDH1A1: 30.8% of ALDH1A1 + tumors; CD44: 65.1% of CD44 + tumors). Furthermore, patients with ALDH1A1 + tumors exhibited worse survival rates. CD44 and EGFR expression patterns were overlapping within the tumors and the expression rates were significantly connected. Ki-67 + tumor cells often expressed CD44. ALDH1A1 and CD44 expression patterns only partly overlapped. Consequently, ALDH1A1 and CD44 play significant roles in carcinogenesis and tumor progression. Within the present study, CD44 appeared to interact with EGFR and was more often expressed in primary HNSCC than the marker ALDH1A1. However, ALDH1A1 was a better marker to define a subpopulation of tumor cells. Finally, neither ALDH1A1 nor CD44, alone or combined, were sufficient to determine the CSC population in HNSCC.