Generation and Culture of Lingual Organoids Derived from Adult Mouse Taste Stem Cells

The sense of taste is mediated by taste buds on the tongue, which are composed of rapidly renewing taste receptor cells (TRCs). This continual turnover is ...

University of Colorado Anschutz Medical Campus

In mice, BDNF provided by the developing taste epithelium is required for gustatory neuron survival following target innervation. However, we find that expression of BDNF, as detected by BDNF-driven Î²-galactosidase, begins in the cranial ganglia before its expression in the central (hindbrain) or peripheral (taste papillae) targets of these sensory neurons, and before gustatory ganglion cells innervate either target. To test early BDNF function, we examined the ganglia of bdnf null mice before target innervation, and found that while initial neuron survival is unaltered, early neuron development is disrupted. In addition, fate mapping analysis in mice demonstrates that murine cranial ganglia arise from two embryonic populations, i.e., epibranchial placodes and neural crest, as has been described for these ganglia in non-mammalian vertebrates. Only placodal neurons produce BDNF, however, which indicates that prior to innervation, early ganglionic BDNF produced by placode-derived cells promotes gustatory neuron development.

Epibranchial placode-derived neurons produce BDNF required for early sensory neuron development.

Chez les souris, BDNF fournie par l&#39;&eacute;pith&eacute;lium de go&ucirc;t en d&eacute;veloppement est n&eacute;cessaire pour la survie de neurone gustative apr&egrave;s l&#39;innervation de la cible. Toutefois, on constate que l&#39;expression de BDNF, tel que d&eacute;tect&eacute; par ax&eacute;e sur le BDNF &beta;-galactosidase, commence dans les ganglions cr&acirc;niennes avant son expression dans la centrale (cerveau post&eacute;rieur) ou des cibles p&eacute;riph&eacute;riques (papilles du go&ucirc;t) de ces neurones sensoriels, et avant les cellules ganglionnaires gustative innervent une cible. Pour tester la fonction pr&eacute;coce de BDNF, nous avons examin&eacute; les ganglions de bdnf souris null avant l&#39;innervation de la cible et constat&eacute; que tandis que la survie du neurone initial est inchang&eacute;e, du d&eacute;veloppement de la neurone est perturb&eacute;. En outre, sort cartographie analyse chez la souris montre que les ganglions cr&acirc;niens murines proviennent de deux populations embryonnaires, c.-&agrave;-d. &eacute;pibranchial placodes et cr&ecirc;te neurale, comme cela a &eacute;t&eacute; d&eacute;crit pour ces ganglions chez les vert&eacute;br&eacute;s non mammif&egrave;res. Seulement placodaux neurones produisent BDNF, cependant, ce qui indique qu&#39;avant l&#39;innervation, d&eacute;but BDNF ganglionnaire produite par les cellules d&eacute;riv&eacute;es placode favorise le d&eacute;veloppement de neurone gustatifs.

&Eacute;pibranchial d&eacute;riv&eacute;s placode neurones produisent BDNF requis pour le d&eacute;veloppement des neurones sensoriels.

Nei topi, BDNF fornito da epitelio gusto in via di sviluppo &egrave; necessario per la sopravvivenza del neurone gustativo seguito innervazione di destinazione. Tuttavia, abbiamo trovato che espressione di BDNF, come rilevato da BDNF-driven &beta;-galattosidasi, comincia nei gangli cranici prima sua espressione nella centrale (hindbrain) o obiettivi periferico (papille gusto) di questi neuroni sensoriali, e prima che le cellule gangliari gustative innervano o destinazione. Per testare la funzione BDNF precoce, abbiamo esaminato i gangli di bdnf topi null prima di innervazione di destinazione e trovato che mentre la sopravvivenza neurone iniziale &egrave; inalterata, lo sviluppo precoce del neurone &egrave; perturbato. Inoltre, destino mappatura analisi nei topi dimostra che murini gangli cranici derivano da due popolazioni embrionale, cio&egrave;, epibranchial placodi e cresta neurale, come &egrave; stato descritto per questi gangli in vertebrati mammiferi. Solo placodal neuroni producono BDNF, tuttavia, che indica che prima di innervazione, primi BDNF ganglionica prodotta da cellule derivate da placode promuove lo sviluppo gustativo neurone.

Epibranchial derivate da placode neuroni producono BDNF necessaria per lo sviluppo precoce del neurone sensoriale.

En ratones, BDNF proporcionado por el epitelio de gusto en desarrollo es necesario para la supervivencia de la neurona gustativa siguiendo a inervaci&oacute;n de destino. Sin embargo, nos encontramos con que expresi&oacute;n de BDNF, detectada por basadas en BDNF &szlig;-galactosidasa, comienza en los ganglios craneales antes de su expresi&oacute;n en la central (cerebelo) u objetivos perif&eacute;rico (papilas del gusto) de estas neuronas sensoriales, y antes de c&eacute;lulas ganglionares gustativo inervan a cualquier destino. Para probar la funci&oacute;n temprana de BDNF, examinamos los ganglios de bdnf ratones null antes de inervaci&oacute;n del destino y encontr&oacute; que mientras que la supervivencia de la neurona inicial es inalterada, desarrollo temprano de la neurona se interrumpe. Adem&aacute;s, sino asignaci&oacute;n an&aacute;lisis en ratones demuestra que los ganglios craneales murinos surgen dos poblaciones embrionarias, es decir, epibranchial placodes y cresta neural, como se ha descrito para estos ganglios en los vertebrados no mam&iacute;feros. S&oacute;lo placodal las neuronas producen BDNF, sin embargo, que indica que antes de inervaci&oacute;n, BDNF ganglionar temprana producida por las c&eacute;lulas derivadas de placode promueve el desarrollo de la neurona gustativa.

Epibranchial derivados del placode neuronas producen BDNF necesario para el desarrollo temprano de la neurona sensorial.

Wnt/β-catenin signaling initiates taste papilla development in mouse embryos, however, its involvement in taste cell turnover in adult mice has not been explored. Here we used the BATGAL reporter mouse model, which carries an engineered allele in which the LacZ gene is expressed in the presence of activated β-catenin, to determine the responsiveness of adult taste bud cells to canonical Wnt signaling. Double immunostaining with markers of differentiated taste cells revealed that a subset of Type I, II, and III taste cells express β-galactosidase. Using in situ hybridization, we showed that β-catenin activates the transcription of the LacZ gene mainly in intragemmal basal cells that are immature taste cells, identified by their expression of Sonic Hedgehog (Shh). Finally, we showed that β-catenin activity is significantly reduced in taste buds of 25-week-old mice compared with 10-week-old animals. Our data suggest that Wnt/β-catenin signaling may influence taste cell turnover by regulating cell differentiation. Reduced canonical Wnt signaling in older mice could explain in part the loss of taste sensitivity with aging, implicating a possible deficiency in the rate of taste cell renewal. More investigations are now necessary to understand if and how Wnt signaling regulates adult taste cell turnover.

Taste bud cells of adult mice are responsive to Wnt/β-catenin signaling: implications for the renewal of mature taste cells.

Continuous taste bud cell renewal is essential to maintain taste function in adults; however, the molecular mechanisms that regulate taste cell turnover are unknown. Using inducible Cre-lox technology, we show that activation of β-catenin signaling in multipotent lingual epithelial progenitors outside of taste buds diverts daughter cells from a general epithelial to a taste bud fate. Moreover, while taste buds comprise 3 morphological types, β-catenin activation drives overproduction of primarily glial-like Type I taste cells in both anterior fungiform (FF) and posterior circumvallate (CV) taste buds, with a small increase in Type II receptor cells for sweet, bitter and umami, but does not alter Type III sour detector cells. Beta-catenin activation in post-mitotic taste bud precursors likewise regulates cell differentiation; forced activation of β-catenin in these Shh+ cells promotes Type I cell fate in both FF and CV taste buds, but likely does so non-cell autonomously. Our data are consistent with a model where β-catenin signaling levels within lingual epithelial progenitors dictate cell fate prior to or during entry of new cells into taste buds; high signaling induces Type I cells, intermediate levels drive Type II cell differentiation, while low levels may drive differentiation of Type III cells. 

β-Catenin Signaling Biases Multipotent Lingual Epithelial Progenitors to Differentiate and Acquire Specific Taste Cell Fates.

Taste stimuli are transduced by taste buds and transmitted to the brain via afferent gustatory fibers. Renewal of taste receptor cells from actively dividing progenitors is finely tuned to maintain taste sensitivity throughout life. We show that conditional β-catenin deletion in mouse taste progenitors leads to rapid depletion of progenitors and Shh+ precursors, which in turn causes taste bud loss, followed by loss of gustatory nerve fibers. In addition, our data suggest LEF1, TCF7 and Wnt3 are involved in a Wnt pathway regulatory feedback loop that controls taste cell renewal in the circumvallate papilla epithelium. Unexpectedly, taste bud decline is greater in the anterior tongue and palate than in the posterior tongue. Mutant mice with this regional pattern of taste bud loss were unable to discern sweet at any concentration, but could distinguish bitter stimuli, albeit with reduced sensitivity. Our findings are consistent with published reports wherein anterior taste buds have higher sweet sensitivity while posterior taste buds are better tuned to bitter, and suggest β-catenin plays a greater role in renewal of anterior versus posterior taste buds.

β-catenin is required for taste bud cell renewal and behavioral taste perception in adult mice.

Head and neck cancer patients receiving conventional repeated, low dose radiotherapy (fractionated IR) suffer from taste dysfunction that can persist for months and often years after treatment. To understand the mechanisms underlying functional taste loss, we established a fractionated IR mouse model to characterize how taste buds are affected. Following fractionated IR, we found as in our previous study using single dose IR, taste progenitor proliferation was reduced and progenitor cell number declined, leading to interruption in the supply of new taste receptor cells to taste buds. However, in contrast to a single dose of IR, we did not encounter increased progenitor cell death in response to fractionated IR. Instead, fractionated IR induced death of cells within taste buds. Overall, taste buds were smaller and fewer following fractionated IR, and contained fewer differentiated cells. In response to fractionated IR, expression of Wnt pathway genes, Ctnnb1, Tcf7, Lef1 and Lgr5 were reduced concomitantly with reduced progenitor proliferation. However, recovery of Wnt signaling post-IR lagged behind proliferative recovery. Overall, our data suggest carefully timed, local activation of Wnt/β-catenin signaling may mitigate radiation injury and/or speed recovery of taste cell renewal following fractionated IR.

Fractionated head and neck irradiation impacts taste progenitors, differentiated taste cells, and Wnt/β-catenin signaling in adult mice.

The main neurological manifestation of COVID-19 is loss of smell or taste. The high incidence of smell loss without significant rhinorrhea or nasal congestion suggests that SARS-CoV-2 targets the chemical senses through mechanisms distinct from those used by endemic coronaviruses or other common cold-causing agents. Here we review recently developed hypotheses about how SARS-CoV-2 might alter the cells and circuits involved in chemosensory processing and thereby change perception. Given our limited understanding of SARS-CoV-2 pathogenesis, we propose future experiments to elucidate disease mechanisms and highlight the relevance of this ongoing work to understanding how the virus might alter brain function more broadly.

COVID-19 and the Chemical Senses: Supporting Players Take Center Stage.

Since the early 20 th century, progress in cancer therapies has significantly improved disease prognosis. Nonetheless, cancer treatments are often associated with side effects that can negatively affect patient wellbeing and disrupt the course of treatment. Among the main side effects, taste impairment is associated with depression, malnutrition and morbid weight loss. Although relatively common, taste disruption associated with cancer therapies remains poorly understood. Here, we review the current knowledge related to the molecular mechanisms underlying taste maintenance and disruption in the context of cancer therapies.

Linda A. Barlow

Department of Cell and Developmental Biology and the Rocky Mountain Taste and Smell Center

University of Colorado Anschutz Medical Campus

Generation and Culture of Lingual Organoids Derived from Adult Mouse Taste Stem Cells

Linda A. Barlow

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Cell and Developmental Biology and the Rocky Mountain Taste and Smell Center

University of Colorado Anschutz Medical Campus

Generation and Culture of Lingual Organoids Derived from Adult Mouse Taste Stem Cells

Department of Cell and Developmental Biology and the Rocky Mountain Taste and Smell Center