Every sip of this morning’s brew was processed by cells that are only around a week old. By the end of next week, many of those cells will have completed their tasks, and a new group will be savoring the flat whites instead.
Taste buds are small clusters of cells formed like segments of an orange, nestled into the bumps and grooves of the tongue. An adult possesses between 2,000 and 4,000 of them, according to the InformedHealth.org guide from Germany’s Institute for Quality and Efficiency in Health Care. Each bud contains 10 to 50 sensory cells, which renew approximately once a week. Additional taste cells can be found at the back of the throat and even in the upper section of the food pipe.
None of this comes with a memo.
How the ten-day duration was initially determined
In 1965, two biologists at Florida State University aimed to track the shifts. They injected rats with thymidine, a key component a cell utilizes to replicate its DNA prior to dividing, labeled with a faint radioactive marker. Cells that divided soon after absorbed the marker and passed it to their offspring, revealing as dark spots once thin slices of tongue were covered in photographic emulsion and allowed to develop.
In the Journal of Cell Biology, the duo reported that new cells emerged in the lining surrounding each bud, subsequently drifting towards its center. An average cell lived around 250 hours, give or take 50, rounding to approximately ten days. Some expired much sooner, while others lasted considerably longer. This was all measured in rats.
Some taste cells outlast others
Does every cell in a bud clock out simultaneously? A University of Miami team examined this with mice, as described in a paper published in PLOS One in 2013, categorizing the cells by type before starting the timer.
Type II cells, which possess the receptors for sweet, bitter, and savory (umami) flavors, had a half-life of eight days. Half-life refers to the duration it takes for half of a cohort to vanish, meaning that within just over a week, half of the receptor cells from any particular batch had disappeared. Type III cells, the most nerve-like types in the bud, were not in a rush, boasting a half-life of 22 days.
This constitutes a single study focusing on one area at the back of the tongue, thus the exact figures pertain only to that context. It aligns with the pattern observed by the Florida State pair decades earlier, and it reinterprets ten days as an average smoothed across varied lifespans.
Where the replacement cells originate
“Taste tissue regenerates continuously throughout the lifespan in mammals.” This statement opens the plain-language summary of a 2014 paper in PNAS from the Monell Chemical Senses Center, which sought to identify the source of all those new recruits.
The authors isolated individual stem cells from mouse taste tissue, distinguishing them by a surface protein termed Lgr5 (or its close relative Lgr6), which marks adult stem cells in several tissues. Cultured in a dish, a single one of these cells could proliferate into a small three-dimensional clump known as an organoid. Those clumps encompassed all the mature taste cell types, the cells reacted to taste chemicals, and they managed all of it without any nerve connection.
This capacity for renewal is uncommon among the body’s sensing cells. As a taste biology lab at the University of Colorado Anschutz Medical Campus notes, the light-sensing rods and cones in the eye and the hair cells of the inner ear lack this ability. Wear those out, and no replacements are forthcoming.
What occurs when the renewal ceases
Basal cell carcinoma, a prevalent skin cancer, can be treated with drugs that inhibit a growth signal known as Hedgehog, a chemical message that assists developing cells in determining their identity. Many patients receiving these medications report significant taste disturbances, prompting researchers at the University of Michigan to administer one of them, sonidegib, to mice and observe the aftermath, as described in PNAS in 2017.
The precursor cells that nourish each bud were disrupted from their regular cycle of dividing and maturing, leading to the disappearance of the buds. Nerve responses to taste were eliminated, while touch and cold sensitivities persisted. Once the drug was discontinued, the buds regenerated, and taste signals resumed.
It is a result observed in mice, yet it aligns well with reports of patients regaining taste after completing treatment.
Taste may feel like one of the most established aspects of an individual, as fixed as an accent. A decades-long aversion to coriander has been preserved by taste cells that have been replaced hundreds of times since the discord began.