Lab-grown “mini brains,” called brain organoids, kind of look like navy beans—and have very little in common with a functional human brain. These tiny clumps of neural tissue are grown from stem cells and mimic the earliest stages of brain development. Scientists typically culture organoids for just a few months, allowing them to study how the cells begin to grow and organize into more complex tissues.
But what happens if they let the tissues develop for longer? In a new study published today in Nature, researchers sustained brain organoids in the lab for years, dramatically extending the organoids’ longevity and opening new opportunities to investigate neural development and disease.
“There are parts of development and maturation of the human brain ... that we really don’t know very much about,” says Harvard University stem cell researcher Paola Arlotta, senior author of the new study. Hoping to replicate some of those little-understood developmental stages, she says, “we decided to push this and say, ‘Okay, let’s go way farther.’”
Arlotta and her team documented the organoids’ progress over five years before submitting their research. And then the team continued culturing some for two more years before ending the experiment. In a growing medium designed to support neuronal activity, the organoids maintained a diverse collection of brain cells while they underwent changes in gene activity, cell types and other features that mirrored those seen during normal human brain development. They also appeared to mark the passage of time, with their DNA accumulating chemical tags called methyl groups, which scientists often use to estimate a person’s biological age.
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