Researchers maintained human brain organoids in laboratory culture for five years, demonstrating that the tissue models intrinsically record the passage of developmental time, according to a study published in Nature. The work, also reported by New Scientist, tracked cellular and epigenetic progression across 110 organoids comprising 424,720 cells.
Profiling data showed that organoids aged from 15 days to two months mapped transcriptionally to first-trimester human fetal brains, while organoids cultured between nine months and five years shifted toward late prenatal and postnatal profiles. Whole-genome bisulfite sequencing across nine timepoints revealed that DNA methylation closely tracked chronological culture time. Predicted methylation ages calculated with the Horvath pan-tissue clock and a human cortex-specific clock correlated with culture duration at coefficients between 0.88 and 0.90.
Chimeric experiments revealed that progenitor cells retain a memory of their developmental age. When researchers combined neural progenitors of different ages into chimeric organoids, older progenitors produced late neuronal fates directly, bypassing earlier developmental progeny.
The team introduced an activity permissive medium, known as APM, to improve long-term neuronal survival compared to standard CDM4 conditions. APM supplemented BrainPhys medium with GlutaMax starting at day 70 in vitro. At nine months, APM-treated organoids contained significantly higher numbers of SATB2-positive callosal projection neurons and active SATB2-positive FOS-positive cells.
Electron microscopy tests confirmed that 52 percent of synapses in one-year-old APM organoids were located on dendritic spines, compared to 25 percent in CDM4 controls. Expansion microscopy at seven months showed increased total neurite length, branch extension, and higher maximum Strahler arborization numbers in APM-cultured neurons.
