Increased cell-to-cell variation in gene expression in ageing mouse heart

Bahar et al. 2006.
Increased cell-to-cell variation in gene expression in ageing mouse heart. Nature 441, 1011–1014.

Bahar and colleagues isolated single cardiomyocytes from young and old mice and measured expression of a small panel of genes by single-cell qPCR (single-cell RNA-seq did not yet exist at scale).

The finding: cell-to-cell variation in expression was substantially higher in old hearts, even when mean expression was similar. They interpreted this as stochastic transcriptional noise accumulating with age, possibly from somatic DNA damage. It was the first clean demonstration that aging is a variance phenomenon, not just a mean-shift phenomenon. For cybernetic attractor decay, it is the original empirical anchor for computational drift.