# SA-β-Gal (Senescence-associated β-galactosidase)

SA-β-Gal (senescence-associated β-galactosidase) is an enzyme activity you can detect at pH 6.0. It reflects the swollen lysosomes and extra β-galactosidase (made by the GLB1 gene) found in senescent cells. Dimri and colleagues first described it in 1995. It became the most widely used single stain for spotting senescent cells, in tissue slices and in cell culture, because it is easy to detect. But it is not exclusive to senescent cells. It can also show up in resting (quiescent) cells, over-crowded cells, or cells under lysosomal stress. So it is best used alongside other markers (like p21, p16^INK4a, SASP components, and heterochromatin foci) to reliably identify senescence.

## Sources

- Dimri GP, Lee X, Basile G, et al.. (1995). A biomarker that identifies senescent human cells in culture and in aging skin in vivo. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.92.20.9363
- González-Gualda E, Baker AG, Fruk L, Muñoz-Espín D. (2021). A guide to assessing cellular senescence in vitro and in vivo. FEBS Journal. https://doi.org/10.1111/febs.15570

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