On p. 3924 of this article in the section `Mammary organoid culture', the concentrations of three constituents in the basal medium are incorrect. The correct concentrations are 10 μg/ml insulin, 5.5 μg/ml transferrin and 5 ng/ml sodium selenite.

In addition, the authors also wish to acknowledge Jimmie E. Fata for his suggestions regarding this assay.

The authors apologise to readers for these mistakes.

Development132, 3923-3933.