'With his student, Jeff Richards, he found that addition of the hormone ecdysone could trigger a self-running process of sequential changes in the pattern of puffs. This led to the first proposal of the existence of cascades of gene regulation during development, which was presented at the 1973 Cold Spring Harbor Symposium'

https://www.sciencedirect.com/science/article/pii/S0960982223010722?via%3Dihub