The time of appearance of the C. elegans let-7 microRNA is transcriptionally controlled utilizing a temporal regulatory element in its promoter.
Johnson, Steven M, Shin Yi Lin, and Frank J Slack. 2003. “The Time of Appearance of the C. Elegans Let-7 MicroRNA Is Transcriptionally Controlled Utilizing a Temporal Regulatory Element in Its Promoter.”. Developmental Biology 259 (2): 364-79.