▶︎ CANCELED: Kroc Lecture
Transcriptional enhancers switch genes on and off in response to a variety of intrinsic and external cellular signals. Live imaging methods in Drosophila suggest that they regulate the frequency of transcriptional bursts, and can co-activate linked genes positioned in cis or in trans (transvection). Distal enhancers are brought into proximity with their target promoters by "tethering elements", but even upon activation the distances remain rather large, ~200-300 nm. These observations are consistent with emerging evidence for transcriptional condensates containing higher order associations of Pol II and other components of the pre-initiation complex.
In an effort to explore the evolutionary origins of novel cell types I will also present evidence that the tadpole of the proto-vertebrate, Ciona intestinalis, contains "rudiments" of key vertebrate innovations such as cranial placodes and neural crest. Comprehensive single-cell RNA sequencing assays identified ~15 different neuronal subtypes in the sensory vesicle (simple brain) of swimming tadpoles. Comparative analyses suggest that many of these neurons undergo subfunctionalization to produce diverse specialized neurons in vertebrates.