Transcriptional memory

Transcriptional memory is a biological phenomenon, initially discovered in yeast,^[1] during which cells primed with a particular cue show increased rates of gene expression after re-stimulation at a later time. This event was shown to take place: in yeast during growth in galactose^[1][2] and inositol starvation;^[3] plants during environmental stress;^[4][5][6] in mammalian cells during LPS^[7] and interferon^[8][9][10] induction. Prior work has shown that certain characteristics of chromatin may contribute to the poised transcriptional state allowing faster re-induction. These include: activity of specific transcription factors,^[11][12][13] retention of RNA polymerase II at the promoters of poised genes,^[9] activity of chromatin remodeling complexes,^[2] propagation of H3K4me2^[8][13] and H3K36me3^[10] histone modifications, occupancy of the H3.3 histone variant,^[10] as well as binding of nuclear pore components.^[9][14] Moreover, locally bound cohesin was shown to inhibit establishment of transcriptional memory in human cells during interferon gamma stimulation.^[15]

Principle of transcriptional memory. A pulse of an inducer (priming) results in expression of target genes, which subsides upon withdrawal. During a window of no induction (window of memory), some genes maintain a poised but transcriptionally silent state that results in a stronger gene activation upon a second challenge.