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.