In 1942 Conrad Waddington pictures a landscape of valleys. A cell rolls downhill along one valley into its final fate, and the landscape itself comes from something beyond the DNA sequence.
The Visitor looks down at the same landscape inside the cell.
A Second Code on One Molecule
- The same DNA sequence produces neurons, muscle cells, and immune cells. A second code of chemical marks on DNA and on histones sets which genes each cell can reach.
- The page sorts the second code into three roles. Writers add marks (DNMT, HAT, HMT). Readers interpret marks (MBD, PHD, bromodomain proteins). Erasers remove marks (TET, HDAC, KDM).
- The marks pass through cell division, respond to development and environment, and can be reversed.
- The page notes that CpG islands at gene promoters stay protected from methylation by a mechanism that reads the genetic sequence, so the two codes operate on one molecule in step with each other.
Waddington's landscape: each cell rolls down one valley into its fate. The site page carries the writer, reader, and eraser families.
Name the three roles in the epigenetic system and give one enzyme family for each.
Writers (DNMT, HAT, or HMT), readers (MBD, PHD, or bromodomain proteins), erasers (TET, HDAC, or KDM).
A second code written on top of the DNA lets one genome serve every cell type.
The Visitor lights node 02 and watches the link to Histones glow.
See the map