Tag Archives: X chromosome inactivation

The RNA world strikes again (it never stopped)

Jpx is a long (over 200 nucleotides) nonCoding (for protein that is) RNA (e.g. a lncRNA).  It is an example of the RNA world from which we (presumably) sprang. One of its function is to control another RNA, and a fairly important one at that — namely Xist, which inactivates one of a woman’s two X chromosomes.  The jpx gene is just 10 kiloBases away from that of Xist. Jpx turns on the transcription of Xist which then goes and coats the X chromosome from which it is transcribed, shutting off most of its genes.

One of the mechanisms by which Jpx turns on Xist production is by binding to a protein called CTCF.  CTCF sits on the promoter of the Xist gene until Jpx binds to it displacing CTCF from the promoter.

CTCF is a much better known actor, and along with cohesin is thought to be responsible for the formation of chromosome loops, and the establishment of TADs (topologically associated domains) which are basically loops of chromosomes containing about a million nucleotides with an average of 8 protein coding genes which are coordinately expressed as a result.

That’s fairly impressive.  What happens when you knock out the jpx gene.  [ Cell vol. 184 pp. 6157 – 6173 ’21 ] did just this and all Hell broke loose.  Jpx keeps CTCF from binding promotors, and without jpx thousands of chromosome loops are replaced by others, with downregulation of some 700 protein coding genes.

Again, the RNA world is like some legacy software (think DOS) underlying the latest stuff (think Windows), forgotten but not gone.