Some people dress up their pets in clothes so that they will look more like their human owners. Turns out, a similar thing happens in the nuclear transfer process to make stem cells. Jerome Jullien and colleagues in 2012 Nobel laureate John B. Gurdon’s lab (along with a number of other great researchers in France with great accents) report that a Xenopus oocyte will “dress up” the chromatin it gets from a transferred nucleus with its own oocyte histone H3.3. This is a necessary step for nuclear reprogramming.
The team wanted to know how nuclear reprogramming happens when they transfer a somatic cell nucleus into an oocyte, a step in the process of making pluripotent cells. H3.3 can make silent genes active after nuclear transfer, but the researchers wanted to find out more details about this process. Here’s some of what they learned:
- A lot of oocyte H3.3 versus H3.2 winds up on the transplanted chromatin.
- Once there, the H3.3 doesn’t turn over much.
- Silent genes get reactivated in the transplanted chromatin.
- H3.3 accumulates and reaches a plateau level on chromatin. Genes get reactivated during this time, though reactivation goes into overdrive after H3.3 incorporation reaches that plateau.
- H3.3 accumulation is DNA-replication independent, but needs transcription and the histone chaperone HIRA.
“This study demonstrates that the incorporation of histone H3.3 is an early and necessary step in the direct reprogramming of somatic cell nuclei by [an] oocyte,” they say.
For all the details, read the paper at Epigenetics & Chromatin, October 2012.