Fitting all that chromatin into a tiny package is no easy ordeal, especially when pristine nuclear architecture is so crucial to things like cancer prevention. In order to learn more about the chromatin packaging of mouse embryonic stem cells (ESCs) and sperm, a team from the University of Massachusetts Medical School laid out some high-resolution nucleosome and transcription factor (TF) blue prints. Here’s a quick sketch of the footprints that deep paired-end sequencing of lightly digested chromatin revealed:
- A genome-wide catalog of where nucleosomes and TFs like to bind in different chromatin states.
- Sperm histone retention primarily occurs in large gene-poor regions. It’s still not clear what those protoamines have against the intergenic areas.
- Only a small subset of sperm histone retention relates to promoters of developmental regulators.
- Mature sperm do seem to enjoy the company of the genomic insulator CTCF, which authors speculate may give sperm some much needed genomic organization upon histone depletion.
The team suggests that these findings represent a model where the sperm packaging state preferentially protects epigenetic silencing marks from removal at repeat elements, sets the groundwork for some detailed exploration into the chromatin architecture of differentiating cells, and shows a novel localization of histone retention in sperm that may be of great developmental importance. The researchers hope that advances in epigenome editing will soon allow them to target histone eviction or covalent modifications at loci of interest to “definitively determine the role for sperm histones in zygotic biology.”
Check out the maturation of the full chromatin package in Developmental Cell, July 2014