There are lots of ways sperm cells are different from other cell types, but a new PLoS Genetics paper focused on one way in particular, chromatin structure, in order to find out what those differences mean and where they come from.In most cells, DNA is packaged up into nucleosomes, but in sperm, nucleosomes are only found in a small fraction of the genome, in places like the start sites of genes with high CG base content.
Armed with careful analysis of previously published ChIP-seq and microarray data, the team of Tanya Vavouri and Ben Lehner from Universitat Pompeu Fabra in Spain, uncovered that the sites where nucleosomes are retained in sperm are mainly governed by the base composition of the human genome. Here are more details on what they learned:
- Retained nucleosomes in sperm correlate to areas with high GC base content. This holds true for both genic and non-genic regions.
- Transcription start sites, especially for universally expressed and developmental genes, often hold on to their nucleosomes.
- Regions with retained nucleosomes in sperm are likely to be protected from DNA methylation in the early embryo, suggesting a connection between this mechanism in the paternal genome and the establishment of gene regulation in the embryo.
Based on their results, the researchers propose that an important evolutionary role of base composition in mammalian genomes may be to keep sperm chromatin organized so gene regulation in the early embryo can go off without a hitch.
Get all your sperm chromatin facts straight at PLoS Genetics, April 2011.