Search

Histone H3 lysine 4 trimethylation (H3K4me3) is well known to occur in the promoter region of genes for transcription activation. However, when investigating the H3K4me3 profiles in the mouse cerebrum and testis, we discovered that H3K4me3 also has a significant enrichment at the 3′ end of actively transcribed (sense) genes, named as 3′-H3K4me3. 3′-H3K4me3 is associated with ∼15% of protein-coding genes in both tissues. In addition, we examined the transcriptional initiation signals including RNA polymerase II (RNAPII) binding sites and 5′-CAGE-tag that marks transcriptional start sites. Interestingly, we found that 3′-H3K4me3 is associated with the initiation of antisense transcription. Furthermore, 3′-H3K4me3 modification levels correlate positively with the antisense expression levels of the associated sense genes, implying that 3′-H3K4me3 is involved in the activation of antisense transcription. Taken together, our findings suggest that H3K4me3 may be involved in the regulation of antisense transcription that initiates from the 3′ end of sense genes. In addition, a positive correlation was also observed between the expression of antisense and the associated sense genes with 3′-H3K4me3 modification. More importantly, we observed the 3′-H3K4me3 enrichment among genes in human, fruitfly and Arabidopsis, and found that the sequences of 3′-H3K4me3-marked regions are highly conserved and essentially indistinguishable from known promoters in vertebrate. Therefore, we speculate that these 3′-H3K4me3-marked regions may serve as potential promoters for antisense transcription and 3′-H3K4me3 appear to be a universal epigenetic feature in eukaryotes. Our results provide a novel insight into the epigenetic roles of H3K4me3 and the regulatory mechanism of antisense transcription.

A microsatellite-enriched library of plateau pika (Ochotona curzoniae) was constructed according to the strong affinity between biotin and streptavidin. Firstly, genomic DNA was fragmented by ultrasonication, which is a major improvement over traditional methods. Linker-ligated DNA fragments were hybridized with biotinylated microsatellite probes, and then were subjected to streptavidin-coated magnetic beads. PCR amplification was performed to obtain double-stranded DNA fragments containing microsatellites. Ligation and transformation were carried out by using the pGEM-T Vector System I and Escherichia coli DH10B competent cells. Sequencing results showed that 80.2% of clones contained microsatellite repeat motif. Several modifications make this protocol time-efficient and technically easier than the traditional ones; particularly, composition and relative abundance of microsatellite repeats in plateau pika genome were truly represented through the optimized PCR conditions. This method has also been successfully applied to construct microsatellite-enriched genomic libraries of Chinese hamster (Cricetulus griseus) and small abalone [Haliotis diversicolor (Reeve)] with high rates of positive clones, demonstrating its feasibility and stability.