Deciphering The Histone Code Of Globin Gene Switching And Identification Of Transgene's Integration Site

Transcription is a complex process that relies on the collective action of genetic and epigenetic regulation. Eukaryotic gene expression can be viewed within a conceptual framework in which regulatory mechanisms are integrated at three hierarchical levels, i.e. the sequence level, the chromatin level and the nuclear level. Recent studies have revealed that chromatin, the organized packing of DNA in the eukaryotic nucleus, plays a pivotal role in the regulation of gene expression. In addition, with the completion of an increasing number of organisms' genome, comparative genome analyses reveal a surprising constancy that many genes are clustered on the chromosomes and the clustered genes are co-regulated. Therefore, a central issue in the post-genome era is to discern the underlying transcriptional co-regulation mechanism at large gene cluster level.The basic repeating of chromatin, the nucleosome, includes two copies of the four core histones, H2A, H2B, H3 and H4, wrapped by 146 bp of DNA. Numerous studies in the past few years have witnessed that histone posttranslational modifications, including acetylation, methylation, phosphorylation and ubiquitylation, play an important role in eukaryotic gene regulation. The number, variety, and interdependence of histone modifications led to the histone code hypothesis, which predicts that multiple histone modifications, acting in a combination or sequential fashion on one or multiple histone tails, specify unique downstream function. A wealth studies have shown that histone modifications are critical for transcriptional co-regulation. Thus, it is of fundamental importance to explore the function of histone modification in transcription co-regulation of gene cluster.The mammalian globin gene family, consisting of α- and β-globin gene clusters, is an excellent model for elucidating the relationship between chromatin structure and gene regulation. The expression of globin genes is characterized by 1) sequential expression of individual gene in each cluster, 2) erythroid-specific and developmental stage-specific expression, 3) balance between a-like and p-like globin chains. The human α-globin gene cluster includes an embryonic ζ gene and 2 fetal/adult α genes lying close to the telomere of the short arm of chromosome 16 (tel-ζ-α2-α1-cen). A single switch occurs as...