The importance of packing correctly
Many genes in mammals have C-phosphate-G (CpG) islands at the start of the gene and are promoters that begin transcription. These genes show differences in transcription, and researchers with the EVO-CHROMO (Sperm chromatin and the evolution of chromatin architecture at regulatory regions in animal genomes) project have investigated whether this is linked to chromatin, the packing material in chromosomes in sperm cells. There are two types of packaging, one seen predominantly in sperm uses protamines and the other is based on histones where the genetic material remains packaged in so-called nucleosomes. EVO-CHROMO research results suggest that chromatin organisation reflects not only transcription activity but also the type of promoter in which transcription starts. Tests on human sperm show that CpG island promoters retain a mixture of nucleosomes and subnucleosomal structures. The project team also looked at distal enhancers that stimulate gene promoters via chromatin looping mechanisms. Using the sea squirt Ciona of the Urochordates that are the closest vertebral relatives, the researchers found that conserved non-coding elements (ciCNEs) are associated with largely the same key regulatory genes as vertebrate CNEs. Furthermore, some of the tested ciCNEs can activate reporter gene expression in both zebrafish and Ciona embryos. Interestingly, tests on the fruit fly Drosophila showed that chromatin organisation is involved in intergenerational epigenetic inheritance characterised by an obesity model. Paternal high-sugar diet caused derepression of transcription control genes in heterochromatin in the early embryo and the sperm. Technological advances are enabling the study of the role of chromatin at the genomic scale. EVO-CHROMO research has provided a substantial knowledge base to continue this challenging area, an integral part of reproduction, development and evolution.
Keywords
Packing, genetic material, sperm, transcription, CpG, chromatin, nucleosomes