How Nuclear Structure and Organisation Influence Gene Expression
Mankind is defined by a genetic blue-print encoded in a haploid genome of roughly 3 x 109 bp of DNA. Simplifying the locating of genes responsible for different genetic defects has been one of the justifications behind initiatives to sequence the human genome. Once the sequence and location of putative genes is established it is a relatively simple matter to identify cell types in which they are expressed. A better understanding of gene function in mammalian cells will be part of the solution in identifying how different diseases might be related to individual genetic defects.
DNA sequence provides the information required to activate gene expression. However, eukaryotic nuclei are so intricate that this information is not sufficient to predict either levels or patterns of gene expression in individual cells. A variety of epigenetic features must influence critical aspect of nuclear function in mammalian cells.
The aim of our research is to establish how nuclear structure and organisation influence gene expression in mammalian cells. We have shown that eukaryotic nuclei are highly structured and that the major nuclear processes all take place at specialised nuclear sites (Figure 1). Dedicated nuclear sites can be identified in cells growing in medium supplemented with the transcription precursor analogue Bromo-uridine. This is introduced into the nascent RNA chains and can be subsequently identified using specific antibodies. In this example, the sites of transcription (green) are distributed throughout the dispersed euchromatin (blue - a green fluorescent protein-histone shows the distribution of open and condensed chromatin) and excluded from the speckles (red - immunostained for Sm proteins) that define an important nuclear compartment involved in RNA processing. Interactions within these compartments generate chromatin domains that are intimately linked to gene expression and form part of an organisational hierarchy that must be fundamental to both the structure and function of eukaryotic chromatin. Understanding how chromosome structure and nuclear organisation influence gene expression is of fundamental importance. A detailed picture of the features that influence gene expression is vital if we are to be successful in developing gene therapy.
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The Leukaemia Research Fund, BBSRC