| The Details of Gene Expression |
What regulates gene expression? The general principles of eukaryotic gene regulation are now well known. Much regulation occurs during transcription as RNA is synthesized from the DNA template. This process is mediated by interactions between proteins and DNA and, sometimes, interactions between different proteins. Proteins called transcription factors bind to DNA sequences, known collectively as regulatory elements, located near the coding region of the gene in question
(Fig. 1). When proteins bind to the regulatory elements, it alters the transcriptional machinery and, thus, the level of transcription can change. In some cases the binding of transcription factors to the regulatory elements causes transcription to increase (up-regulation); in other cases it causes transcription to decrease (down-regulation).
The invention of microarray chips in the late 1990s enabled researchers to observe the expression patterns of thousands of genes at the same time. (See the Genomics unit.) Using these chips, researchers can compare the genomic expression patterns of different cell types (such as a neuron versus a liver cell), as well as examine the changes in these patterns that occur as an embryo develops. With the microarray assays, biologists found many previously undiscovered genes that play a role in development. By examining groups of genes that have correlated changes in their expression patterns, biologists have inferred groups of genes that may interact in developmental pathways. They then use other methods to determine whether the hypothetical pathways actually exist.