Developmental gene amplification: insights into DNA replication and gene expression.

In the formation of a complex organism and the differentiation of specific cell types, there are often demands for high levels of particular gene products. These demands can be met by increasing transcription or translation, or by decreasing the rate of mRNA or protein turnover. Although these are the most common means to increase expression levels, there is another mechanism: gene amplification. Developmental gene amplification is a DNA replication-based process whereby specific genes are replicated above the copy number of surrounding sequences, resulting in an increase in the template available for transcription. Recent microarray studies in Drosophila melanogaster have identified two additional amplicons, suggesting that developmental gene amplification might be more widely used than was previously thought. Furthermore, work in both Drosophila and the related fly, Sciara coprophila, has yielded insights into the mechanisms, regulatory sequences and proteins controlling DNA replication during gene amplification, including a link between transcription factors and origin usage.