12 Developmental Gene Amplification

Abstract

In a number of organisms the DNA copy number of a small set of genes increases during specific times in development. This “developmental gene amplification” has evolved independently in widely different species and supports the rapid production of gene products that are required in high abundance during short developmental time windows. In several cases, it is known that amplification occurs because of site-specific re-replication from distinct origins using proteins that also govern genomic replication. Therefore, in addition to being an interesting developmental strategy for high-level biosynthesis, these amplified loci are models for origin structure and regulation in eukaryotes.

Here, I review the recent findings for three intensively studied amplification systems in the organisms, Tetrahymena thermophila, Sciara coprophila, and Drosophila melanogaster, which provide new insights into origin structure and regulation. Much of this evidence supports an important role for chromatin in the developmental regulation of origins. Readers interested in other details of these systems may consult several excellent reviews (Gerbi et al. 1993; Kapler 1993; Tower 2004; Claycomb and Orr-Weaver 2005).

First, it is important to distinguish developmental gene amplification, which results in the increase in copy number for a small number of specific gene loci, from the acquisition of polyploidy, which is an increase in copy number for most of the genome. In many cases, cells become polyploid through a special cell cycle known as the endocycle, comprising alternating G and S phases without mitosis (for review, see Lilly and Duronio 2005). During an endocycle S phase, most of the...