Eukaryotic DNA replication origins: many choices for appropriate answers.

At each cell division in humans, 30,000-50,000 DNA replication origins are activated, and it remains unclear how they are selected and recognized by replication factors. DNA replication in multicellular organisms must accommodate variations in growth conditions and DNA damage. It must also adapt to changes in chromatin organization associated with cell differentiation and development. The selection of replication origins in metazoans seems to involve multiple choices, with the appropriate answers depending on the identity of the cell or the conditions of growth. This suggests that during evolution, the use of replication origins became more controlled by epigenetic mechanisms affecting chromosome dynamics and expression than by DNA synthesis per se.