Molecular Genetics

Endoreduplication results when replication is not coordinated to the cell cycle.

Facts

• Polytene chromosomes of Drosophila salivary gland cells (image from http://www.bionet.nsc.ru/booklet/images/imagesLaboratories/Zhimulev3Big.jpg) contain multiple copies of the chromosome's DNA. The process that leads to accumulation of the multiple copies is called endoreduplication. Endoreduplication also occurs in other tissues: the suspensor of plant embryos and the developing endosperm of cereal seeds.
• Endoreduplication can be limited to certain chromosome regions, such as that responsible for chorion synthesis in Drosophila.
• In most cells, the initiation of a round of DNA synthesis and initiation of mitosis are coordinated so that the DNA is replicated exactly once in each division cycle.

Interpretations

• Endoreduplication must occur by a disruption of the coordination between DNA synthesis and mitosis.
• The existence of endoreduplication suggests that the bicycle model of the cell cycle may be more representative of actual events than the more traditional unicycle model. In endoreduplication, the M cycle would be inactive and the S cycle freed from control by M cycle events.

Facts | Interpretations | Further Info. | Other Pages

Further information

• In chorion synthesis, the amplificative replication is initiated several developmental stages of egg chamber development before the initiated chains are elongated to complete replication (ref).
• MPF promotes mitosis. In developing maize endosperm, MPF protein phosphorylation activity declined dramatically at the onset of endoreduplication. The amount of P34 protein (a component of MPF) remained constant. In contrast, the amount and activity of S-phase-related protein kinases increased.
• Among other factors implicated in disruption of the DNA synthesis-mitosis coordination are cyclin E, escargot, and origin recognition complex 2.
• In A. thaliana, a topoisomerase-like enzyme, SPO11-3, is required for endoreduplication (ref) and is implicated as having a role in cell cycle checkpoint control (ref).

This is page 1335 of Molecular Genetics by Ulrich Melcher, © 1997, 1998, 1999, 2002, 2007, 2009