Endoreduplikatsioon

Endoreduplikasjon, or endoreduplication, is a cellular process in which the genome is replicated without subsequent cell division, yielding cells with increased DNA content (polyploid) or multinucleate cells. In this mode, the cell undergoes rounds of DNA synthesis (S phase) but either does not enter mitosis or fails to complete cytokinesis, so the usual division into two daughter cells does not occur. The result is an enlarged cell size and, in some tissues, higher metabolic or synthetic capacity.

Endoreduplikasjon can occur via different routes. A common form is endocycle cycling, where successive S phases alternate with gap phases (G or G2) without mitosis. Another route is endomitosis, in which the cell enters mitosis but mitotic events are incomplete, and cytokinesis does not complete. Distinctions between these routes are sometimes blurred in practice, but the core feature is genome amplification without normal cell division.

Biology and occurrence: Endoreduplikasjon is widespread in plants and is also observed in various invertebrates and some vertebrate tissues. In plants, it is particularly frequent in developing leaves, fruits, endosperm, and trichomes, where increased cell size and metabolic output can support organ growth and function. In animals, polyploid cells arise in tissues such as the liver, placenta, and certain blood cells.

Functions and regulation: Endoreduplikasjon is often developmentally programmed and can be stimulated by environmental cues or stress. It is regulated by cell cycle control genes, including cyclin-dependent kinases and their inhibitors, as well as hormonal and epigenetic factors. While it supports tissue growth and function in many contexts, polyploidy can also influence gene expression patterns and genome stability.