DEVELOPMENT: More Is Bigger

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Science  24 Mar 2006:
Vol. 311, Issue 5768, pp. 1677b
DOI: 10.1126/science.311.5768.1677b

Multicellular organisms can grow by making more cells or by making larger ones. The nematode Caenorhabditis elegans uses both methods: Cell proliferation drives worm growth until sexual maturity, whereas cell growth (mainly of epidermal cells) accounts for the twofold increase in size during adulthood. Growing adult cells also undergo endoreduplication, wherein genomic DNA is replicated repeatedly without cell division, resulting in each cell containing multiple copies of the genome (polyploidy) rather than just two.

Lozano et al. address the question of whether endoreduplication is directly responsible for adult growth in the worm. Blocking endoreduplication after the final larval molt results in dwarf worms that are roughly half the size of wild-type adults, whereas in a tetraploid strain, adult worms are roughly 40% larger than normal. Cyclin E is involved in the control of endoreduplication in a number of organisms, including C. elegans, and adult worms mutant for cye-1 have both reduced epidermal ploidy and are dwarfed, often to less than half the size of comparable wild-type adults. Although it is clear that endoreduplication can account for the growth of polyploid somatic cells in worms, cells that remain diploid in the adult are presumably stimulated to grow by their polyploid neighbors. — GR

Curr. Biol. 16, 493 (2006).

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