The expanding implications of polyploidy

Abstract

Polyploid cells, which contain more than two genome copies, occur throughout nature. Beyond well-established roles in increasing cell size/metabolic output, polyploidy can also promote nonuniform genome, transcriptome, and metabolome alterations. Polyploidy also frequently confers resistance to environmental stresses not tolerated by diploid cells. Recent progress has begun to unravel how this fascinating phenomenon contributes to normal physiology and disease.

Figure 1.

Genomic alterations associated with polyploidy. (A) Polyploid genomes can contain both over- and underreplicated regions, represented by array or sequencing strategies that detect differences in gene copy number across the genome. (B) Polyploid genomes can undergo frequent deletions. Shown here is an example of gene deletion creating a new locus, as in O. trifallax. (C) Polyploid cells can undergo and tolerate multipolar divisions with supernumerary centrosomes (green dots) and tripolar mitotic spindles (green lines). These divisions lead to chromosome missegregation and aneuploidy, as they can divide genomic material (blue) intended for two cells into three daughters instead. (D) The mechanisms shown in A–C are all well tolerated by the polyploid state and can create genetic heterogeneity in tissues or in cell populations. As diploid cells (blue circles) polyploidize, the mechanisms in A–C can create a tissue made up of cells that are no longer genetically identical (represented by enlarged polyploid cells of different colors).

Figure 2.

Cellular strategies for stress tolerance through polyploidy. Polyploidization is a commonly used strategy for tolerating numerous environmental and cellular stresses. (top) Polyploidization may occur developmentally or in response to environmental stress, leading to recurring transcriptional/metabolic changes that confer stress tolerance (purple state). (bottom) Polyploidization may generate genomic heterogeneity (Fig. 1), which in response to stress facilitates selection for stress-resistant phenotypes.