Somatic polyploidy supports biosynthesis and tissue function by increasing transcriptional output

Area of Science:

• Cellular biology
• Developmental biology
• Genetics

Background:

• Polyploidy, or increased DNA content, is hypothesized to enhance cell size and biosynthetic capacity in specialized tissues.
• The precise role and limitations of DNA concentration on cellular biosynthesis in vivo, particularly in non-disease states, remain underexplored.

Approach:

• Investigated the function of polyploidy in the C. elegans intestine, a tissue with high biosynthetic demands for yolk production.
• Artificially reduced the DNA/cytoplasm ratio in intestinal cells to assess the impact on cell size, mRNA concentration, and gene expression.
• Analyzed the compensatory mechanisms in response to altered DNA content, including RNA Polymerase II loading and translational machinery production.

Key Points:

• Polyploidy in the C. elegans intestine is essential for normal cell growth and yolk biosynthesis.
• Decreasing the DNA/cytoplasm ratio resulted in smaller cells with diluted mRNA, affecting highly-expressed transcripts more significantly.
• Lowly-expressed genes showed partial compensation through increased RNA Polymerase II loading on remaining genomes.
• Cells with reduced DNA content maintained normal total protein concentration by upregulating translational machinery at the expense of specialized proteins.

Conclusions:

• Cellular DNA concentration plays a critical role in regulating cell size and biosynthetic output, particularly in tissues with high metabolic demands.
• Polyploidy serves as an adaptive strategy to optimize cellular function and maintain homeostasis under varying genomic conditions.
• The findings provide insights into the regulatory mechanisms governing gene expression and protein synthesis in response to changes in DNA content in vivo.