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Why does making new egg cells require so much cell death?

During egg production, roundworms create and then destroy oocytes with two nuclei

PLOS

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IMAGE: These are microtubules (red) in an apoptotic germ cell (far right) and four non-apoptotic germ cells. view more 

Credit: James R. Priess and colleagues

A highly detailed study of how the roundworm C. elegans forms oocytes suggests that the egg-making process leads to the formation and subsequent destruction of cells with an extra nucleus, but that some cellular materials are recycled into new eggs. James Priess of the Fred Hutchinson Cancer Research Center and colleagues, report these findings in a new study published July 19th, 2018 in PLOS Genetics.

When animals create egg cells, a large percentage of the potential eggs get culled through a controlled demolition process called apoptosis. Studies have shown that many of these sacrificed cells could go on to form healthy embryos, and researchers don't yet understand why animals target so many cells for destruction. In the current study, researchers used live imaging of microscopic cells to observe the formation of eggs inside the gonad of the model roundworm, C. elegans. They saw that when oocytes don't make the cut, they begin apoptosis by dumping their mitochondria, which act as the powerhouses of cell, into a shared pool of cellular material. The mitochondria then become recycled into new oocytes. The process also involves the formation of oocytes with two nuclei, but these always undergo apoptosis.

The study details the steps of cell death associated with egg formation and shows that the apoptosis machinery effectively recognizes two populations of cells, those with and without an extra nucleus. The researchers also observed early stages of apoptosis that had not yet been identified. These findings will aid future studies of egg development, as well as studies of Alzheimer's and Huntington's disease, which both cause certain types of damage to brain cells that are similar to apoptosis.

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In your coverage please use this URL to provide access to the freely available article in PLOS Genetics:

http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1007417

Citation: Raiders SA, Eastwood MD, Bacher M, Priess JR (2018) Binucleate germ cells in Caenorhabditis elegans are removed by physiological apoptosis. PLoS Genet 14(7): e1007417. https://doi.org/10.1371/journal.pgen.1007417

Image Credit: James R. Priess and colleagues.

Image Caption: Microtubules (red) in an apoptotic germ cell (far right) and four non-apoptotic germ cells.

Funding: JP is funded by grants from the National Institutes of Health RO1GM098583 and RO1GM107474

ME is funded by the Human Frontiers Science Program LT000267/2016

The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors declare that no competing interests exist.

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