Date Published: April 30, 2012
Publisher: Impact Journals LLC
Author(s): Mathew D. McGee, Nicholas Day, Jill Graham, Simon Melov.
The C. elegans germline and somatic gonad are actively developing until the animal reaches adulthood, and then continue to undergo striking changes as the animal ages. Reported changes include a depletion of available sperm, a decrease in oocyte quality up till mid-life, a reduction in germline nuclei, a decrease in fertility, and an accumulation of DNA in the midbody of aging C. elegans. Here, we have focused on the aging gonad in old animals, and show in detail that the aging gonad undergoes a massive uterine growth composed of endoreduplicating oocytes, yolk, and expanses of chromatin. We use a novel series of imaging techniques in combination with histological methodology for reconstructing aged worms in 3-dimensions, and show in old animals growing masses swelling inside the uterus to occupy most of the diameter of the worm. We link this accelerated growth to the cep-1/p53 tumor suppressor. Because cep-1 is required for DNA damage induced apoptosis, and daf-2 limits longevity, these results suggest a role for age-related DNA damage in dysplastic uterine growths, which in some respects resemble premalignant changes that can occur in aging mammals.
Much of the pathobiology of aging C. elegans and the aging germline remains relatively poorly described despite the widespread use of C. elegans as a model system to study aging. The aging C. elegans germline has been reported to undergo a series of changes up to midlife [1,2]. After approximately 8 days of age, the pool of sperm that are produced during larval development are depleted and few viable embryos are produced despite a continuous supply of oocytes. In the absence of sperm, the buildup of RNP granules is thought to facilitate cell cycle arrest in unfertilized oocytes for up to several days [3,4]. Eventually, oocytes bypass the prophase I diakinesis arrest  but fail to fully complete anaphase I . Because they lack the sperm-contributed centrioles required for cytokinesis [7,8], these unfertilized oocytes would likely undergo endoreduplication [9,10] as worms age, rather than mitosis.
We have described in detail, a number of novel phenotypes in the aging C. elegans germline. Although age-related endoreduplication of unfertilized oocytes in middle aged animals has been commented on previously [1,11,16], we used a number of new techniques to describe the pathology of these masses and other age-related germline phenotypes in greater detail, and for the first time in older animals on different genetic backgrounds that may help shed light on the mechanism of age-related germline phenotypes in future studies. Most striking is the massive growth in the uterus that arises from unfertilized oocytes. These masses grow large enough to swell the uterus to fill most of the diameter of the worm. They are primarily composed of endoreduplicating unfertilized oocytes, masses of chromatin from presumably lysed nuclei, small clusters of individuals cells and/or nuclei, and yolk proteins. The growth of these uterine masses is accelerated in the cep-1/p53 mutant known to be required for DNA damage-induced apoptosis in C. elegans.
C. elegans strains were cultured using standard conditions  (N2, cep-1(gk138)I, daf-2(e1370)III, ced-3(n717)IV) or at the restrictive temperature of 25 degrees (glp-4(bn2)I,fem-2(b245)III) and obtained from the Caenorhabditis Genetics Center. Synchronized populations were acquired by allowing adult parents to lay eggs for 2-4 h before removing them (day 0). Worms were transferred daily to fresh plates during the reproductive period. Confocal microscopy, staining of tissue sections, and 3-D visualization was performed as described .