THE AGING REPRODUCTIVE SYSTEM Click pictures for new window with figure and legend, click again for high resolution image THE AGING REPRODUCTIVE SYSTEM Click pictures for new window with figure and legend, click again for high resolution image
1 General Description
The C. elegans reproductive system produces mature gametes and also provides the structure and environment for fertilization, early embryonic development and egg-laying. The hermaphrodite reproductive system consists of three major regions: 1) the somatic gonad, including the distal tip cell (DTC), gonadal sheath, spermatheca (sp), spermathecal-uterine (sp-ut) valve, and uterus; 2) the germ line with mitotic and undifferentiated cells in the distal region that become meiotic and specialized as they progress through the proximal arm; and 3) the egg-laying apparatus, consisting of the vulva, uterine and vulval muscles and specialized neurons. (AReproFIG 1; For detailed description see Hermaphrodite Somatic Gonad, Germ Line and Egg-Laying Apparatus sections.) In hermaphrodites, sperm production only occurs in larval stages since at the adult molt, germline precursors switch to forming oocytes. However, males produce sperm continuously throughout adulthood.
AReproFIG 1: Structure of the adult hermaphrodite reproductive system.A.Schematic of the adult hermaphrodite, lateral view, left side, showing the location of the reproductive system within an intact animal. The reproductive system has twofold symmetry and consists of two U-shaped gonad arms joined to a common uterus. The reproductive system opens to the environment via the vulva, located in the ventral midbody. B. Differential interference contrast (DIC) microscopy image of an adult anterior gonad arm from boxed region in A. The extent and location of mature somatic gonad tissues are indicated by the color overlay. (DTC) Distal tip cell; (DG) distal gonad; (PG) proximal gonad; (Sp) spermatheca; (Sp-ut) spermathecal-uterine valve. Magnification, 400x. (Based on Kimble and Hirsh, 1979; McCarter et al., 1997.) See also Hermaphrodite Somatic Gonad.
The Caenorhabditis elegans germline and somatic gonad undergo complex changes during larval development and achieve peak mature function during the first several days of adult life. Although the animal can sometimes survive for 2-3 weeks as an adult, its fertile period ends after one week. Thereafter, the body shrinks in volume, becomes relatively fragile and decrepit, and reproductive capability declines sharply. While the somatic gonad remains fairly intact, it is diminished in productivity due to a depletion of sperm, decrease in oocyte quality, reduction in germline nuclei, and decreased fertility. Germline nuclei show lower levels of DNA double-strand break induction and repair (Toraason et al., 2022). Hermaphrodites can recover some fertility after depleting self-sperm by mating with a male and receiving the male's sperm. However, in the absence of male mating, germline cells still continue to divide, producing excess germline-derived tissue that accumulates in the midbody as a germline tissue "tumor" (AReproFIG 2; AReproVID 1 & AReproVID 2).
AReproFIG 2: Illustration showing progressive changes in the germline with age. In young adults, eggs are fertilized as they pass through the spermatheca. In middle-aged adults, egg-laying declines and fertilized and unfertilized embryos can collect in the uterus. In older adults, complex germline masses can eventually expand to fill much of the body cavity of the animal. The vulva often appears plugged. (Figure reproduced from Herndon et al., 2007). AReproVID 1&2: Videos of cross-sections of young and old worms. Videos are created from aligned methylene blue/pararosaniline cross sections and progress from the nose to tail of the animals. A few anatomical structures are labeled. AReproVID 1 is from a 1-day-old adult wild-type worm. Distal gonad arm is visible from 8-22 seconds and then from 27-40 seconds. From 20-25 seconds, the intestine becomes visibly squished to a smaller volume as the enlarged uterus fills much of the interior cavity. While the tissue appears to spiral around due to an alignment artifact, it actually lies toward the dorsal pole in this region near the uterus. The vulva is in view from 26-28 seconds. The anterior and posterior spermathecae are visible at 17 and 34 seconds respectively. AReproVID 2 is from a 17-day-old wild type adult worm with the distal gonad visible between 10-19 and 43-47 seconds. The intestine and other tissues become visibly squished to a much smaller volume by the presence of a large germline tumor at two points along the length of the animals, shown from 21-26 seconds and again between 38-40 seconds. The vulva is seen from 29-31 seconds and is extremely compressed by the large germline mass. The anterior and posterior spermathecae are visible at 20 and 45 seconds respectively. As in AReproVID 1, at points the intestine appears to spiral, but this effect is an artifact of the alignment of the video frames. (Video Source: McGee et al., 2011.) See also AReproFIG 7 for further details.
The number of active germline cells within the “progenitor zone” decreases notably as the adult ages, even while the animal continues to lay eggs (Garigan et al., 2002; Killian and Hubbard, 2005; Luo et al., 2010; Kocsisova et al., 2019), and the distal portion of each gonad arm becomes notably foreshortened in late adulthood. The gonad produces hormonal signals associated with reproductive status that regulate somatic cell functions (Baxi et al., 2017) and declines in reproductive hormone signaling pathways during the postreproductive period lead to functional and structural changes in these somatic tissues. In older adults, fewer and fewer mature oocytes are available to absorb the yolk continuously secreted by the intestine, and as a result, the pseudocoelom begins to fill with this excess yolk (AIntFIG 4; Herndon et al., 2002). The timing of the build-up in yolk varies animal to animal, but is usually first seen around 7 days of adulthood. As the animals continue to age, yolk accumulation in the pseudocoelom is more reliably seen. Excess yolk is not found inside the tumorous germline tissues nor among the uterine contents, as yolk can apparently only enter the germline via healthy primary oocytes (Hall et al., 1999).
2 Somatic Gonad Changes During Aging
Analysis of the somatic gonad indicates that some tissues appear remarkably healthy during the early stages of aging. The spermatheca, uterine epithelium, vulval epithelium and vulval muscles are still recognizable and appear “functional” in static views by TEM, despite the obvious failure of lumenal materials to escape. This suggests that failure in egg-laying may result from a lack of normal nerve/muscle signaling to the sex muscles (cf. Toth et al., 2012).
The status of the gonad sheath cells and of the uterine sheath in aging adults is harder to determine. Both tissues must remain intact, since there is no evidence for their lumenal contents escaping into the pseudocoelom. At 7 days of adulthood, both of these epithelial tubes remain inflated with germ cell contents, to the virtual exclusion of other fluids, whereas in younger adults the uterine lumen contains fertilized embryos floating in a sea of fluid. However, by 15 days of adulthood these two epithelial tubes and the connecting spermatheca are highly distorted by the swollen nature of the germline tissues, and the boundaries between one tissue and the next become unrecognizable, even at the EM level.
The spermatheca remains recognizable at 7 days of adulthood, although its lumen tends to be much more open than in young adults (AReproFIG 3). In young adults, the spermatheca acts as a reservoir for available sperm and as a valve blocking easy flow from gonad arm into the uterus (see SomaticFIG 9B-D), but by 7 days of adulthood, neither of these functions is still operative. The spermathecal tube no longer contains sperm and has relaxed enough to allow some flow of germline cells between gonad and uterus, possibly in both directions. At even later stages, the spermathecal valve becomes stuck open and filled with germline debris
AReproFIG 3: Changes in the spermatheca with age.A. In young adult (1-2day) the spermatheca (outlined in blue) is characterized by a nice smooth outer edge. Cytoplasm is rich in organelles, including RER and mitochondria. Sperm are present (white arrow). Insets show enlarged boxed regions with black arrows showing pleated septate junctions. Magnification 600x. Scale bar 3µm. (Image source: N2-1232 [Hall] 17.) B. In slightly older animals (~3 day adult) the spermatheca has a shrunken cytoplasm with a highly irregular border. Cytoplasm of the valve cells is vacuolated and depleted of mitochondria and ribosomes. Sperm are not easily detected and septate junctions are prominent. (Image source: N2U [MRC] 13540.) C. In a 15-day-old adult, the outer border is convoluted, and the valve is impacted by debris (white arrow). Cytoplasm has enhanced electron density and is lacking organelles. Septate junctions remain visible. (Image source: N815 [Hall] G0714; class B.)
3 Distal Gonad Aging
During the aging process, the distal arm of the gonad appears to shorten, and possibly becomes less active, accompanied by a decrease in length of the progenitor zone. In some cases, the germline can display a shifted distal tip cell (DTC) nucleus (Kocsisova et al., 2019). The germ cells still display a bare zone filled with mitotic cells attached to a central rachis (forming a syncytium), but the region appears less organized in older animals with greater spacing among the nuclei (AReproFIG 4). It also becomes difficult to recognize the position of the spermatheca, which is still used as a marker for the border between uterus and gonad sheath (McGee et al., 2011). Similarly, the connection of the distal arm of the gonad to the proximal arm is also difficult to detect, due to the immense enlargement of the latter. It is likely that the expansion of the germline tumor begins shortly before 7 days, and that events such as the breaching of the spermatheca to allow the germline mass to push into the gonad arm occur at any time after 7 days. The timing is likely different from animal to animal, and exceedingly few wild type animals actually survive to 15 days (Herndon et al., 2002).
AReproFIG 4: Aging of the distal gonad. Transmission electron micrograph of a cross section from the distal gonad arm of a young adult (A) and a 7 day-old wild-type worm (B). Nuclei (N) are in separate cells enclosed by plasma membranes. These cells are connected by narrow cytoplasmic bridges or to local zones of rachis (R) that do not contain any nuclei, but only a shared cytoplasm. Compared to the younger distal arm, the aging germline shows several large spaces between adjacent nuclei; they are not clustered so tightly, nor apparently dividing as fast, as in young gonad. In older animals, the pseudocoelom is often filled with yolk particles. Nearby bodywall muscle (BWM) is thinned, but still well connected to the overlying cuticle, which is greatly thickened in the older animal. (Image source: A N533 [Hall] G4 F444; B N824 [Hall] B2 86-87, class B.)
The distal germline, including an unsheathed zone, is retained and still holds a portion of syncytial germline in apparent mitosis at 7 days. As the animals continue to age, there is more pathology, with the loss of many germline cells. The distal arm becomes shorter and shorter, but is still distinguished by immature cells clustered around the rachis and the distal tip cell (Killian and Hubbard, 2005). After day 5 of adulthood, the distal tip cell can sometimes become displaced from its normal position making it hard or impossible to find (Kocsisova et al., 2019; Scharf et al., 2021). This late defect was noted in mated adults, but it may also occur at some point in older unmated hermaphrodites as well, which might be why in TEM studies of older adults, the distal tip region of the germline could be identified in serial sections, but sometimes with no evidence of the DTC (D. Hall, unpublished).
There are known to be important gap junctions connecting the distal germline to the distal tip cell and to the somatic sheath (Starich et al., 2014) which are influential in the progression of germline cells through mitosis and meiosis. However, the tiny sizes of these many junctions precludes their visualization by standard TEM even in young adults so that their continued patency during aging remains unknown.
4 Sperm Depletion and Oocyte Aging
During aging, the germline undergoes a series of changes (Garigan et al., 2002; Herndon et al., 2002; Collins et al., 2008; Luo et al., 2010; McGee et al., 2012). In hermaphrodites, at about 5-6 days of adulthood, the pool of sperm that are produced during larval development are depleted and no more viable embryos are produced despite a continuous supply of oocytes. A hermaphrodite animal that mates with a male gains more sperm and can continue to lay fertilized eggs for another day or two (Hughes et al., 2007; Tolkin and Hubbard, 2021), though progeny production still declines even in the presence of sperm due to aging of the reproductive tract (Hughes et al., 2007; Kocsisova et al., 2019). There is some evidence that mated hermaphrodites can undergo a shrinking phenotype with much more rapid aging, possibly produced by exposure to male seminal fluid (Shi and Murphy, 2014; Scharf et al., 2021).
For some days after sperm depletion, the hermaphrodite collects unfertilized eggs in the uterus and then expels them (Klass, 1977; Croll et al., 1977). In the absence of sperm, the oocytes undergo cell cycle arrest. The majority of the contents of the uterine lumen after 7 days of adulthood is composed of unfertilized oocytes. These cells adopt several different morphologies. Some oocytes show cortical granule activation, despite a failure of sperm entry. This sham version of fertilization results in a distinctive scalloped appearance due to the delivery of these large clear vesicles to the oocyte borders but there is a failure to produce either a fertilization membrane or an eggshell. Due to cortical granule activation occurring near the time of passage through the spermatheca, as it would in a younger adult when sperm are still present, many of these types of oocytes are found near the spermatheca (see AReproFIG 5). Farther from the spermatheca, the borders between oocytes disappear as they merge into syncytial masses. Oocytes deeper into the uterus rarely show activation, but their nuclei are often dramatically larger in size. Apparently lacking factors required for cell polarization and cytokinesis (Gonczy and Rose, 2005), these unfertilized oocytes then begin to undergo endoreduplication (Ward and Carrel, 1979; McGee et al., 2012; AReproFIG 6) rather than mitosis. Their nuclei increase in size as the chromosomes are repeatedly duplicated in place. Germ cell production continues apace in the distal arm (AReproFIG 5), while the uterus begins to collect a diverse set of germline products, including a few fertilized embryos, and many more unfertilized oocytes (AReproFIG 5 & AReproFIG 9).
AReproFIG 5: Germline products in aging hermaphrodites.A. Longitudinal view showing the germline of a young adult. Immature germ cells are seen at the top of the distal arm. In the proximal arm, mature oocytes are getting ready to enter the spermatheca. Fertilized embryos can be seen on the right side of the spermatheca and progress towards the vulva where they are laid after undergoing a few rounds of cell division. Scale bar: 25 µm. (Image source: N1-1402 [Hall]). B-D. Products seen in the reproductive tract of 7-day-old post reproductive adults. B. An unfertilized oocyte is featured undergoing acrosomal activation involving release of large white vesicles at the outer edge of the cell (arrowheads), but this cell is not producing an eggshell. This is probably a spontaneous event occurring just after passage through the spermatheca. (Image source: N953 [Hall] D3 206, class A.) C. Advanced embryo, seen at lima bean stage surrounded by blastocoel (Bl) and an eggshell (ES) (Image source: N953 [Hall] J3 091, class A.) D. Improperly developed embryo retained in the uterus. (Image source: N824 [Hall] E4 204, class B.)
Farther from the spermatheca, the borders between oocytes disappear as they merge into syncytial masses. Concurrent with sperm depletion, a progressive decrease in oocyte quality reduces the likelihood of the development of viable embryos in older hermaphrodites even in the presence of viable sperm (Hughes et al., 2007; Luo et al., 2010; Tolkin and Hubbard, 2021; Cota et al., 2022). This age-related decrease in oocyte quality occurs at least partially through the insulin signaling and TGF-β pathways (Collins et al., 2008; Luo et al., 2010). Low quality oocytes can show various defects including small size, cavities, or clusters of oocytes in the uterus (Luo et al., 2010; Cota et al., 2022). The apoptotic pathway is also required to maintain oocyte quality, as a loss of apoptosis in the germline causes an early loss of reproductive capacity and an earlier incidence of abnormal oocytes (Andux and Ellis, 2008).
AReproFIG 6: Oocyte deterioration and germline mass formation in aging gonad. Top: Representative oocyte quality images of mated adults. N2 at Day 1 and Day 8 adult. White arrows indicate oocytes or developing embryos, white dotted outline marks uterine mass. Scale bar is 20m. (Image source: Cota et al., 2022, reproduced with permission from C. Murphy.) Bottom: Cross-section views of midbody from young and 15-day-old adults. In older animals germline tissue can occupy more than 90% of the total volume, with intestine (int), bodywall muscle (BWM) and hypodermis (hyp) pushed to extremely thin slivers at the periphery, and reducing the pseudocoelom to extremely narrow passageway. A few immature oocytes are still present that look almost normal, but are stranded far from the spermatheca. A complex germline tumor occupies almost the entire volume, including a massive overgrowth of tightly compacted nuclear material. Scale bar: 10 µm. (Image source: left panel - N903A [Hall] X709; Right panel - N816 [Hall] H0027, class B.)
5 Accumulation of Germline Products and Germline Masses
The earliest appearance of unfertilized oocytes in the uterus is seen around 6 days of adulthood, at which time the mother is still able to pass them through the vulva, thus laying a mixture of healthy fertilized eggs (ovoid, with eggshells) and rounded inviable oocytes. If mated, hermaphrodites will continue producing healthy eggs for a longer time than unmated animals, up to 8 days of adulthood (Ward and Carrel, 1979; Luo et al., 2010) while after 10 days of adulthood, hermaphrodites no longer lay eggs, viable or not. Instead these animals display a moderately swollen uterus that is filled with a mixture of germline products (AReproFIG 9), most of which appear to be still alive and changing over time. The proximal arm of the gonad can dominate the midbody cross-section virtually to the same extent as does the uterine expansion, and both are filled primarily with syncytial tissues. In these older animals oocytes continue to accumulate in the uterus, and can force themselves back into the ovary, eventually spanning most of the diameter of the worm. This causes other organ systems, such as intestine and muscle, to become compressed, likely compromising function (AReproFIG 6; AReproFIG 7) (Herndon et al., 2002; McGee et al., 2011; McGee et al., 2012).
Examination of the germline masses by staining of sectioned tissues and imaging by light microscopy (Golden et al., 2007; McGee et al., 2011; McGee et al., 2012) or transmission electron microscopy (Herndon et al., 2007; L. Herndon and D. Hall, unpublished) reveals sectors with distinct characteristics: cellularized regions with similar appearance to somewhat small primary oocytes, and large syncytial zones featuring clustered nuclei or chromatin masses in progressive stages of degeneration, and large zones of cytoplasm that can also show regional differences. By 15 days, the increasing size of the germline mass has forced it to expand outward inside the uterus and press against neighboring tissues, compacting the bodywall muscle and the intestine until the uterine tumor can fill up to 90% of the animals profile in cross-section. Expansion of this germline tissue also creates enough force to push back to the anterior and posterior regions and even through the spermatheca and into the gonad sheath (AReproFIG 6, AReproFIG 7, AReproFIG 8).
AReproFIG 7: Germline masses in aging worms. A. Partial maximum projection of mid-section of whole wild-type worms stained with DAPI at 1, 5, 9, 13, and 17-days-old raised at 20 degrees. Arrow indicates the -1 oocyte in diakinesis (none visible in 17-day-old worm). Asterisk indicates spermatheca. Large arrowhead indicates unfertilized, endomitotic nuclei. # indicates a mass that has no distinct cellular structure. Small arrowhead in the 17-day-old indicates site of invasion from uterus to spermatheca. Scale bar represents 100 µm. B. Cross sections of the same 17-day-old wild-type worm stained with pararosaniline and methylene blue starting at approximately -1 oocyte position along anterior half (i). Remaining sections are spaced 50 µm apart (ii-viii), moving towards posterior and ending at approximately -1 oocyte position along posterior half (viii). In some cross sections, the uterine growth has taken up nearly the whole diameter of the worm (ii, iii, vii). Growth recedes at midbody (iv). Intestine (int), distal gonad arm (dga), proximal gonad arm (pga), and uterus (ut) are indicated. (Image source: McGee et al., 2012, with permission from S. Melov.) See also AReproVID 1 & AReproVID 2.
While some germline regions contains seemingly intact nuclei, with regions of cytoplasm between them, other areas contain clusters of nuclei with no visible cytoplasm separating them and can show some nuclear envelope degradation. The most severely corrupted regions contain masses of DNA with no visible nuclear envelope or cytoplasm. Progressive alterations in nuclear envelope morphology, such as blebbing and fragmentation, have been previously documented as part of the age-related degenerative process in C. elegans (Haithcock et al., 2005; R. Androwski and M. Driscoll, pers. comm.). There is a visible decrease in electron density of the DNA and DAPI staining in the more degenerated chromatin masses, suggesting that there is a shift in chromatin state from heterochromatin to euchromatin
AReproFIG 8: Oocyte deterioration and germline mass formation in aging gonad. A. Low power image shows a portion of a germline tumor enclosed by a thin gonadal sheath cell (black arrows). Nearby pseudocoelom is filled with excess lipid (L) and yolk (Y). Within the tumor there are regions jammed with many nuclei and regions of complex cytoplasm, but no obvious maturing oocytes. Boxed region (B) is shown at higher magnification. Each asterisk indicates a separate nucleus separated by plasma membranes from one another. (Image source: N801 [Hall] E564, 15 day old class B.) Scale bar is 1 µm. C. Transmission electron micrograph of a cross section from the distal gonad arm of a 15-day-old wild-type worm. Nuclei (N) are in separate cells enclosed by plasma membranes. Compared to younger distal arm (AReproFIG 4A), this aging germline shows several large spaces between adjacent nuclei. This portion of a distal gonad arm is only rarely enclosed by a sheath cell (black arrowheads), but often shows local whorls of basement membrane (bm) rather than a single layer surrounding unsheathed portions. The pseudocoelom is filled with yolk particles (Y). Nearby bodywall muscle (BWM) is thinned, but still well connected to the overlying cuticle. In a separate arm of the gonad at the lower right, a single oocyte remains enclosed by a gonadal sheath (S), and contains multiple yolk granules. Such evidence for maturing oocytes in aging gonad is rare. (Image source: N812 [Hall] H006, 15 day old class A.) Scale bar is 5 µm.
6 Egg-Laying Apparatus in Aged Adults
Young adults (1 or 2 days of adulthood) contain newly fertilized oocytes in the uterus, and little else (AReproFIG 5A, AReproFIG 9A). In contrast to what is seen in aging animals, the uterus of young hermaphrodites often contains empty space which can comprise half of the uterine volume and is fluid-filled, providing the avenue for eggs to move easily towards the vulva, and for male-provided sperm to swim towards the spermatheca (see examples on SlidableWorm sections 326 to 476 - labels off). After self-sperm have been depleted and the hermaphrodite is no longer laying fertilized eggs, the passageway through the vulva often becomes blocked by germline debris, and it is possible that the egg-laying muscles may deteriorate in function, although they physically appear rather healthy. The uterus becomes highly inflated, perhaps two or three times that of a young adult, and is completely filled by solid objects with virtually no free space (AReproFIG 9B-D).
AReproFIG 9: Egg-laying apparatus in aging hermaphrodites. Panels each are centered on lengthwise views of the vulva (black arrowhead) (ventral side down) in a young adult (A) and in several 15-day-old animals (B-D). A. Uterus is filled by developing embryos, with older embryos nearest the vulva, and younger embryos closer to the spermathecae (for expanded view see AReproFIG 5A). Healthy intestine is seen along the dorsal side above the uterus. Healthy vulval muscle (VM) cluster to either side of the vulval epithelium. Scale bar: 10 µm. (Image source: N1-1402 [Hall].) B. Uterus is grossly swollen with loosely packed germline debris (GD), some of which is blocking the vulval opening which may cause any fertilized oocytes produced late in adulthood to develop within the uterus causing a "bag of worms" event (see main text). The intestine still lies dorsally, but is squished into a narrower profile, thicker on the left side, but almost absent on the right. Vulval muscles appear present on either side of the vulval opening, but much reduced in volume. No intact embryos are seen. Magnification 600x. Scale bar: 20 µm. (Image source: N2 -1508-2 [Hall].) C. Uterine volume is filled with dense-staining germline material without any intact embryos. The vulva is forced partially open by the tumorous germline products, and vulval muscles are difficult to discern. Along the dorsal side, a distal gonad (DG) arm lies just above the vulva, with a rather degraded intestinal lobe evident to the upper right side, and possible yolk patches in the pseudocoelom to the upper left. (Image source: N815 [Hall] G984.) D. Uterus is swollen with accumulated germline debris and a large mass of yolk presses down from the dorsal side, squeezing the uterus locally. The intestine is not seen, possibly pressed away from the midline by the mass of yolk (Y). Vulval muscles and likely vulval epithelial cells are seen on either side of the vulva, which is closed. Magnification 600x. Scale bar: 20 µm. (Image source: N2-1508-2 [Hall].)
The principal synaptic inputs to the vulval muscles come from HSN, VCs and a few other ventral cord motor neurons (White et al., 1986). The vulval muscles still appear intact at 7 days, suggesting that loss of neuromuscular inputs may happen earlier to end contractility. Inputs to the uterine muscles occur only via gap junctions from the vulval muscles (White et al., 1986); therefore activity of the uterine muscles should also decline when the vulval muscles lose NMJ inputs, and there should be virtually no forces on the uterus to push materials out of the uterus and through the vulva. The presence of Age-associated vulval integrity defects (Avid) such as those found in herniated, ruptured or exploded worms, have been correlated with longevity in populations of worms and have been proposed as a marker of nematode healthspan (Leiser et al., 2016). When the vulval opening becomes blocked, remaining fertilized embryos inside the uterine lumen can continue to develop and hatch inside the mother. Such “bag of worms” events (aka “matricidal hatching”) are fatal to the mother, as internal hatchees can then consume her from the inside (Luc et al., 1979; Pickett and Kornfeld, 2013; Scharf et al., 2021).
7 References
Andux, S. and Ellis, R.E. 2008. Apoptosis maintains oocyte quality in aging Caenorhabditis elegans females. PLoS Genet. 4: e1000295 doi: 10.1371/journal.pgen.1000295
Baxi, K., Ghavidel, A., Waddell, B., Harkness, T.A. and de Carvalho, C.E. 2017. Regulation of Lysosomal function by the DAF-16 forkhead transcription factor couples reproduction to aging in Caenorhabditis elegans. Genetics 207: 83-101. doi: 10.1534/genetics.117.204222
Collins, J.J., Huang, C., Hughes, S. and Kornfeld, K. 2008. The measurement and analysis of age-related changes in Caenorhabditis elegans. WormBook. ed. The C. elegans Research Community, WormBook, doi: 10.1895/wormbook.1.137.1
Cota, V., Sohrabi, S., Keltsky, R. and Murphy, C.T. 2022. Oocyte mitophage is critical for extended reproductive longevity. PLoS Genet. 18:e1010400 doi: 10.1371/journal.pgen.1010400
Croll, N.A., Smith, J.M. and Zuckerman, B.M. 1977. The aging process of the nematode Caenorhabditis elegans in bacterial and axenic culture. Exp. Aging Res. 3: 175–189. doi: 10.1080/03610737708257101, PDF
Garigan, D., Hsu, A.L., Fraser, A.G., Kamath, R.S., Ahringer, J. and Kenyon, C. 2002. Genetic analysis of tissue aging in Caenorhabditis elegans: a role for heat-shock factor and bacterial proliferation. Genetics 161:1101–1112. doi: 10.1093/genetics/161.3.1101, PDF
Golden, T.R., Beckman, K.B., Lee, A.H.J., Dudek, N., Hubbard, A., Samper, E. and Melov, S. 2007. Dramatic age-related changes in nuclear and genome copy number in the nematode Caenorhabditis elegans. Aging Cell 6:179-188. doi: 10.1111/j.1474-9726.2007.00273.x
Gonczy, P. and Rose, L.S. 2005. Asymmetric cell division and axis formation in the embryo. WormBook. ed. The C. elegans Research Community, WormBook, doi: 10.1895/wormbook.1.30.1
Haithcock, E., Dayani, Y., Neufeld, E., Zahand, A.J., Feinstein, N., Mattout, A., Gruenbaum, Y. and Liu, J. 2005. Age-related changes of nuclear architecture in Caenorhabditis elegans. PNAS 102: 16690-16695. doi: 10.1073/pnas.0506955102, PDF
Hall, D.H., Winfrey, V.P., Blauer, G., Hoffman, L., Furuta, T., Rose, K.L., Hobert, O. and Greenstein, D. 1999. Ultrastructural features of the adult hermaphrodite gonad of C. elegans: Relations between the germ line and soma. Dev. Biol. 212: 101-123. doi: 10.1006/dbio.1999.9356, PDF
Herndon, L.A., Schmeissner, P.J., Dudaronek, J.M., Brown, P.A., Listner, K.M., Sakano, Y., Paupard, M.C., Hall, D.H. and Driscoll, M. 2002. Stochastic and genetic factors influence tissue-specific decline in ageing C. elegans. Nature 419: 808-814. doi: 10.1038/nature01135, PDF
Herndon, L.A., Wolkow, C.A., Driscoll, M. and Hall, D.H. 2017. Effects of ageing on the basic biology and anatomy of C. elegans. In Ageing: lessons from C. elegans. (ed Olsen, A. and Gill, M.). Chapter 2. pp. 9-39. Springer International, Switzerland. doi: 10.1007/978-3-319-44703-2_2, PDF
Hughes, S.E., Evason, K., Xiong, C. and Kornfeld, K. 2007. Genetic and pharmacological factors that influence reproductive aging in nematodes. PLoS Genet. 3: e25. doi: 10.1371/journal.pgen.0030025
Killian, D.J. and Hubbard, E.J.A. 2005. Caenorhabditis elegans germline patterning requires coordinated development of the somatic gonadal sheath and the germ line Dev. Biol. 279: 322-35. doi: 10.1016/j.ydbio.2004.12.021
Kimble, J.E. and Hirsh, D. 1979. The postembryonic cell lineages of the hermaphrodite and male gonads in Caenorhabditis elegans. Dev. Biol. 70: 396-417. doi: 10.1016/0012-1606(79)90035-6, PDF
Klass, M. 1977. Aging in the nematode Caenorhabditis elegans: major biological and environmental factors influencing life span. Mech. Ageing Dev. 6: 413-29. doi: 10.1016/0047-6374(77)90043-4, PDF
Kocsisova, Z., Kornfeld, K. and Schedl, T. 2019. Rapid population-wide declines in stem cell number and activity during reproductive aging in C. elegans. Development 146: dev173195. doi: 10.1242/dev.173195
Leiser, S.F., Jafari, G., Primitivo, M., Sutphin, G.L., Dong, J., Leonard, A., Fletcher, M. and Kaeberlein, M. 2016. Age-associated vulval integrity is an important marker of nematode healthspan. AGE 38: 419-31. doi: 10.1007/s11357-016-9936-8
Luc, M., Danold. P. and Taylor, C.N. 1979. On endotokia matricida and intra-uterine developement and hatching in nematodes. Nematology 25:268274. doi: 10.1163/187529279X00299
Luo, S., Kleemann, G.A., Ashraf, J.M., Shaw, W.M. and Murphy, C.T. 2010. TGF-? and insulin signaling regulate reproductive aging via oocyte and germline quality maintenance. Cell 143: 299-312. doi: 10.1016/j.cell.2010.09.013
McCarter, J., Bartlett, B., Dang, T., and Schedl, T. 1999. On the control of oocyte meiotic maturation and ovulation in Caenorhabditis elegans. Dev. Biol. 205: 111-128. doi: 10.1006/dbio.1996.8429
McGee, M.D., Weber, D., Day, N., Vitelli, C., Crippen, D., Herndon, L.A., Hall, D.H. and Melov, S. 2011. Loss of intestinal nuclei and intestinal integrity in aging C. elegans. Aging Cell 10: 699-710. doi: 10.1111/j.1474-9726.2011.00713.x, PDF
McGee, M.D., Day, N., Graham, J. and Melov, S. 2012. cep-1/p53-dependent dysplastic pathology of the aging C. elegans gonad. Aging 4: 256-69. doi: 10.18632/aging.100448, PDF
Pickett, C.L. and Kornfeld, K. 2013. Age-related degeneration of the egg-laying system promotes matricidal hatching in Caenorhabditis elegans. Aging Cell 12: 544-53. doi: 10.1111/acel.12079
Scharf, A., Pohl, F., Egan, B.M., Kocsisova, Z. and Kornfeld, K. 2021. Reproductive aging in Caenorhabditis elegans: From molecules to ecology. Front. Cell. Dev. Biol. 9: 718522 doi: 10.3389/fcell.2021.718522
Shi, C. and Murphy, C.T. 2014. Mating induces shrinking and death in Caenorhabditis mothers. Science 343: 536-40. doi: 10.1126/science.1242958
Starich, T.A., Hall, D.H. and Greenstein, D. 2014. Two classes of gap junction channels mediate soma-germline interactions essential for germline proliferation and gametogenesis in Caenorhabditis elegans. Genetics 198: 1127-53. doi: 10.1534/genetics.114.168815
Tolkin, T. and Hubbard, E.J.A. 2021. Germline stem and progenitor cell aging in C. elegans. Front. Cell. Dev. Biol. 9: 699671. doi: 10.3389/fcell.2021.699671
Toraason, E., Adler, V.L. and Libuda, D.E. 2022. Aging and sperm signals alter DNA break formation and repair in the C. elegans germline. PLoS Genet 18: e1010282. doi 10.1371/journal.pgen.1010282
Toth, M.L., Melentijevic, I., Shah, L., Bhatia, A., Lu, K., Talwar, A., Naji, H., Ibanez-Ventoso, C., Ghose, P., Jevince, A., Xue, J., Herndon, L.A., Bhanot, G., Rongo, C., Hall, D.H. and Driscoll, M. 2012. Neurite sprouting and synapse deterioration in the aging Caenorhabditis elegans nervous system. J. Neurosci. 32: 8778-90. doi: 10.1523/JNEUROSCI.1494-11.2012, PDF
Ward, S. and Carrel, J.S. 1979. Fertilization and sperm competition in the nematode Caenorhabditis elegans. Dev. Biol 73: 304-321. doi: 10.1016/0012-1606(79)90069-1
White, J.G., Southgate, E., Thomson, J.N. and Brenner, S. 1986. The structure of the nervous system of the nematode C. elegans. Philos. Trans. R. Soc. Lond. Series B. Biol. Sci. 314: 1-340. doi: 10.1098/rstb.1986.0056 - Article - PDF
* Description of Behavioral Classes (A, B, C) as described in Herndon et al., 2002
To characterize aging phenotypes, age-synchronized individual worms were scored both for spontaneous movement and for response to prodding with a wire over the course of their lifespan. Three distinct classes representing behavioral phenotypes were established. Animals that move constantly and make sinusoidal tracks were designated as class A. Class B animals mainly move when prodded. When they move it is with uncoordinated motion, leaving non-sinusoidal tracks. Class C animals do not move forward or backward, even upon prodding, but do show head and/or tail movement and twitch in response to touch. All animals begin adulthood in class A. Class B animals appear around days 6-7 of adulthood and class C around day 9-10 (at 20oC). At later ages, animals representing all classes can be found within the same population and it was found that the behavioral class type was the better predictor of life expectancy than chronological age (Herndon et al., 2002). Due to the stochastic nature of aging in an individual nematode, these classifications only reflect ongoing changes in nerve and muscle, while other tissues can show very different age-related effects within one behavioral class, declining faster or remaining healthy much longer.
This chapter should be cited as: Herndon, L.A., Wolkow, C.A. and Hall, D.H. 2023. The Aging Reproductive System. In WormAtlas. doi:10.3908/wormatlas.8.8
Edited for the web by Laura A. Herndon. Last revision: October 15, 2023.
Click pictures for new window with figure and legend, click again for high resolution image 
