Women's reproductive cessation is the earliest sign of human aging and is caused by decreasing oocyte quality. Similarly, C. elegans' reproduction declines in mid-adulthood and is caused by oocyte ...quality decline. Aberrant mitochondrial morphology is a hallmark of age-related dysfunction, but the role of mitochondrial morphology and dynamics in reproductive aging is unclear. We examined the requirements for mitochondrial fusion and fission in oocytes of both wild-type worms and the long-lived, long-reproducing insulin-like receptor mutant daf-2. We find that normal reproduction requires both fusion and fission, but that daf-2 mutants utilize a shift towards fission, but not fusion, to extend their reproductive span and oocyte health. daf-2 mutant oocytes' mitochondria are punctate (fissioned) and this morphology is primed for mitophagy, as loss of the mitophagy regulator PINK-1 shortens daf-2's reproductive span. daf-2 mutants maintain oocyte mitochondria quality with age at least in part through a shift toward punctate mitochondrial morphology and subsequent mitophagy. Supporting this model, Urolithin A, a metabolite that promotes mitophagy, extends reproductive span in wild-type mothers-even in mid-reproduction-by maintaining youthful oocytes with age. Our data suggest that promotion of mitophagy may be an effective strategy to maintain oocyte health with age.
Evolutionarily conserved signaling pathways are crucial for adjusting growth, reproduction, and cell maintenance in response to altered environmental conditions or energy balance. However, we have an ...incomplete understanding of the signaling networks and mechanistic changes that coordinate physiological changes across tissues. We found that loss of the cAMP response element-binding protein (CREB) transcription factor significantly slows Caenorhabditis elegans’ reproductive decline, an early hallmark of aging in many animals. Our results indicate that CREB acts downstream of the transforming growth factor β (TGF-β) Sma/Mab pathway in the hypodermis to control reproductive aging, and that it does so by regulating a Hedgehog-related signaling factor, WRT-10. Overexpression of hypodermal wrt-10 is sufficient to delay reproductive decline and oocyte quality deterioration, potentially acting via Patched-related receptors in the germline. This TGF-β-CREB-Hedgehog signaling axis allows a key metabolic tissue to communicate with the reproductive system to regulate oocyte quality and the rate of reproductive decline.
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•The transcription factor CREB regulates oocyte quality and reproductive decline•Hypodermal CREB downstream of TGF-β Sma/Mab signaling controls reproductive aging•CREB targets in the hypodermis include a Hedgehog-related signaling factor, wrt-10•WRT-10 delays reproductive aging, potentially via germline Patched receptors
Templeman et al. describe how the transcription factor CREB regulates reproductive aging. In the hypodermis, a Caenorhabditis elegans metabolic tissue, CREB acts downstream of TGF-β Sma/Mab signaling to control oocyte quality maintenance and the rate of reproductive decline. CREB exerts these effects via Hedgehog-related WRT-10 and germline Patched-related receptors.
Chromosome segregation during male meiosis is tailored to rapidly generate multitudes of sperm. Little is known about mechanisms that efficiently partition chromosomes to produce sperm. Using live ...imaging and tomographic reconstructions of spermatocyte meiotic spindles in
, we find the lagging X chromosome, a distinctive feature of anaphase I in
males, is due to lack of chromosome pairing. The unpaired chromosome remains tethered to centrosomes by lengthening kinetochore microtubules, which are under tension, suggesting that a 'tug of war' reliably resolves lagging. We find spermatocytes exhibit simultaneous pole-to-chromosome shortening (anaphase A) and pole-to-pole elongation (anaphase B). Electron tomography unexpectedly revealed spermatocyte anaphase A does not stem solely from kinetochore microtubule shortening. Instead, movement of autosomes is largely driven by distance change between chromosomes, microtubules, and centrosomes upon tension release during anaphase. Overall, we define novel features that segregate both lagging and paired chromosomes for optimal sperm production.
The potential to carry out high-throughput assays in a whole organism in a small space is one of the benefits of
, but worm assays often require a large sample size with frequent physical ...manipulations, rendering them highly labor-intensive. Microfluidic assays have been designed with specific questions in mind, such as analysis of behavior, embryonic development, lifespan, and motility. While these devices have many advantages, current technologies to automate worm experiments have several limitations that prevent widespread adoption, and most do not allow analyses of reproduction-linked traits. We developed a miniature
lab-on-a-chip device,
Lab, a reusable, multi-layer device with 200 separate incubation arenas that allows progeny removal, to automate a variety of worm assays on both individual and population levels.
Lab enables high-throughput simultaneous analysis of lifespan, reproductive span, and progeny production, refuting assumptions about the disposable soma hypothesis. Because
Lab chambers require small volumes, the chip is ideal for drug screens; we found that drugs previously shown to increase lifespan also increase reproductive span, and we discovered that low-dose metformin increases both.
Lab reduces the limitations of escaping and matricide that typically limit plate assays, revealing that feeding with heat-killed bacteria greatly extends lifespan and reproductive span of mated animals.
Lab allows tracking of life history traits of individuals, which revealed that the nutrient-sensing mTOR pathway mutant,
, reproduces nearly until its death. These findings would not have been possible to make in standard plate assays, in low-throughput assays, or in normal population assays.
Reproductive decline is one of the first systems to decline with age in women and has become increasingly important as the average maternal age increases. In this thesis work, I sought to 1) uncover ...novel regulators of reproductive aging, 2) investigate reproductive longevity mutants to reveal new mechanisms that promote reproductive longevity, and 3) identify therapeutics that slow reproductive decline.To achieve these goals, we have used the model organism C. elegans. C. elegans is an ideal model to study reproductive aging because it has a short generation time and many genetic tools. Importantly, key regulators of aging and longevity are conserved from worms to humans. Furthermore, work from our lab and others has established that, like women, worms spend at least half of their lifespans in a post-reproductive period; therefore, reproductive decline begins early in life. Also, the loss of oocyte quality with age, not the declining number of oocytes, governs reproductive decline, and genes that decline with age in oocytes are similar in worms, mice, and humans.In this thesis, I describe the following findings: 1) mitochondria are key regulators of reproductive longevity and rely on mitophagy to slow reproductive decline, 2) the mitophagy-promoting metabolite Urolithin A slows reproductive decline by improving oocyte quality, and 3) a novel mechanism that regulates the reproductive span requires communication between the hypodermis and the germline using Notch signaling. Further, we have designed and verified a microfluidic chip that simplifies and improves reproductive and lifespan assays and tracks healthspan metrics simultaneously on an individual worm level. Using this device, we have uncovered that 1) drugs and supplements that promote somatic longevity also promote reproductive longevity and 2) a novel role for conserved serum glucocorticoid-induced kinase 1(SGK-1) in reproductive span regulation. The findings reported here aim to have implications for humans and to further the research and interest in the reproductive aging field.
Animals face both external and internal dangers: pathogens threaten from the environment, and unstable genomic elements threaten from within. C. elegans protects itself from pathogens by “reading” ...bacterial small RNAs, using this information to both induce avoidance and transmit memories for four generations. Here, we found that memories can be transferred from either lysed animals or from conditioned media to naive animals via Cer1 retrotransposon-encoded virus-like particles. Moreover, Cer1 functions internally at the step of transmission of information from the germline to neurons and is required for learned avoidance. The presence of the Cer1 retrotransposon in wild C. elegans strains correlates with the ability to learn and inherit small-RNA-induced pathogen avoidance. Together, these results suggest that C. elegans has co-opted a potentially dangerous retrotransposon to instead protect itself and its progeny from a common pathogen through its inter-tissue signaling ability, hijacking this genomic element for its own adaptive immunity benefit.
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•Small-RNA-induced pathogen avoidance memory is transferred horizontally to naive animals•Horizontally acquired avoidance memory is inherited transgenerationally by progeny•Learned avoidance and horizontal memory transfer require the Cer1 retrotransposon•Cer1 expression in wild strains correlates with sRNA-induced pathogen avoidance
Cer1 retrotransposon particles mediate inter-tissue and inter-worm transfer of learned pathogen-avoidance behavior in Caenorhabditis elegans, providing an example of how a retrotransposon is used for a beneficial adaptive response in the host.
Reproductive ageing is one of the earliest human ageing phenotypes, and mitochondrial dysfunction has been linked to oocyte quality decline; however, it is not known which mitochondrial metabolic ...processes are critical for oocyte quality maintenance with age. To understand how mitochondrial processes contribute to Caenorhabditis elegans oocyte quality, we characterized the mitochondrial proteomes of young and aged wild-type and long-reproductive daf-2 mutants. Here we show that the mitochondrial proteomic profiles of young wild-type and daf-2 worms are similar and share upregulation of branched-chain amino acid (BCAA) metabolism pathway enzymes. Reduction of the BCAA catabolism enzyme BCAT-1 shortens reproduction, elevates mitochondrial reactive oxygen species levels, and shifts mitochondrial localization. Moreover, bcat-1 knockdown decreases oocyte quality in daf-2 worms and reduces reproductive capability, indicating the role of this pathway in the maintenance of oocyte quality with age. Notably, oocyte quality deterioration can be delayed, and reproduction can be extended in wild-type animals both by bcat-1 overexpression and by supplementing with vitamin B1, a cofactor needed for BCAA metabolism.
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