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Maternal effects in the model system Daphnia: the ecological past meets the epigenetic future
Maternal effects have been shown to play influential roles in many evolutionary and ecological processes. However, understanding how environmental stimuli induce within-generation responses that transverse across generations remains elusive, particularly when attempting to segregate confounding effects from offspring genotypes. This review synthesizes literature regarding resource- and predation-driven maternal effects in the model system Daphnia, detailing how the maternal generation responds to the environmental stimuli and the maternal effects seen in the offspring generation(s). Our goal is to demonstrate the value of Daphnia as a model system by showing how general principles of maternal effects emerge from studies on this system. By integrating the results across different types of biotic drivers of maternal effects, we identified broadly applicable shared characteristics: 1. Many, but not all, maternal effects involve offspring size, influencing resistance to starvation, infection, predation, and toxins. 2. Maternal effects manifest more strongly when the offspring’s environment is poor. 3. Strong within-generation responses are typically associated with strong across-generation responses. 4. The timing of the maternal stress matters and can raise or lower the magnitude of the effect on the offspring’s phenotype. 5. Embryonic exposure effects could be mistaken for maternal effects. We outline questions to prioritize for future research and discuss the possibilities for integration of ecologically relevant studies of maternal effects in natural populations with the molecular mechanisms that make them possible, specifically by addressing genetic variation and incorporating information on epigenetics. These small crustaceans can unravel how and why non-genetic information gets passed to future generations.
Paternal heroin self-administration in rats increases drug-seeking behavior in male offspring via miR-19b downregulation in the nucleus accumbens
Accumulating evidence indicates that drug addiction may lead to adaptive behavioral changes in offspring, potentially due to epigenetic modifications in parental germline. However, the underlying mechanisms remain inadequately understood. In this study, we show that paternal heroin self-administration (SA) increased heroin-seeking behavior in the F1 generation, when compared with offspring sired by yoke-infused control males, indicating cross-generational impact of paternal voluntary heroin seeking behavior. Notably, the increase of heroin seeking behavior in offspring was replicated by zygotic microinjection of sperm RNAs derived from sperm of heroin-SA-experienced rats. Analysis of non-coding RNAs in spermatozoa revealed coordinated changes in miRNA content between the nucleus accumbens and spermatozoa. We validated that restoration of miR-19b downregulation in sperm RNA from self-administration-experienced rats, in parallel with its overexpression in the nucleus accumbens of F1 offspring sired by heroin-SA-experienced fathers, reversed the increased heroin SA observed in these F1 offspring. Taken together, our findings suggest in rats that paternal heroin self-administration induces epigenetic changes in both brain and sperm miRNA, with miR-19b downregulation playing a critical role in mediating the epigenetic inheritance of increased heroin self-administration behavior in the F1 generation.
Transgenerational inheritance of diabetes susceptibility in male offspring with maternal androgen exposure
Androgen exposure (AE) poses a profound health threat to women, yet its transgenerational impacts on male descendants remain unclear. Here, employing a large-scale mother-child cohort, we show that maternal hyperandrogenism predisposes sons to β-cell dysfunction. Male offspring mice with prenatal AE exhibited hyperglycemia and glucose intolerance across three generations, which were further exacerbated by aging and a high-fat diet. Mechanistically, compromised insulin secretion underlies this transgenerational susceptibility to diabetes. Integrated analyses of methylome and transcriptome revealed differential DNA methylation of β-cell functional genes in AE-F1 sperm, which was transmitted to AE-F2 islets and further retained in AE-F2 sperm, leading to reduced expression of genes related to insulin secretion, including Pdx1, Irs1, Ptprn2, and Cacna1c. The methylation signatures in AE-F1 sperm were corroborated in diabetic humans and the blood of sons with maternal hyperandrogenism. Moreover, caloric restriction and metformin treatments normalized hyperglycemia in AE-F1 males and blocked their inheritance to offspring by restoring the aberrant sperm DNA methylations. Our findings highlight the transgenerational inheritance of impaired glucose homeostasis in male offspring from maternal AE via DNA methylation changes, providing methylation biomarkers and therapeutic strategies to safeguard future generations’ metabolic health.
A torpor-like state in mice slows blood epigenetic aging and prolongs healthspan
Torpor and hibernation are extreme physiological adaptations of homeotherms associated with pro-longevity effects. Yet the underlying mechanisms of how torpor affects aging, and whether hypothermic and hypometabolic states can be induced to slow aging and increase healthspan, remain unknown. Here we demonstrate that the activity of a spatially defined neuronal population in the preoptic area, which has previously been identified as a torpor-regulating brain region, is sufficient to induce a torpor-like state (TLS) in mice. Prolonged induction of TLS slows epigenetic aging across multiple tissues and improves healthspan. We isolate the effects of decreased metabolic rate, long-term caloric restriction, and decreased core body temperature (Tb) on blood epigenetic aging and find that the decelerating effect of TLSs on aging is mediated by decreased Tb. Taken together, our findings provide novel mechanistic insight into the decelerating effects of torpor and hibernation on aging and support the growing body of evidence that Tb is an important mediator of the aging processes.
Gestational autoantibody exposure impacts early brain development in a rat model of MAR autism
Maternal autoantibody-related autism (MARA) is a subtype of autism characterized by the maternal production of specific patterns of autoantibodies during pregnancy, which significantly increases the likelihood of an autism diagnosis in their children. Multiple patterns of MARA autoantibodies (MARA-ABS) have been identified, and differences in the severity of the autism phenotype associated with each autoantibody pattern have been described. In this study, we utilized preclinical rat models to further elucidate the differential effects of MARA-AB exposure based on the known clinical patterns, including the originally reported pattern of lactate dehydrogenase A and B (LDHA/B) + collapsin response mediator protein 1 (CRMP1) + stress-induced phosphoprotein 1 (STIP1), as well as the more recently described patterns of CRMP1+CRMP2, CRMP1 + guanine deaminase (GDA), and STIP1+ neuron-specific enolase (NSE). We induced endogenous MARA-AB production in rat dams before pregnancy to expose offspring to the ABs throughout gestation. We found that in postnatal day 2 offspring exposed to MARA-ABS, the levels of brain and serum cytokines/chemokines/growth factors were altered based on the pattern of MARA-AB exposure. Further, bulk transcriptomic profiles of coronal sections containing hippocampal formation and the adjacent cortical and subcortical structures suggested changes in cellular proliferation and differentiation following MARA exposure. These combined observations demonstrate that gestational exposure to MARA-ABS alters early gene expression and immune signaling molecules, both of which may contribute to the altered neurodevelopment and behaviors associated with MARA.
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