What Is Lost in the Weismann Barrier?

Acquired preferences for a novel food odor do not become stronger or stable after multiple generations of odor feeding in Bicyclus anynana butterfly larvae

Many herbivorous insects have specific host-plant preferences, and it is unclear how these preferences evolved. Previously, we found that Bicyclus anynana larvae can learn to prefer novel food odors from eating leaves with those odors and transmit those learned preferences to the next generation. It is uncertain whether such acquired odor preferences can increase across generations of repeated odor feeding and be maintained even in the absence of odor. In this study, we fed larvae with novel banana odor-coated leaves (odor-fed larvae) for five consecutive generations, without selection on behavioral choices, and measured how larval innate preferences changed over time. Then, we removed the odor stimulus from a larval subgroup, while the other group continued to be odor-fed. Our results show that larvae learned to prefer the novel odor within a generation of odor feeding and transmitted the learned preference to the next generation, as previously found. Odor-fed larvae preferred odor significantly more compared to control larvae across five generations of repeated odor or control feeding. However, this led neither to increased odor preference, nor its stabilization. This suggests that when butterfly larvae feed on a new host, a preference for that novel food plant may develop and be transmitted to the next generation, but this preference lasts for a single generation and disappears once the odor stimulus is removed.

Inheritance of Stress Responses via Small Non-Coding RNAs in Invertebrates and Mammals

While reports on the generational inheritance of a parental response to stress have been widely reported in animals, the molecular mechanisms behind this phenomenon have only recently emerged. The booming interest in epigenetic inheritance has been facilitated in part by the discovery that small non-coding RNAs are one of its principal conduits. Discovered 30 years ago in the Caenorhabditis elegans nematode, these small molecules have since cemented their critical roles in regulating virtually all aspects of eukaryotic development. Here, we provide an overview on the current understanding of epigenetic inheritance in animals, including mice and C. elegans, as it pertains to stresses such as temperature, nutritional, and pathogenic encounters. We focus on C. elegans to address the mechanistic complexity of how small RNAs target their cohort mRNAs to effect gene expression and how they govern the propagation or termination of generational perdurance in epigenetic inheritance. Presently, while a great amount has been learned regarding the heritability of gene expression states, many more questions remain unanswered and warrant further investigation.

Environmental and Genetic Traffic in the Journey from Sperm to Offspring

Recent advancements in the understanding of how sperm develop into offspring have shown complex interactions between environmental influences and genetic factors. The past decade, marked by a research surge, has not only highlighted the profound impact of paternal contributions on fertility and reproductive outcomes but also revolutionized our comprehension by unveiling how parental factors sculpt traits in successive generations through mechanisms that extend beyond traditional inheritance patterns. Studies have shown that offspring are more susceptible to environmental factors, especially during critical phases of growth. While these factors are broadly detrimental to health, their effects are especially acute during these periods. Moving beyond the immutable nature of the genome, the epigenetic profile of cells emerges as a dynamic architecture. This flexibility renders it susceptible to environmental disruptions. The primary objective of this review is to shed light on the diverse processes through which environmental agents affect male reproductive capacity. Additionally, it explores the consequences of paternal environmental interactions, demonstrating how interactions can reverberate in the offspring. It encompasses direct genetic changes as well as a broad spectrum of epigenetic adaptations. By consolidating current empirically supported research, it offers an exhaustive perspective on the interwoven trajectories of the environment, genetics, and epigenetics in the elaborate transition from sperm to offspring.

Agency in evolution of biomolecular communication

Biomolecular communication demands that interactions between parts of a molecular system act as scaffolds for message transmission. It also requires an organized system of signs-a communicative agency-for creating and transmitting meaning. The emergence of agency, the capacity to act in a given context and generate end-directed behaviors, has baffled evolutionary biologists for centuries. Here, I explore its emergence with knowledge grounded in over two decades of evolutionary genomic and bioinformatic exploration. Biphasic processes of growth and diversification exist that generate hierarchy and modularity in biological systems at widely ranging time scales. Similarly, a biphasic process exists in communication that constructs a message before it can be transmitted for interpretation. Transmission dissipates matter-energy and information and involves computation. Agency emerges when molecular machinery generates hierarchical layers of vocabularies in an entangled communication network clustered around the universal Turing machine of the ribosome. Computations canalize biological systems to perform biological functions in a dissipative quest to structure long-lived occurrents. This occurs within the confines of a "triangle of persistence" that maximizes invariance with trade-offs between economy, flexibility, and robustness. Thus, learning from previous historical and circumstantial experiences unifies modules in a hierarchy that expands the agency of systems.

Timeless or tainted? The effects of male ageing on seminal fluid

Reproductive ageing can occur due to the deterioration of both the soma and germline. In males, it has mostly been studied with respect to age-related changes in sperm. However, the somatic component of the ejaculate, seminal fluid, is also essential for maintaining reproductive function. Whilst we know that seminal fluid proteins (SFPs) are required for male reproductive success across diverse taxa, age-related changes in SFP quantity and composition are little understood. Additionally, only few studies have explored the reproductive ageing of the tissues that produce SFPs, and the resulting reproductive outcomes. Here we provide a systematic review of studies addressing how advancing male age affects the production and properties of seminal fluid, in particular SFPs and oxidative stress, highlighting many open questions and generating new hypotheses for further research. We additionally discuss how declines in function of different components of seminal fluid, such as SFPs and antioxidants, could contribute to age-related loss of reproductive ability. Overall, we find evidence that ageing results in increased oxidative stress in seminal fluid and a decrease in the abundance of various SFPs. These results suggest that seminal fluid contributes towards important age-related changes influencing male reproduction. Thus, it is essential to study this mostly ignored component of the ejaculate to understand male reproductive ageing, and its consequences for sexual selection and paternal age effects on offspring.

Food abundance in men before puberty predicts a range of cancers in grandsons

Nutritional conditions early in human life may influence phenotypic characteristics in later generations. A male-line transgenerational pathway, triggered by the early environment, has been postulated with support from animal and a small number of human studies. Here we analyse individuals born in Uppsala Sweden 1915-29 with linked data from their children and parents, which enables us to explore the hypothesis that pre-pubertal food abundance may trigger a transgenerational effect on cancer events. We used cancer registry and cause-of-death data to analyse 3422 cancer events in grandchildren (G2) by grandparental (G0) food access. We show that variation in harvests and food access in G0 predicts cancer occurrence in G2 in a specific way: abundance among paternal grandfathers, but not any other grandparent, predicts cancer occurrence in grandsons but not in granddaughters. This male-line response is observed for several groups of cancers, suggesting a general susceptibility, possibly acquired in early embryonic development. We observed no transgenerational influence in the middle generation.

Beyond Genes: Germline Disruption in the Etiology of Autism Spectrum Disorders

Investigations into the etiology of autism spectrum disorders have been largely confined to two realms: variations in DNA sequence and somatic developmental exposures. Here we suggest a third route-disruption of the germline epigenome induced by exogenous toxicants during a parent's gamete development. Similar to cases of germline mutation, these molecular perturbations may produce dysregulated transcription of brain-related genes during fetal and early development, resulting in abnormal neurobehavioral phenotypes in offspring. Many types of exposures may have these impacts, and here we discuss examples of anesthetic gases, tobacco components, synthetic steroids, and valproic acid. Alterations in parental germline could help explain some unsolved phenomena of autism, including increased prevalence, missing heritability, skewed sex ratio, and heterogeneity of neurobiology and behavior.

Inheritance of somatic mutations by animal offspring

Since 1892, it has been widely assumed that somatic mutations are evolutionarily irrelevant in animals because they cannot be inherited by offspring. However, some nonbilaterians segregate the soma and germline late in development or never, leaving the evolutionary fate of their somatic mutations unknown. By investigating uni- and biparental reproduction in the coral Acropora palmata (Cnidaria, Anthozoa), we found that uniparental, meiotic offspring harbored 50% of the 268 somatic mutations present in their parent. Thus, somatic mutations accumulated in adult coral animals, entered the germline, and were passed on to swimming larvae that grew into healthy juvenile corals. In this way, somatic mutations can increase allelic diversity and facilitate adaptation across habitats and generations in animals.

Challenging dogmas: How transgenerational epigenetics reshapes our views on life

The emergence of the field of transgenerational epigenetics inheritance (TEI) has profoundly reshaped our understanding of the relationships between environment, soma, and germ cells as well as of heredity. TEI refers to the changes in chromatin state, gene expression, and/or phenotypes that are transmitted across several generations without involving changes to the DNA sequences. TEI has direct connections with, and feeds from, the fields of molecular biology, genetics, developmental biology, and reproductive biology, among others. However, the expansion of TEI-related research, has profoundly reshaped boundaries within each field and often led to the erosion of theories and concepts considered as tenets of biology. We first explore how the molecularization of biology has shifted the definition of epigenetics to include the notion of heredity and how epigenetics has refined our understanding of the central dogma of biology. The demonstrated transfer of environmental information from soma to germ cell through extracellular vesicles and subsequent alteration of health outcomes in offspring has put a definite end to the long-held principle of the Weismann barrier. TEI has also simultaneously led to the revival of the inheritance of acquired characteristics while further eroding the concept of an epigenetic "blank slate" in mammals. Using an historical framework, and via the exploration of central studies in the field, in this perspective article, we will draw a compelling argument for the revolutionary aspect of TEI in biology.

Meiosis initiation: a story of two sexes in all creatures great and small

Meiosis facilitates diversity across individuals and serves as a major driver of evolution. However, understanding how meiosis begins is complicated by fundamental differences that exist between sexes and species. Fundamental meiotic research is further hampered by a current lack of human meiotic cells lines. Consequently, much of what we know relies on data from model organisms. However, contextualising findings from yeast, worms, flies and mice can be challenging, due to marked differences in both nomenclature and the relative timing of meiosis. In this review, we set out to combine current knowledge of signalling and transcriptional pathways that control meiosis initiation across the sexes in a variety of organisms. Furthermore, we highlight the emerging links between meiosis initiation and oncogenesis, which might explain the frequent re-expression of normally silent meiotic genes in a variety of human cancers.

How Family Histories Can Inform Research About Germ Cell Exposures: The Example of Autism

Throughout the scientific literature, heritable traits are routinely presumed to be genetic in origin. However, as emerging evidence from the realms of genetic toxicology and epigenomics demonstrate, heritability may be better understood as encompassing not only DNA sequence passed down through generations, but also disruptions to the parental germ cells causing de novo mutations or epigenetic alterations, with subsequent shifts in gene expression and functions in offspring. The Beyond Genes conference highlighted advances in understanding these aspects at molecular, experimental and epidemiological levels. In this commentary I suggest that future research on this topic could be inspired by collecting parents' germ cell exposure histories, with particular attention to cases of families with multiple children suffering idiopathic disorders. In so doing I focus on the endpoint of autism spectrum disorders (ASD). Rates of this serious neurodevelopment disability have climbed around the world, a growing crisis that cannot be explained by diagnostic shifts. ASD's strong heritability has prompted a research program largely focused on DNA sequencing to locate rare and common variants, but decades of this gene-focused research have revealed surprisingly little about the molecular origins of the disorder. Based on my experience as the mother of two children with idiopathic autism, and as a research philanthropist and autism advocate, I suggest ways researchers might probe parental germ cell exposure histories to develop new hypotheses that may ultimately reveal sources of non-genetic heritability in a subset of idiopathic heritable pathologies.