[Evolution of cancer resistance in the animal kingdom]. / Évolution de la résistance au cancer dans le monde animal.

Cancer is an inevitable collateral problem inherent in the evolution of multicellular organisms, which appeared at the end of the Precambrian. Faced to this constraint, a range of diverse anticancer defenses has evolved across the animal kingdom. Today, investigating how animal organisms, especially those of large size and long lifespan, manage cancer-related issues has both fundamental and applied outcomes, as it could inspire strategies for preventing or treating human cancers. In this article, we begin by presenting the conceptual framework for understanding evolutionary theories regarding the development of anti-cancer defenses. We then present a number of examples that have been extensively studied in recent years, including naked mole rats, elephants, whales, placozoa, xenarthras (such as sloths, armadillos and anteaters) and bats. The contributions of comparative genomics to understanding evolutionary convergences are also discussed. Finally, we emphasize that natural selection has also favored anti-cancer adaptations aimed at avoiding mutagenic environments, for example by maximizing immediate reproductive efforts in the event of cancer. Exploring these adaptive solutions holds promise for identifying novel approaches to improve human health.

Title: Évolution de la résistance au cancer dans le monde animal. Abstract: Le cancer est un dommage collatéral inévitable inhérent à l'évolution des organismes multicellulaires, apparus à la fin du Précambrien. L'exploration de la manière dont les animaux, en particulier ceux de grande taille et de longue durée de vie, font face au cancer, comporte des enjeux à la fois fondamentaux et appliqués. Dans cet article, nous commençons par présenter le cadre conceptuel nécessaire pour comprendre les théories qui traitent de l'évolution des défenses anti-cancéreuses. Nous présentons ensuite un certain nombre d'exemples, notamment les rats-taupes nus, les éléphants, les baleines, les xénarthres (paresseux, tatous et fourmiliers), les chauves-souris et les placozoaires1. Les contributions de la génomique comparative à la compréhension des convergences évolutives sont également abordées. Enfin, nous indiquons que la sélection naturelle a également favorisé des adaptations visant à éviter les zones mutagènes, par exemple, ou à maximiser l'effort de reproduction immédiat en cas de cancer. L'exploration de ces solutions, intéressante conceptuellement, pourrait aussi permettre d'envisager de nouvelles approches thérapeutiques pour la santé humaine.

Immunostimulation of Asian elephant (Elephas maximus) blood cells by parapoxvirus ovis and CpG motif-containing bacterial plasmid DNA upregulates innate immune gene expression.

The immune system of Asian elephants (Elephas maximus) is poorly studied, compared to that of livestock, rodents or humans. The innate immune response has become a focus of interest in relation to Elephant endotheliotropic herpesviruses (EEHVs). EEHVs cause a fatal hemorrhagic disease (EEHV-HD) and are a significant threat to captive Asian elephant populations worldwide. Similar to other herpesvirus infections, nearly all animals become infected, but only some develop disease. As progression to EEHV-HD is often acute, a robust innate immune response is crucial to control EEHV infections. This is invariably true of the host in the first instance, but it can also potentially be modulated by intervention strategies. Here, two immunostimulant veterinary medicinal products, authorized for use in domestic species, were tested for their ability to induce innate anti-viral immune responses in Asian elephant blood cells. Sequence data were obtained for a range of previously unidentified Asian elephant immune genes, including C-X-C motif chemokine ligand 10 (CXCL10), interferon stimulated gene 15 (ISG15) and myxovirus GTPase 1 (Mx1), and were employed in the design of species-specific qPCR assays. These assays were subsequently used in analyses to determine fold changes in gene expression over a period of 24 hours. This study demonstrates that both immunostimulant medications are capable of inducing significant innate anti-viral immune responses which suggests that both could be beneficial in controlling EEHV infections in Asian elephants.

Meiosis: The silk moth and the elephant.

In most eukaryotes, balanced chromosome segregation at meiosis requires crossovers, but female Bombyx mori lack these structures. Instead, the synaptonemal complex is repurposed to compensate for this absence of crossovers, a remarkable example of exaptation.

African and Asian elephant ivory discrimination using a portable strip test.

Currently, the global elephant population has significantly declined due to the poaching of elephants for their ivory, and this is the reason why elephants are listed in the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). However, Thailand allows the legal trade of ivory from registered, domesticated Asian elephants, leading to the smuggling of African elephant ivory, and passing them off as Asian elephant ivory. Therefore, this research aims to develop and validate a portable strip test to discriminate between Asian and African elephants DNA, using Recombinase Polymerase Amplification (RPA) and Lateral Flow Dipstick assay (LFD) according to international standards. The results showed that the strip test can be successfully developed with 100% accuracy (n = 105). This kit is specific to elephants, has a detection limit of 0.125 ng of DNA, and can effectively discriminate a variety of elephant ivory, including raw ivory, ivory products, and aged ivory over 25 years old, which had been damaged by fire, all with 100% accuracy (n = 117). Additionally, the developed strip test is designed to be portable and cost-effective. It does not require expensive laboratory equipment and provides a faster analysis process compared with conventional PCR-based methods. This will expedite the legal process and enforcement of laws related to elephant conservation, reducing the opportunities for illegal activities, and enabling timely prosecution under relevant wildlife conservation laws in Thailand and internationally.

Haplotype-resolved chromosome-scale genomes of the Asian and African Savannah Elephants.

The Proboscidea, which includes modern elephants, were once the largest terrestrial animals among extant species. They suffered mass extinction during the Ice Age. As a unique branch on the evolutionary tree, the Proboscidea are of great significance for the study of living animals. In this study, we generate chromosome-scale and haplotype-resolved genome assemblies for two extant Proboscidea species (Asian Elephant, Elephas maximus and African Savannah Elephant, Loxodonta africana) using Pacbio, Hi-C, and DNBSEQ technologies. The assembled genome sizes of the Asian and African Savannah Elephant are 3.38 Gb and 3.31 Gb, with scaffold N50 values of 130 Mb and 122 Mb, respectively. Using Hi-C technology ~97% of the scaffolds are anchored to 29 pseudochromosomes. Additionally, we identify ~9 Mb Y-linked sequences for each species. The high-quality genome assemblies in this study provide a valuable resource for future research on ecology, evolution, biology and conservation of Proboscidea species.

From Churchill to Elephants: The Role of Protective Genes against Cancer.

Richard Peto's paradox, first described in 1975 from an epidemiological perspective, established an inverse correlation between the probability of developing cancer in multicellular organisms and the number of cells. Larger animals exhibit fewer tumors compared to smaller ones, though exceptions exist. Mice are more susceptible to cancer than humans, while elephants and whales demonstrate significantly lower cancer prevalence rates than humans. How nature and evolution have addressed the issue of cancer in the animal kingdom remains largely unexplored. In the field of medicine, much attention has been devoted to cancer-predisposing genes, as they offer avenues for intervention, including blocking, downregulating, early diagnosis, and targeted treatment. Predisposing genes also tend to manifest clinically earlier and more aggressively, making them easier to identify. However, despite significant strides in modern medicine, the role of protective genes lags behind. Identifying genes with a mild predisposing effect poses a significant challenge. Consequently, comprehending the protective function conferred by genes becomes even more elusive, and their very existence is subject to questioning. While the role of variable expressivity and penetrance defects of the same variant in a family is well-documented for many hereditary cancer syndromes, attempts to delineate the function of protective/modifier alleles have been restricted to a few instances. In this review, we endeavor to elucidate the role of protective genes observed in the animal kingdom, within certain genetic syndromes that appear to act as cancer-resistant/repressor alleles. Additionally, we explore the role of protective alleles in conditions predisposing to cancer. The ultimate goal is to discern why individuals, like Winston Churchill, managed to live up to 91 years of age, despite engaging in minimal physical activity, consuming large quantities of alcohol daily, and not abstaining from smoking.

Mitochondrial genome sequence comparisons indicate that the elephant louse Haematomyzus elephantis (Piaget, 1869) contains cryptic species.

The parvorder Rhynchopthirina contains three currently recognised species of lice that parasitize elephants (both African savanna elephant Loxodonta africana and Asian elephant Elephas maximus), desert warthogs (Phacochoerus aethiopicus) and Red River hogs (Potamochoerus porcus), respectively. The Asian elephant lice and the African savanna elephant lice are currently treated as the same species, Haematomyzus elephantis (Piaget, 1869), based on morphology despite the fact that their hosts diverged 8.4 million years ago. In the current study, we sequenced 23 mitochondrial (mt) genes of African savanna elephant lice collected in South Africa and analysed the sequence divergence between African savanna elephant lice and previously sequenced Asian elephant lice. Sequence comparisons revealed >23% divergence for the 23 mt genes as a whole and ~17% divergence for cox1 gene between African savanna and Asian elephant lice, which were far higher than the divergence expected within a species. Furthermore, the mt gene sequence divergences between these lice are 3.76-4.6 times higher than that between their hosts, the African savanna and Asian elephants, which are expected for the co-divergence and co-evolution between lice and their elephant hosts. We conclude that (1) H. elephantis (Piaget, 1869) contains cryptic species and (2) African savanna and Asian elephant lice are different species genetically that may have co-diverged and co-evolved with their hosts.

Age estimation of captive Asian elephants (Elephas maximus) based on DNA methylation: An exploratory analysis using methylation-sensitive high-resolution melting (MS-HRM).

Age is an important parameter for bettering the understanding of biodemographic trends-development, survival, reproduction and environmental effects-critical for conservation. However, current age estimation methods are challenging to apply to many species, and no standardised technique has been adopted yet. This study examined the potential use of methylation-sensitive high-resolution melting (MS-HRM), a labour-, time-, and cost-effective method to estimate chronological age from DNA methylation in Asian elephants (Elephas maximus). The objective of this study was to investigate the accuracy and validation of MS-HRM use for age determination in long-lived species, such as Asian elephants. The average lifespan of Asian elephants is between 50-70 years but some have been known to survive for more than 80 years. DNA was extracted from 53 blood samples of captive Asian elephants across 11 zoos in Japan, with known ages ranging from a few months to 65 years. Methylation rates of two candidate age-related epigenetic genes, RALYL and TET2, were significantly correlated with chronological age. Finally, we established a linear, unisex age estimation model with a mean absolute error (MAE) of 7.36 years. This exploratory study suggests an avenue to further explore MS-HRM as an alternative method to estimate the chronological age of Asian elephants.

Chromosome-level Asian elephant genome assembly and comparative genomics of long-lived mammals reveal the common substitutions for cancer resistance.

The naked mole rat (Heterocephalus glaber), bats (e.g., genus Myotis), and elephants (family Elephantidae) are known as long-lived mammals and are assumed to be excellent cancer antagonists. However, whether there are common genetic changes underpinning cancer resistance in these long-lived species is yet to be fully established. Here, we newly generated a high-quality chromosome-level Asian elephant (Elephas maximus) genome and identified that the expanded gene families in elephants are involved in Ras-associated and base excision repair pathways. Moreover, we performed comparative genomic analyses of 12 mammals and examined genes with signatures of positive selection in elephants, naked mole rat, and greater horseshoe bat. Residues at positively selected sites of CDR2L and ALDH6A1 in these long-lived mammals enhanced the inhibition of tumor cell migration compared to those in short-lived relatives. Overall, our study provides a new genome resource and a preliminary survey of common genetic changes in long-lived mammals.

Mechanism of inulin in colic and gut microbiota of captive Asian elephant.

BACKGROUND: Gut microbiota have a complex role on the survivability, digestive physiology, production, and growth performance in animals. Recent studies have emphasized the effects of prebiotics therapy on the gut disease, but the relationship between elephant gut-related diseases and prebiotics remains elusive. Here, a case study was undertaken to evaluate the mechanism of inulin treatment in colic in Asian elephant (Elephas maximus Linnaeus). METHODS: Fecal samples were collected from a sick elephant and four healthy elephants. Analysis of microbial profile was carried out by 16S rRNA sequencing, and the short chain fatty acids were tested by gas chromatography. The physiological function of "inulin-microbiota" of elephant was verified in mice by fecal microbial transplantation (FMT). The expression of related proteins was determined by Western blotting and qPCR. RESULTS: (1) Eating inulin can cure gut colic of the sick elephant and changed gut microbiota. (2) It was found that "inulin microbiota" from the post-treatment elephants can promote the proliferation of intestinal cells, increase the utilization of short chain fatty acids (SCFAs), maintain intestinal barrier, and reduce the inflammation in mice. (3) The mechanism was inulin-gut microbiota-SCFAs-immune barrier. CONCLUSIONS: Inulin contributed to rehabilitate the gut microbiota and gut immune barrier of the elephant with colic. This provides reasonable verification for using prebiotics to treat the colic in captive elephants. Prebiotics will foresure play an increasingly important role in disease prevention and treatment of captive animals in the future. Video Abstract.

A genetic glimpse of the Chinese straight-tusked elephants.

Straight-tusked elephants (genus: Palaeoloxodon) including their island dwarf forms are extinct enigmatic members of the Pleistocene megafauna and the most common Pleistocene elephants after the mammoths. Their taxonomic placement has been revised several times. Using palaeogenomic evidence, previous studies suggested that the European P. antiquus has a hybrid origin, but no molecular data have been retrieved from their Asian counterparts, leaving a gap in our knowledge of the global phylogeography and population dynamics of Palaeoloxodon. Here, we captured a high-quality complete mitogenome from a Pleistocene Elephantidae molar (CADG841) from Northern China, which was previously morphologically assigned to the genus Elephas (Asian elephant), and partial mitochondrial sequences (838 bp) of another Palaeoloxodon sp. specimen (CADG1074) from Northeastern China. We found that both Chinese specimens cluster with a 244 000-year-old P. antiquus (specimen name: WE) from Western Europe, suggesting that this clade may represent a population with a large spatial span across Eurasia. Based on the fossil record and the molecular dating of both the divergences of different Palaeoloxodon mitochondrial clades and previously determined hybridization events, we propose that this Eurasian-wide WE clade provides evidence for an earlier migration and/or another hybridization event that happened in the evolutionary history of straight-tusked elephants.

Genetic features of Sri Lankan elephant, Elephas maximus maximus Linnaeus revealed by high throughput sequencing of mitogenome and ddRAD-seq.

Elephas maximus maximus Linnaeus, the Sri Lankan subspecies is the largest and the darkest among Asian elephants. Patches of depigmented areas with no skin color on the ears, face, trunk, and belly morphologically differentiate it from the others. The elephant population in Sri Lanka is now limited to smaller areas and protected under Sri Lankan law. Despite its ecological and evolutionary importance, the relationship between Sri Lankan elephants and their phylogenetic position among Asian elephants remains controversial. While identifying genetic diversity is the key to any conservation and management strategies, limited data is currently available. To address such issues, we analyzed 24 elephants with known parental lineages with high throughput ddRAD-seq. The mitogenome suggested the coalescence time of the Sri Lankan elephant at ~0.2 million years, and sister to Myanmar elephants supporting the hypothesis of the movement of elephants in Eurasia. The ddRAD-seq approach identified 50,490 genome-wide SNPs among Sri Lankan elephants. The genetic diversity within Sri Lankan elephants assessed with identified SNPs suggests a geographical differentiation resulting in three main clusters; north-eastern, mid-latitude, and southern regions. Interestingly, though it was believed that elephants from the Sinharaja rainforest are of an isolated population, the ddRAD-based genetic analysis clustered it with the north-eastern elephants. The effect of habitat fragmentation on genetic diversity could be further assessed with more samples with specific SNPs identified in the current study.

Uncoupling elephant TP53 and cancer.

Elephant testicles do not descend, with implications for sperm production being hot enough to compromise germline DNA replication/repair. Uniquely, elephants also possess 20 copies of a gene encoding for the p53 protein. Did elephants evolve multiplication of the TP53 gene complex to protect their germline rather than to fight cancer?

What distinguishes the elephant from E. coli: Causal spreading and the biological principles of metazoan complexity.

Jacques Monod famously said that 'What is true for E. coli is true for the elephant.' While this might be correct in the basic sense that both use nucleic acids and proteins, it is no longer clear that they use them in quite the same way. The many qualitative differences in the biomolecular constitution and mechanisms of protozoans and metazoans, from the proportions of non-coding DNA to those of multidomain and disordered proteins and the mechanisms of gene regulation, seem to reflect different generic principles in how the two types of organism operate at the molecular and cellular levels. Here I suggest that one way to think about those differences is as a shift in the locus of biological causation - a shift that has implications for making biomedical interventions in humans.

Genomic resources for Asian (Elephas maximus) and African savannah elephant (Loxodonta africana) conservation and health research.

We provide novel genomic resources to help understand the genomic traits involved in elephant health and to aid conservation efforts. We sequence 11 elephant genomes (5 African savannah, 6 Asian) from North American zoos, including 9 de novo assemblies. We estimate elephant germline mutation rates and reconstruct demographic histories. Finally, we provide an in-solution capture assay to genotype Asian elephants. This assay is suitable for analyzing degraded museum and noninvasive samples, such as feces and hair. The elephant genomic resources we present here should allow for more detailed and uniform studies in the future to aid elephant conservation efforts and disease research.

Elephants as an animal model for self-domestication.

Humans are unique in their sophisticated culture and societal structures, their complex languages, and their extensive tool use. According to the human self-domestication hypothesis, this unique set of traits may be the result of an evolutionary process of self-induced domestication, in which humans evolved to be less aggressive and more cooperative. However, the only other species that has been argued to be self-domesticated besides humans so far is bonobos, resulting in a narrow scope for investigating this theory limited to the primate order. Here, we propose an animal model for studying self-domestication: the elephant. First, we support our hypothesis with an extensive cross-species comparison, which suggests that elephants indeed exhibit many of the features associated with self-domestication (e.g., reduced aggression, increased prosociality, extended juvenile period, increased playfulness, socially regulated cortisol levels, and complex vocal behavior). Next, we present genetic evidence to reinforce our proposal, showing that genes positively selected in elephants are enriched in pathways associated with domestication traits and include several candidate genes previously associated with domestication. We also discuss several explanations for what may have triggered a self-domestication process in the elephant lineage. Our findings support the idea that elephants, like humans and bonobos, may be self-domesticated. Since the most recent common ancestor of humans and elephants is likely the most recent common ancestor of all placental mammals, our findings have important implications for convergent evolution beyond the primate taxa, and constitute an important advance toward understanding how and why self-domestication shaped humans' unique cultural niche.

Gut Microbiome Variation Along A Lifestyle Gradient Reveals Threats Faced by Asian Elephants.

The gut microbiome is closely related to host nutrition and health. However, the relationships between gut microorganisms and host lifestyle are not well characterized. In the absence of confounding geographic variation, we defined clear patterns of variation in the gut microbiomes of Asian elephants (AEs) in the Wild Elephant Valley, Xishuangbanna, China, along a lifestyle gradient (completely captive, semicaptive, semiwild, and completely wild). A phylogenetic analysis using the 16S rRNA gene sequences highlighted that the microbial diversity decreased as the degree of captivity increased. Furthermore, the results showed that the bacterial taxon WCHB1-41_c was substantially affected by lifestyle variations. qRT-PCR analysis revealed a paucity of genes related to butyrate production in the gut microbiome of AEs with a completely wild lifestyle, which may be due to the increased unfavorable environmental factors. Overall, these results demonstrate the distinct gut microbiome characteristics among AEs with a gradient of lifestyles and provide a basis for designing strategies to improve the well-being or conservation of this important animal species.

In vitro and in vivo development of interspecies Asian elephant embryos reconstructed with pig enucleated oocytes.

Interspecies somatic cell nuclear transfer (iSCNT) has an immense potential to rescue endangered animals and extinct species like mammoths. In this study, we successfully established an Asian elephant's fibroblast cell lines from ear tissues, performed iSCNT with porcine oocytes and evaluated the in vitro and in vivo development of reconstructed embryos. A total of 7780 elephant-pig iSCNT embryos were successfully reconstructed and showed in vitro development with cleavage rate, 4-cell, 8-cell and blastocyst rate of 73.01, 30.48, 5.64, and 4.73%, respectively. The total number of elephant-pig blastocyte cells and diameter of hatched blastocyte was 38.67 and 252.75 µm, respectively. Next, we designed species-specific markers targeting EDNRB, AGRP and TYR genes to verify the genome of reconstructed embryos with donor nucleus/species. The results indicated that 53.2, 60.8, and 60.8% of reconstructed embryos (n = 235) contained elephant genome at 1-cell, 2-cell and 4-cell stages, respectively. However, the percentages decreased to 32.3 and 32.7% at 8-cell and blastocyst stages, respectively. Furthermore, we also evaluated the in vivo development of elephant-pig iSCNT cloned embryos and transferred 2260 reconstructed embryos into two surrogate gilts that successfully became pregnant and a total of 11 (1 and 10) fetuses were surgically recovered after 17 and 19 days of gestation, respectively. The crown-rump length and width of elephant-pig cloned fetuses were smaller than the control group. Unfortunately, none of these fetuses contained elephant genomes, which suggested that elephant embryos failed to develop in vivo. In conclusion, we successfully obtained elephant-pig reconstructed embryos for the first time and these embryos are able to develop to blastocyst, but the in vivo developmental failure needs further investigated.

Parallel evolution of reduced cancer risk and tumor suppressor duplications in Xenarthra.

The risk of developing cancer is correlated with body size and lifespan within species, but there is no correlation between cancer and either body size or lifespan between species indicating that large, long-lived species have evolved enhanced cancer protection mechanisms. Previously we showed that several large bodied Afrotherian lineages evolved reduced intrinsic cancer risk, particularly elephants and their extinct relatives (Proboscideans), coincident with pervasive duplication of tumor suppressor genes (Vazquez and Lynch, 2021). Unexpectedly, we also found that Xenarthrans (sloths, armadillos, and anteaters) evolved very low intrinsic cancer risk. Here, we show that: (1) several Xenarthran lineages independently evolved large bodies, long lifespans, and reduced intrinsic cancer risk; (2) the reduced cancer risk in the stem lineages of Xenarthra and Pilosa coincided with bursts of tumor suppressor gene duplications; (3) cells from sloths proliferate extremely slowly while Xenarthran cells induce apoptosis at very low doses of DNA damaging agents; and (4) the prevalence of cancer is extremely low Xenarthrans, and cancer is nearly absent from armadillos. These data implicate the duplication of tumor suppressor genes in the evolution of remarkably large body sizes and decreased cancer risk in Xenarthrans and suggest they are a remarkably cancer-resistant group of mammals.

A pachyderm perfume: odour encodes identity and group membership in African elephants.

Group-living animals that live in complex social systems require effective modes of communication to maintain social cohesion, and several acoustic, olfactory and visual signaling systems have been described. Individuals need to discriminate between in- and out-group odour to both avoid inbreeding and to identify recipients for reciprocal behaviour. The presence of a unique group odour, identified in several social mammals, is a proposed mechanism whereby conspecifics can distinguish group from non-group members. African elephants (Loxodonta africana) live in stable, socially complex, multi-female, fission-fusion groups, characterized by female philopatry, male dispersal and linear dominance hierarchies. Elephant social behaviour suggests that individuals use odour to monitor the sex, reproductive status, location, health, identity and social status of conspecifics. To date, it is not clear what fixed or variable information is contained in African elephant secretions, and whether odour encodes kinship or group membership information. Here we use SPME GC-MS generated semiochemical profiles for temporal, buccal and genital secretions for 113 wild African elephants and test their relationship with measures of genetic relatedness. Our results reveal the existence of individual identity odour profiles in African elephants as well as a signature for age encoded in temporal gland and buccal secretions. Olfactory signatures for genetic relatedness were found in labial secretions of adult sisters. While group odour was not correlated with group genetic relatedness, our analysis identified "group membership" as a significant factor explaining chemical differences between social groups. Saturated and short-chain fatty acids (SCFAs), derived from key volatile compounds from bacterial fermentation, were identified in temporal, buccal and genital secretions suggesting that group odour in African elephants may be the result of bacterial elements of the gut microbiome. The frequent affiliative behavior of African elephants is posited as a likely mechanism for bacterial transmission. Our findings favour flexible group-specific bacterial odours, which have already been proposed for other social mammals and present a useful form of olfactory communication that promotes bond group cohesion among non-relatives in fission-fusion mammals.