The androgen receptor and prostate cancer: A role for sexual selection and sexual conflict?

Reproductive endocrinology and aging in human males: An evolutionary perspective

Due to its important role in fertility, reproductive endocrine function has been subject to natural selection in all organisms including human males. Moreover, reproductive endocrine function is subject to change as males age. Indeed, the biology of aging is also subject to natural selection. As males age, hormone function such as variation in testosterone can change as the result of general somatic degradation. However these changes are not universal and can differ between human male populations depending on lifestyle and ecological context. The degree to which this variation is adaptive remains an open question but recent evolutionary anthropology research has provided some clarity. While knowledge of evolutionary approaches has limitations, the benefits of understanding the origins and comparative context of reproductive endocrine function in older human males are significant. This paper discusses our present comprehension of reproductive endocrinology and aging in human males, with a focus on human diversity across varied lifestyles, ecologies, and environments. In addition, comparative great ape research is examined. Current research challenges and future directions related to the importance of evolutionary biology and human diversity for understanding human male aging are discussed.

Cancer Susceptibility as a Cost of Reproduction and Contributor to Life History Evolution

Reproduction is one of the most energetically demanding life-history stages. As a result, breeding individuals often experience trade-offs, where energy is diverted away from maintenance (cell repair, immune function) toward reproduction. While it is increasingly acknowledged that oncogenic processes are omnipresent, evolving and opportunistic entities in the bodies of metazoans, the associations among reproductive activities, energy expenditure, and the dynamics of malignant cells have rarely been studied. Here, we review the diverse ways in which age-specific reproductive performance (e.g., reproductive aging patterns) and cancer risks throughout the life course may be linked via trade-offs or other mechanisms, as well as discuss situations where trade-offs may not exist. We argue that the interactions between host–oncogenic processes should play a significant role in life-history theory, and suggest some avenues for future research.

Advancing genomic technologies and clinical awareness accelerates discovery of disease-associated tandem repeat sequences

Expansions of gene-specific DNA tandem repeats (TRs), first described in 1991 as a disease-causing mutation in humans, are now known to cause >60 phenotypes, not just disease, and not only in humans. TRs are a common form of genetic variation with biological consequences, observed, so far, in humans, dogs, plants, oysters, and yeast. Repeat diseases show atypical clinical features, genetic anticipation, and multiple and partially penetrant phenotypes among family members. Discovery of disease-causing repeat expansion loci accelerated through technological advances in DNA sequencing and computational analyses. Between 2019 and 2021, 17 new disease-causing TR expansions were reported, totaling 63 TR loci (>69 diseases), with a likelihood of more discoveries, and in more organisms. Recent and historical lessons reveal that properly assessed clinical presentations, coupled with genetic and biological awareness, can guide discovery of disease-causing unstable TRs. We highlight critical but underrecognized aspects of TR mutations. Repeat motifs may not be present in current reference genomes but will be in forthcoming gapless long-read references. Repeat motif size can be a single nucleotide to kilobases/unit. At a given locus, repeat motif sequence purity can vary with consequence. Pathogenic repeats can be "insertions" within nonpathogenic TRs. Expansions, contractions, and somatic length variations of TRs can have clinical/biological consequences. TR instabilities occur in humans and other organisms. TRs can be epigenetically modified and/or chromosomal fragile sites. We discuss the expanding field of disease-associated TR instabilities, highlighting prospects, clinical and genetic clues, tools, and challenges for further discoveries of disease-causing TR instabilities and understanding their biological and pathological impacts-a vista that is about to expand.

Socio-reproductive Conflicts and the Father's Curse Dilemma

Evolutionary conflicts between males and females can manifest over sexually antagonistic interactions at loci or over sexually antagonistic interests within a locus. The latter form of conflict, intralocus sexual conflict, arises from sexually antagonistic selection and constrains the fitness of individuals through a phenotypic compromise. These conflicts, and socio-reproductive interactions in general, are commonly mediated by hormones, and thus predictive insights can be gained from studying their mediating effects. Here, we integrate several lines of evidence to describe a novel, hormonally mediated reproductive dilemma that we call the father's curse, which results from an intralocus conflict between mating and parental efforts. Essentially, a genetic locus exerts pleiotropic and antagonistic effects on the mating effort of one individual and the parental effort of a related individual who is the primary provider of parental care. We outline the criteria for operation of the father's curse dilemma, provide evidence of the phenomenon, and discuss the predictions and outcomes arising from its dynamics. By integrating the effects of hormones into socio-reproductive conflicts and socio-reproductive effort, clearer links between genotypes, phenotypes, and fitness can be established.

Cancer: A disease at the crossroads of trade-offs

Central to evolutionary theory is the idea that living organisms face phenotypic and/or genetic trade-offs when allocating resources to competing life-history demands, such as growth, survival, and reproduction. These trade-offs are increasingly considered to be crucial to further our understanding of cancer. First, evidences suggest that neoplastic cells, as any living entities subject to natural selection, are governed by trade-offs such as between survival and proliferation. Second, selection might also have shaped trade-offs at the organismal level, especially regarding protective mechanisms against cancer. Cancer can also emerge as a consequence of additional trade-offs in organisms (e.g., eco-immunological trade-offs). Here, we review the wide range of trade-offs that occur at different scales and their relevance for understanding cancer dynamics. We also discuss how acknowledging these phenomena, in light of human evolutionary history, may suggest new guidelines for preventive and therapeutic strategies.

Cancer susceptibility and reproductive trade-offs: a model of the evolution of cancer defences

The factors influencing cancer susceptibility and why it varies across species are major open questions in the field of cancer biology. One underexplored source of variation in cancer susceptibility may arise from trade-offs between reproductive competitiveness (e.g. sexually selected traits, earlier reproduction and higher fertility) and cancer defence. We build a model that contrasts the probabilistic onset of cancer with other, extrinsic causes of mortality and use it to predict that intense reproductive competition will lower cancer defences and increase cancer incidence. We explore the trade-off between cancer defences and intraspecific competition across different extrinsic mortality conditions and different levels of trade-off intensity, and find the largest effect of competition on cancer in species where low extrinsic mortality combines with strong trade-offs. In such species, selection to delay cancer and selection to outcompete conspecifics are both strong, and the latter conflicts with the former. We discuss evidence for the assumed trade-off between reproductive competitiveness and cancer susceptibility. Sexually selected traits such as ornaments or large body size require high levels of cell proliferation and appear to be associated with greater cancer susceptibility. Similar associations exist for female traits such as continuous egg-laying in domestic hens and earlier reproductive maturity. Trade-offs between reproduction and cancer defences may be instantiated by a variety of mechanisms, including higher levels of growth factors and hormones, less efficient cell-cycle control and less DNA repair, or simply a larger number of cell divisions (relevant when reproductive success requires large body size or rapid reproductive cycles). These mechanisms can affect intra- and interspecific variation in cancer susceptibility arising from rapid cell proliferation during reproductive maturation, intrasexual competition and reproduction.

A test of somatic mosaicism in the androgen receptor gene of Canada lynx (Lynx canadensis)

Background

The androgen receptor, an X-linked gene, has been widely studied in human populations because it contains highly polymorphic trinucleotide repeat motifs that have been associated with a number of adverse human health and behavioral effects. A previous study on the androgen receptor gene in carnivores reported somatic mosaicism in the tissues of a number of species including Eurasian lynx (Lynx lynx). We investigated this claim in a closely related species, Canada lynx (Lynx canadensis). The presence of somatic mosaicism in lynx tissues could have implications for the future study of exonic trinucleotide repeats in landscape genomic studies, in which the accurate reporting of genotypes would be highly problematic.

Methods

To determine whether mosaicism occurs in Canada lynx, two lynx individuals were sampled for a variety of tissue types (lynx 1) and tissue locations (lynx 1 and 2), and 1,672 individuals of known sex were genotyped to further rule out mosaicism.

Results

We found no evidence of mosaicism in tissues from the two necropsied individuals, or any of our genotyped samples.

Conclusions

Our results indicate that mosaicism does not manifest in Canada lynx. Therefore, the use of hide samples for further work involving trinucleotide repeat polymorphisms in Canada lynx is warranted.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-015-0284-y) contains supplementary material, which is available to authorized users.

Applying ecological and evolutionary theory to cancer: a long and winding road

Since the mid 1970s, cancer has been described as a process of Darwinian evolution, with somatic cellular selection and evolution being the fundamental processes leading to malignancy and its many manifestations (neoangiogenesis, evasion of the immune system, metastasis, and resistance to therapies). Historically, little attention has been placed on applications of evolutionary biology to understanding and controlling neoplastic progression and to prevent therapeutic failures. This is now beginning to change, and there is a growing international interest in the interface between cancer and evolutionary biology. The objective of this introduction is first to describe the basic ideas and concepts linking evolutionary biology to cancer. We then present four major fronts where the evolutionary perspective is most developed, namely laboratory and clinical models, mathematical models, databases, and techniques and assays. Finally, we discuss several of the most promising challenges and future prospects in this interdisciplinary research direction in the war against cancer.

Androgen receptor polyglutamine repeat number: models of selection and disease susceptibility

Variation in polyglutamine repeat number in the androgen receptor (AR CAGn) is negatively correlated with the transcription of androgen-responsive genes and is associated with susceptibility to an extensive list of human disease. Only a small portion of the heritability for many of these diseases is explained by conventional SNP-based genome-wide association studies, and the forces shaping AR CAGn among humans remains largely unexplored. Here, we propose evolutionary models for understanding selection at the AR CAG locus, namely balancing selection, sexual conflict, accumulation-selection, and antagonistic pleiotropy. We evaluate these models by examining AR CAGn-linked susceptibility to eight extensively studied diseases representing the diverse physiological roles of androgens, and consider the costs of these diseases by their frequency and fitness effects. Five diseases could contribute to the distribution of AR CAGn observed among contemporary human populations. With support for disease susceptibilities associated with long and short AR CAGn, balancing selection provides a useful model for studying selection at this locus. Gender-specific differences AR CAGn health effects also support this locus as a candidate for sexual conflict over repeat number. Accompanied by the accumulation of AR CAGn in humans, these models help explain the distribution of repeat number in contemporary human populations.

Antagonistic pleiotropy as a widespread mechanism for the maintenance of polymorphic disease alleles

BACKGROUND

Many serious diseases have a genetic basis which, from an evolutionary point of view, should have been selected against, resulting in very low frequencies. The remarkable sustained prevalence of a number of disease-associated alleles is therefore surprising. We believe that antagonistic pleiotropy, when multiple effects of a gene have opposing effects on fitness (e.g., sickle cell disease), may be more widespread than typically considered. We hypothesize that, rather than being an exception to the rule of genetic disorders, antagonistic pleiotropy may be common.

METHODS

We surveyed the medical literature in order to determine whether sufficient evidence exists to reassess the nature of antagonistic pleiotropy; from being considered an unusual scenario to one that is anticipated. We also used a simple population genetic model to examine the feasibility of antagonistic pleiotropy to act as a mechanism to maintain polymorphism for serious genetic disorders even if the benefits are subtle.

RESULTS

We identified a number of examples of antagonistic pleiotropy where the deleterious effect, the beneficial effect, and the exact molecular cause have been demonstrated. We also identified putative cases in which there is circumstantial evidence or a strong reason to expect antagonistic pleiotropy in a genetic disorder. The population genetic model demonstrates that alleles with severe deleterious health effects can be maintained at medically relevant frequencies with only minor beneficial pleiotropic effects.

CONCLUSION

We believe that our identification of several cases of antagonistic pleiotropy, despite the lack of research on this question and the varied natures of the types of these disorders, speaks to both the underappreciated nature of this phenomenon and its potentially fundamental importance. If antagonistic pleiotropy is as common as our research suggests, this may explain why so many serious diseases, even apparently environmentally caused ones, have a genetic component. Furthermore, acceptance of a genome full of antagonistically pleiotropic genetic interactions poses important implications for clinical treatment and disease prevention research, especially genetically based therapies.

Acne, dairy and cancer: The 5alpha-P link

A potent link to dairy seems to exist for three hormone-responsive glands. Acne, breast cancer and prostate cancer have all been linked epidemiologically to dairy intake. Although mechanisms postulated here remain to be accurately defined, the likely link involves Insulin-like Growth Factor-1 as a general stimulant, synergized by the steroid hormones present in milk. The IGF-1 may be either absorbed from milk, or stimulated by its ingestion, or both. The 5alpha-reduced compound 5alpha-pregnanedione (5alpha-P) present in milk is a direct precursor of dihydrotestosterone and may act through that pathway in prostate cancer, but 5alpha-P has also recently been shown to be capable of inducing estrogen receptors in breast cancer cells, upregulating cancer cells' sensitivity to estrogen. The introduction of exogenous hormones and growth factors into tissues that have not evolved defensive feedback inhibition of their corresponding endogenous sources is postulated as a direct stimulatory threat to these organ systems, whether for hyperplasia or neoplasia.

Polymorphism of CAG repeats in androgen receptor of carnivores

Androgen effect is mediated by the androgen receptor (AR). The polymorphism of CAG triplet repeat (polyCAG), in the N-terminal transactivation domain of the AR protein, has been involved either in endocrine or neurological disorders in human. We obtained partial sequence of AR exon 1 in 10 carnivore species. In most carnivore species, polyglutamine length polymorphism presented in all three CAG repeat regions of AR, in contrast, only CAG-I site polymorphism presented in primate species, and CAG-I and CAG-III sites polymorphism presented in Canidae. Therefore, studies focusing on disease-associated polymorphism of poly(CAG) in carnivore species AR should investigate all three CAG repeats sites, and should not only consider CAG-I sites as the human disease studies. The trinucleotide repeat length in carnivore AR exon 1 had undergone from expansions to contractions during carnivores evolution, unlike a linear increase in primate species. Furthermore, the polymorphisms of the triplet-repeats in the same tissue (somatic mosaicism) were demonstrated in Moutain weasel, Eurasian lynx, Clouded leopard, Chinese tiger, Black leopard and Leopard AR. And, the abnormal stop codon was found in the exon 1 of three carnivore species AR (Moutain weasel, Eurasian lynx and Black leopard). It seemed to have a high frequency presence of tissue-specific somatic in carnivores AR genes. Thus the in vivo mechanism leading to such highly variable phenotypes of the described mutations, and their impact on these animals, are worthwhile to be further elucidated.

How pleiotropic genetics of the musculoskeletal system can inform genomics and phenomics of aging

Genetic study can provide insight into the biologic mechanisms underlying inter-individual differences in susceptibility to (or resistance to) organisms' aging. Recent advances in molecular genetics and genetic epidemiology provide the necessary tools to perform a study of the genetic sources of biological aging. However, to be successful, the genetic study of a complex condition requires a heritable phenotype to be developed and validated. Genome-wide association studies offer an unbiased approach to identify new candidate genes for human diseases. It is hypothesized that convergent results from multiple aging-related traits will point out the genes responsible for the general aging of the organism. This perspective focuses on the musculoskeletal aging as an example of an approach to identify a downstream common pathway that summarizes aging processes. Since the musculoskeletal traits are linked to the state of many vital functions, disability, and ultimately survival rates, we postulate that there is significance in studying musculoskeletal aging. Construction of an integrated phenotype of aging can be achieved based on shared genetics among multiple musculoskeletal biomarkers. Valid biomarkers from other systems of the organism should be similarly explored. The new composite aging score needs to be validated by determining whether it predicts all-cause mortality, incidences of major chronic diseases, and disability late in life. Comprehensive databases on biomarkers of musculoskeletal aging in multiple large cohort studies, along with information on various health outcomes, are needed to validate the proposed measure of biological aging.

Xmrks the spot: life history tradeoffs, sexual selection and the evolutionary ecology of oncogenesis

In a classic paper, George Williams (1957) argued that alleles promoting reproductive success early in life may be favoured by selection, even if they reduce the lifespan of individuals that bear the allele. A variety of evidence supports the theory that such 'antagonistic pleiotropy' is a major factor contributing to the evolution of senescence (Ljubuncic & Reznick 2009), but examples of specific alleles known to fulfil Williams' criteria remain rare, in both humans and other animals (e.g. Alexander et al. 2007; Kulminski et al. 2010). An intriguing example in this issue of Molecular Ecology (Fernandez & Bowser 2010) demonstrates that both natural and sexual selection may favour melanoma-promoting oncogene alleles in the fish genus Xiphophorus.

Selection for a dominant oncogene and large male size as a risk factor for melanoma in the Xiphophorus animal model

Adult height is a risk factor in numerous human cancers that involve aberrant receptor tyrosine kinase (RTK) signalling. However, its importance is debated due to conflicting epidemiological studies and the lack of useful in vivo models. In Xiphophorus fishes (Platyfishes/Swordtails), a functional RTK, Xiphophorus melanoma receptor kinase (Xmrk), serves as the dominant oncogene and has been maintained for several million years despite being deleterious and in an extremely unstable genomic region. Here we show that the Xmrk genotype is positively correlated with standard length in male and female wild caught Xiphophorus cortezi sampled throughout their phylogeographic distribution. Histopathology confirms the occurrence of malignant melanomas in both sexes; however, melanoma incidence was extremely male biased. Furthermore, males collected with malignant melanomas in the field were significantly larger than both Xmrk males collected without melanomas and wildtype (Xmrk deficient) males. These results not only provide a novel selective mechanism for the persistence of the germline Xmrk oncogene but also create an innovative avenue of melanoma research within the Xiphophorus fishes. Wildlife cancer in natural systems is a growing concern, therefore, future research investigating life history characteristics associated with certain phenotypes and genotypes that predispose an individual to cancer will be fundamental to increasing our understanding of the evolutionary biology of cancer in nature as well as in humans.

Structural changes in exon 11 of MEF2A are not related to sporadic coronary artery disease in Han Chinese population

BACKGROUND

A mutation in MEF2A (myocyte enhancer factor-2A) had been reported to be the first gene linked directly to coronary artery disease (CAD). However, an opposing opinion was proposed recently that MEF2A mutations are not a common cause of sporadic CAD. In this study, we screened exon 11 of the MEF2A gene in people of the Han nationality in China and finished some functional analysis of found variations.

MATERIALS AND METHODS

A gene structural investigation of MEF2A in 257 CAD patients and 154 control individuals were developed in this study. Subsequently, typical MEF2A variations were cloned and expressed in HeLa or 293T cell line to illustrate whether found structure changes could influence the main biological functions of these proteins. At last, another set of gene structural screen was initialized to get more reliable conclusions.

RESULTS

Totally 16 different variations were detected in exon 11 of this gene in the first set of gene structural screen. By cloning and expressing typical MEF2A proteins in cultured cells, all the acquired MEF2A variations had transcriptional activation capabilities and subcellular localization patterns similar to those of the wild-type protein. Further larger scale genetic screening also revealed that the reported genetic variations of MEF2A did not differ significantly between CAD patients and healthy controls.

CONCLUSIONS

Our results reveal that structural changes of exon 11 in MEF2A are not involved in sporadic CAD in the Han population of China.

A cancer-causing gene is positively correlated with male aggression in Xiphophorus cortezi

The persistence of seemingly maladaptive genes in organisms challenges evolutionary biological thought. In Xiphophorus fishes, certain melanin patterns form malignant melanomas because of a cancer-causing gene (Xiphophorus melanoma receptor kinase; Xmrk), which arose several millions years ago from unequal meiotic recombination. Xiphophorus melanomas are male biased and induced by androgens however male behaviour and Xmrk genotype has not been investigated. This study found that male X. cortezi with the spotted caudal (Sc) pattern, from which melanomas originate, displayed increased aggression in mirror image trials. Furthermore, Xmrk males (regardless of Sc phenotype) bit and performed more agonistic displays than Xmrk deficient males. Male aggressive response decreased when males viewed their Sc image as compared with their non-Sc image. Collectively, these results indicate that Xmrk males experience a competitive advantage over wild-type males and that intrasexual selection could be an important component in the evolutionary maintenance of this oncogene within Xiphophorus.

Mate choice for more melanin as a mechanism to maintain a functional oncogene

The mechanisms by which cancer evolves and persists in natural systems have been difficult to ascertain. In the Xiphophorus melanoma model, a functional oncogene (Xiphophorus melanoma receptor kinase Xmrk) has been maintained for several million years despite being deleterious and in an extremely unstable genomic region. Melanomas in Xiphophorus spp. fishes (platyfishes and swordtails) have been investigated since the 1920s, and, yet, positive selection that could explain the maintenance of Xmrk has not been found. Here, we show that Xiphophorus cortezi females from two populations prefer males with the spotted caudal (Sc) melanin pattern, which is associated with the presence of the Xmrk oncogene and serves as the site of melanoma formation within this species. Moreover, X. cortezi females prefer males with an enhanced Sc to males with a reduced Sc pattern. RT-PCR analysis confirms tissue-specific Xmrk expression within the Sc pattern in X. cortezi. Because of the association of Xmrk with the Sc pigment pattern and the fact that melanoma formation augments this visual signal, sexual selection appears to be maintaining this oncogene because of a mating preference for Sc, as well as the exaggeration of this male trait. At the individual level, decreases in viability and fecundity because of Xmrk and subsequent melanoma formation may be mitigated via increases in mate acquisition. At the population level, maintenance of this oncogene appears to be under frequency dependent selection, as we detected female preference for males without Sc in a third population that had higher frequencies of Sc in females.