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Population-specific, recent positive directional selection suggests adaptation of human male reproductive genes to different environmental conditions.

ABSTRACT: BACKGROUND:Recent human transcriptomic analyses revealed a very large number of testis-enriched genes, many of which are involved in spermatogenesis. This comprehensive transcriptomic data lead us to the question whether positive selection was a decisive force influencing the evolution and variability of testis-enriched genes in humans. We used two methodological approaches to detect different levels of positive selection, namely episodic positive diversifying selection (i.e., past selection) in the human lineage within primate phylogeny, potentially driven by sperm competition, and recent positive directional selection in contemporary human populations, which would indicate adaptation to different environments. RESULTS:In the human lineage (after correction for multiple testing) we found that only the gene TULP2, for which no functional data are yet available, is subject to episodic positive diversifying selection. Using less stringent statistical criteria (uncorrected p-values), also the gene SPATA16, which has a pivotal role in male fertility and for which episodes of adaptive evolution have been suggested, also displays a putative signal of diversifying selection in the human branch. At the same time, we found evidence for recent positive directional selection acting on several human testis-enriched genes (MORC1, SLC9B1, ROPN1L, DMRT1, PLCZ1, RNF17, FAM71D and WBP2NL) that play important roles in human spermatogenesis and fertilization. Most of these genes are population-specifically under positive selection. CONCLUSION:Episodic diversifying selection, possibly driven by sperm competition, was not an important force driving the evolution of testis-enriched genes in the human lineage. Population-specific, recent positive directional selection suggests an adaptation of male reproductive genes to different environmental conditions. Positive selection acts on eQTLS and sQTLs, indicating selective effects on important gene regulatory functions. In particular, the transcriptional diversity regulated by sQTLs in testis-enriched genes may be important for spermatocytes to respond to environmental and physiological stress.

SUBMITTER: Schaschl H

PROVIDER: S-EPMC7020506 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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Population-specific, recent positive directional selection suggests adaptation of human male reproductive genes to different environmental conditions.

Schaschl Helmut H Wallner Bernard B

BMC evolutionary biology 20200213 1

<h4>Background</h4>Recent human transcriptomic analyses revealed a very large number of testis-enriched genes, many of which are involved in spermatogenesis. This comprehensive transcriptomic data lead us to the question whether positive selection was a decisive force influencing the evolution and variability of testis-enriched genes in humans. We used two methodological approaches to detect different levels of positive selection, namely episodic positive diversifying selection (i.e., past selec ...[more]

PMID: 32054438

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Project description:Environmental toxicants, such as cadmium and bisphenol A (BPA) are endocrine disruptors. In utero, perinatal or neonatal exposure of BPA to rats affect the male reproductive function, such as the blood-testis barrier (BTB) integrity. This effect of BPA on BTB integrity in immature rats is likely mediated via a loss of gap junction function at the BTB, failing to coordinate tight junction and anchoring junction function at the site to maintain the immunological barrier integrity. This in turn activates the extracellular signal-regulated kinases 1/2 (Erk1/2) downstream and an increase in protein endocytosis, destabilizing the BTB. The cadmium-induced disruption of testicular dysfunction is mediated initially via its effects on the occludin/ZO-1/focal adhesion kinase (FAK) complex at the BTB, causing redistribution of proteins at the Sertoli-Sertoli cell interface, leading to the BTB disruption. The damaging effects of these toxicants to testicular function are mediated by mitogen-activated protein kinases (MAPK) downstream, which in turn perturbs the actin bundling and accelerates the actin-branching activity, causing disruption of the Sertoli cell tight junction (TJ)-barrier function at the BTB and perturbing spermatid adhesion at the apical ectoplasmic specialization (apical ES, a testis-specific anchoring junction type) that leads to premature release of germ cells from the testis. However, the use of specific inhibitors against MAPK was shown to block or delay the cadmium-induced testicular injury, such as BTB disruption and germ cell loss. These findings suggest that there may be a common downstream p38 and/or Erk1/2 MAPK-based signaling pathway involving polarity proteins and actin regulators that is shared between different toxicants that induce male reproductive dysfunction. As such, the use of inhibitors and/or antagonists against specific MAPKs can possibly be used to "manage" the illnesses caused by these toxicants and/or "protect" industrial workers being exposed to high levels of these toxicants in their work environment.

Project description:Male reproductive disorders that are of interest from an environmental point of view include sexual dysfunction, infertility, cryptorchidism, hypospadias and testicular cancer. Several reports suggest declining sperm counts and increase of these reproductive disorders in some areas during some time periods past 50 years. Except for testicular cancer this evidence is circumstantial and needs cautious interpretation. However, the male germ line is one of the most sensitive tissues to the damaging effects of ionizing radiation, radiant heat and a number of known toxicants. So far occupational hazards are the best documented risk factors for impaired male reproductive function and include physical exposures (radiant heat, ionizing radiation, high frequency electromagnetic radiation), chemical exposures (some solvents as carbon disulfide and ethylene glycol ethers, some pesticides as dibromochloropropane, ethylendibromide and DDT/DDE, some heavy metals as inorganic lead and mercury) and work processes such as metal welding. Improved working conditions in affluent countries have dramatically decreased known hazardous workplace exposures, but millions of workers in less affluent countries are at risk from reproductive toxicants. New data show that environmental low-level exposure to biopersistent pollutants in the diet may pose a risk to people in all parts of the world. For other toxicants the evidence is only suggestive and further evaluation is needed before conclusions can be drawn. Whether compounds as phthalates, bisphenol A and boron that are present in a large number of industrial and consumer products entails a risk remains to be established. The same applies to psychosocial stressors and use of mobile phones. Finally, there are data indicating a particular vulnerability of the fetal testis to toxicants-for instance maternal tobacco smoking. Time has come where male reproductive toxicity should be addressed form entirely new angles including exposures very early in life.

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Population-specific, recent positive directional selection suggests adaptation of human male reproductive genes to different environmental conditions.

Publications

Population-specific, recent positive directional selection suggests adaptation of human male reproductive genes to different environmental conditions.

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