Metabolic rate limits the effect of sperm competition on mammalian spermatogenesis.
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ABSTRACT:
SUBMITTER: delBarco-Trillo J
PROVIDER: S-EPMC3777943 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Two complementary hypotheses have been proposed to explain variation in sperm size. The first proposes that post-copulatory sexual selection favors an increase in sperm size because it enhances sperm swimming speed, which is an important determinant of fertilization success in competitive contexts. The second hypothesis proposes that mass-specific metabolic rate acts as a constraint, because large animals with low mass-specific metabolic rates will not be able to process resources at the rates needed to produce large sperm. This constraint is expected to be particularly pronounced among mammals, given that this group contains some of the largest species on Earth. We tested these hypotheses among marsupials, a group in which mass-specific metabolic rates are roughly 30% lower than those of eutherian mammals of similar size, leading to the expectation that metabolic rate should be a major constraint. Our findings support both hypotheses because levels of sperm competition are associated with increases in sperm size, but low mass-specific metabolic rate constrains sperm size among large species. We also found that the relationship between sperm size and mass-specific metabolic rate is steeper among marsupials and shallower among eutherian mammals. This finding has two implications: marsupials respond to changes in mass-specific metabolic rate by modifying sperm length to a greater extent, suggesting that they are more constrained by metabolic rate. In addition, for any given mass-specific metabolic rate, marsupials produce longer sperm. We suggest that this is the consequence of marsupials diverting resources away from sperm numbers and into sperm size, due to their efficient sperm transport along the female tract and the existence of mechanisms to protect sperm.
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Project description:BACKGROUND:An important component of sexual selection arises because females obtain viability benefits for their offspring from their mate choice. Females choosing extra-pair fertilization generally favor males with exaggerated secondary sexual characters, and extra-pair paternity increases the variance in male reproductive success. Furthermore, females are assumed to benefit from 'good genes' from extra-pair sires. How additive genetic variance in such viability genes is maintained despite strong directional selection remains an evolutionary enigma. We propose that sexual selection is associated with elevated mutation rates, changing the balance between mutation and selection, thereby increasing variance in fitness and hence the benefits to be obtained from good genes sexual selection. Two hypotheses may account for such elevated mutation: (1) Increased sperm production associated with sperm competition may increase mutation rate. (2) Mutator alleles increase mutation rates that are revealed by the expression of condition-dependent secondary sexual characters used by choosy females during their mate choice. M Petrie has independently developed the idea that mutator alleles may account for the maintenance of genetic variation in viability despite strong directional selection. RESULTS:A comparative study of birds revealed a positive correlation between mutation rate at minisatellite loci and extra-pair paternity, but not between mutation rate and relative testes mass which is a measure of relative sperm production. Minisatellite mutation rates were not related to longevity, suggesting a meiotic rather than a mitotic origin of mutations. CONCLUSION:We found evidence of increased mutation rate in species with more intense sexual selection. Increased mutation was not associated with increased sperm production, and we suggest that species with intense sexual selection may maintain elevated mutation rates because sexual selection continuously benefits viability alleles expressed in condition-dependent characters. Sexual selection may increase mutational input, which in turn feeds back on sexual selection because of increased variance in viability traits.
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Project description:Despite rapid evolution across eutherian mammals, the X-linked miR-506 family miRNAs are located in a region flanked by two highly conserved protein-coding genes (Slitrk2 and Fmr1) on the X chromosome. Intriguingly, these miRNAs are predominantly expressed in the testis, suggesting a potential role in spermatogenesis and male fertility. Here, we report that the X-linked miR-506 family miRNAs were derived from the MER91C DNA transposons. Selective inactivation of individual miRNAs or clusters caused no discernable defects, but simultaneous ablation of five clusters containing nineteen members of the miR-506 family led to reduced male fertility in mice. Despite normal sperm counts, motility and morphology, the KO sperm were less competitive than wild-type sperm when subjected to a polyandrous mating scheme. Transcriptomic and bioinformatic analyses revealed that these X-linked miR-506 family miRNAs, in addition to targeting a set of conserved genes, have more targets that are critical for spermatogenesis and embryonic development during evolution. Our data suggest that the miR-506 family miRNAs function to enhance sperm competitiveness and reproductive fitness of the male by finetuning gene expression during spermatogenesis.
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Project description:During mammalian spermatogenesis, the diploid spermatogonia mature into haploid spermatozoa through a highly controlled process of mitosis, meiosis and post-meiotic morphological remodeling (spermiogenesis). Despite important progress made in this area, the molecular mechanisms underpinning this transformation are poorly understood. Our analysis of the expression and function of the putative serine-threonine kinase Fused (Fu) provides critical insight into key steps in spermatogenesis. In this report, we demonstrate that conditional inactivation of Fu in male germ cells results in infertility due to diminished sperm count, abnormal head shaping, decapitation and motility defects of the sperm. Interestingly, mutant flagellar axonemes are intact but exhibit altered periaxonemal structures that affect motility. These data suggest that Fu plays a central role in shaping the sperm head and controlling the organization of the periaxonemal structures in the flagellum. We show that Fu localizes to multiple tubulin-containing or microtubule-organizing structures, including the manchette and the acrosome-acroplaxome complex that are involved in spermatid head shaping. In addition, Fu interacts with the outer dense fiber protein Odf1, a major component of the periaxonemal structures in the sperm flagellum, and Kif27, which is detected in the manchette. We propose that disrupted Fu function in these structures underlies the head and flagellar defects in Fu-deficient sperm. Since a majority of human male infertility syndromes stem from reduced sperm motility and structural defects, uncovering Fu?s role in spermiogenesis provides new insight into the causes of sterility and the biology of reproduction.
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Project description:Sperm cryopreservation for men with severely impaired spermatogenesis is one of the commonest reasons for short-term sperm storage, usually in advance of fertility treatment. Cryopreservation is generally very effective, although not all spermatozoa survive the process of freezing and thawing. This review considers various aspects of freezing sperm, including an overview of methods, appropriate use of cryoprotectants and practical considerations, as well as oxidative stress and mechanisms of cell cryodamage.
| S-EPMC9874962 | biostudies-literature
Project description:Sperm competition favors increases in relative testes mass and production efficiency, and changes in sperm phenotype that result in faster swimming speeds. However, little is known about its effects on traits that contribute to determine the quality of a whole ejaculate (i.e., proportion of motile, viable, morphologically normal and acrosome intact sperm) and that are key determinants of fertilization success. Two competing hypotheses lead to alternative predictions: (a) sperm quantity and quality traits co-evolve under sperm competition because they play complementary roles in determining ejaculate's competitive ability, or (b) energetic constraints force trade-offs between traits depending on their relevance in providing a competitive advantage. We examined relationships between sperm competition levels, sperm quantity, and traits that determine ejaculate quality, in a comparative study of 18 rodent species using phylogenetically controlled analyses. Total sperm numbers were positively correlated to proportions of normal sperm, acrosome integrity and motile sperm; the latter three were also significantly related among themselves, suggesting no trade-offs between traits. In addition, testes mass corrected for body mass (i.e., relative testes mass), showed a strong association with sperm numbers, and positive significant associations with all sperm traits that determine ejaculate quality with the exception of live sperm. An "overall sperm quality" parameter obtained by principal component analysis (which explained 85% of the variance) was more strongly associated with relative testes mass than any individual quality trait. Overall sperm quality was as strongly associated with relative testes mass as sperm numbers. Thus, sperm quality traits improve under sperm competition in an integrated manner suggesting that a combination of all traits is what makes ejaculates more competitive. In evolutionary terms this implies that a complex network of genetic and developmental pathways underlying processes of sperm formation, maturation, transport in the female reproductive tract, and preparation for fertilization must all evolve in concert.
| S-EPMC3064651 | biostudies-literature
Project description:Metabolism is linked with the pace-of-life, co-varying with survival, growth, and reproduction. Metabolic rates should therefore be under strong selection and, if heritable, become less variable over time. Yet intraspecific variation in metabolic rates is ubiquitous, even after accounting for body mass and temperature. Theory predicts variable selection maintains trait variation, but field estimates of how selection on metabolism varies are rare. We use a model marine invertebrate to estimate selection on metabolic rates in the wild under different competitive environments. Fitness landscapes varied among environments separated by a few centimeters: interspecific competition selected for higher metabolism, and a faster pace-of-life, relative to competition-free environments. Populations experience a mosaic of competitive regimes; we find metabolism mediates a competition-colonization trade-off across these regimes. Although high metabolic phenotypes possess greater competitive ability, in the absence of competitors, low metabolic phenotypes are better colonizers. Spatial heterogeneity and the variable selection on metabolic rates that it generates is likely to maintain variation in metabolic rate, despite strong selection in any single environment.
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Project description:Adult germline stem cells (AGSCs) are multifunctional - they must self renew, maintain genome pluripotency, and prepare for gametogenesis – which involves meiotic and chromatin repackaging phases. To better understand AGSCs and gametogenesis, we derived high-resolution profiles of transcription, DNA methylation, 5hmC, and multiple histone modifications at key stages. First, AGSCs display chromatin ‘poising’ of enhancers and promoters of genes utilized in embryo development. Second, the pluripotency network in AGSCs is remarkably distinct from ESCs - lacking Nanog, Sox2, or Prdm14 expression. Third, spermatogenesis involves stage-specific transcription and distinctive chromatin dynamics, but virtually no changes in DNAme. Surprisingly, we observe co-incidence of RNA polymerase II, high H3K4me3, and DNA methylation at 20-35% of genes transcribed during gametogenesis - including piRNA clusters - but often observe attendant promoter 5hmC. Our work reveals key differences between AGSCs and other germ/stem cells, and reveals both logical and unexpected chromatin-transcription relationships accompanying germline developmental transitions. mRNA and small RNA profiles of human sperm generated by deep sequencing using Illumina HiSeq 2000 and Illumina Genome Analyzer II.
2014-05-19 | E-GEOD-57096 | biostudies-arrayexpress
Project description:Adult germline stem cells (AGSCs) are multifunctional - they must self renew, maintain genome pluripotency, and prepare for gametogenesis – which involves meiotic and chromatin repackaging phases. To better understand AGSCs and gametogenesis, we derived high-resolution profiles of transcription, DNA methylation, 5hmC, and multiple histone modifications at key stages. First, AGSCs display chromatin ‘poising’ of enhancers and promoters of genes utilized in embryo development. Second, the pluripotency network in AGSCs is remarkably distinct from ESCs - lacking Nanog, Sox2, or Prdm14 expression. Third, spermatogenesis involves stage-specific transcription and distinctive chromatin dynamics, but virtually no changes in DNAme. Surprisingly, we observe co-incidence of RNA polymerase II, high H3K4me3, and DNA methylation at 20-35% of genes transcribed during gametogenesis - including piRNA clusters - but often observe attendant promoter 5hmC. Our work reveals key differences between AGSCs and other germ/stem cells, and reveals both logical and unexpected chromatin-transcription relationships accompanying germline developmental transitions. Methylation profiles of human sperm were generated by bisulfite sequencing using Illumina HiSeq 2000.
2014-05-19 | E-GEOD-57097 | biostudies-arrayexpress
Project description:Adult germline stem cells (AGSCs) are multifunctional - they must self renew, maintain genome pluripotency, and prepare for gametogenesis – which involves meiotic and chromatin repackaging phases. To better understand AGSCs and gametogenesis, we derived high-resolution profiles of transcription, DNA methylation, 5hmC, and multiple histone modifications at key stages. First, AGSCs display chromatin ‘poising’ of enhancers and promoters of genes utilized in embryo development. Second, the pluripotency network in AGSCs is remarkably distinct from ESCs - lacking Nanog, Sox2, or Prdm14 expression. Third, spermatogenesis involves stage-specific transcription and distinctive chromatin dynamics, but virtually no changes in DNAme. Surprisingly, we observe co-incidence of RNA polymerase II, high H3K4me3, and DNA methylation at 20-35% of genes transcribed during gametogenesis - including piRNA clusters - but often observe attendant promoter 5hmC. Our work reveals key differences between AGSCs and other germ/stem cells, and reveals both logical and unexpected chromatin-transcription relationships accompanying germline developmental transitions. Examination of 3 different histone modifications in human sperm
2014-05-19 | E-GEOD-57095 | biostudies-arrayexpress