Flagellar ultrastructure suppresses buckling instabilities and enables mammalian sperm navigation in high-viscosity media

Eukaryotic flagellar swimming is driven by a slender motile unit, the axoneme, which possesses an internal structure that is essentially conserved in a tremendous diversity of sperm. Mammalian sperm, however, which are internal fertilizers, also exhibit distinctive accessory structures that further dress the axoneme and alter its mechanical response. This raises the following two fundamental questions. What is the functional significance of these structures? How do they affect the flagellar waveform and ultimately cell swimming? Hence we build on previous work to develop a mathematical mechanical model of a virtual human sperm to examine the impact of mammalian sperm accessory structures on flagellar dynamics and motility. Our findings demonstrate that the accessory structures reinforce the flagellum, preventing waveform compression and symmetry-breaking buckling instabilities when the viscosity of the surrounding medium is increased. This is in agreement with previous observations of internal and external fertilizers, such as human and sea urchin spermatozoa. In turn, possession of accessory structures entails that the progressive motion during a flagellar beat cycle can be enhanced as viscosity is increased within physiological bounds. Hence the flagella of internal fertilizers, complete with accessory structures, are predicted to be advantageous in viscous physiological media compared with watery media for the fundamental role of delivering a genetic payload to the egg.

Download Full-text

Grain Size in Mg Alloys: Recrystallization and Mechanical Consequences

Materials Science Forum ◽

10.4028/www.scientific.net/msf.558-559.433 ◽

2007 ◽

Vol 558-559 ◽

pp. 433-440 ◽

Cited By ~ 14

Author(s):

Matthew R. Barnett ◽

Dale Atwell ◽

Aiden G. Beer

Keyword(s):

Grain Size ◽

Dynamic Recrystallization ◽

Grain Refinement ◽

Magnesium Alloys ◽

Mechanical Response ◽

Deformation Twinning ◽

Simultaneous Increase ◽

The Impact ◽

Strength And Ductility

The present paper examines the development of grain size during the recrystallization of magnesium alloys and the influence the grain size has on the mechanical response. In magnesium alloys grain refinement improves the strength-ductility balance. This simultaneous increase in both strength and ductility is ascribed to the impact the grain size has on deformation twinning. The mechanisms by which the grain size is established during hot working are shown to be conventional dynamic recrystallization followed by post-dynamic recrystallization. The role of alloying addition on both of these reactions is briefly considered.

Download Full-text

Genetic Association in the Maintenance of the Mitochondrial Microenvironment and Sperm Capacity

Oxidative Medicine and Cellular Longevity ◽

10.1155/2021/5561395 ◽

2021 ◽

Vol 2021 ◽

pp. 1-12

Author(s):

Hwang I. S. Thomas ◽

Ying-Shiuan Chen ◽

Ching-Han Hung ◽

Dilip Bhargava Sreerangaraja Urs ◽

Tien-Ling Liao ◽

...

Keyword(s):

Reactive Oxygen Species ◽

Sperm Motility ◽

Manganese Superoxide Dismutase ◽

Uncoupling Protein ◽

Reactive Oxygen ◽

Human Sperm ◽

Oxygen Species ◽

Genotype Frequencies ◽

The Impact

Sperm motility is one of the major determinants of male fertility. Since sperm need a great deal of energy to support their fast movement by active metabolism, they are thus extremely vulnerable to oxidative damage by the reactive oxygen species (ROS) and other free radicals generated as byproducts in the electron transport chain. The present study is aimed at understanding the impact of a mitochondrial oxidizing/reducing microenvironment in the etiopathology of male infertility. We detected the mitochondrial DNA (mtDNA) 4,977 bp deletion in human sperm. We examined the gene mutation of ATP synthase 6 (ATPase6 m.T8993G) in ATP generation, the gene polymorphisms of uncoupling protein 2 (UCP2, G-866A) in the uncoupling of oxidative phosphorylation, the role of genes such as manganese superoxide dismutase (MnSOD, C47T) and catalase (CAT, C-262T) in the scavenging system in neutralizing reactive oxygen species, and the role of human 8-oxoguanine DNA glycosylase (hOGG1, C1245G) in 8-hydroxy-2 ′ -deoxyguanosine (8-OHdG) repair. We found that the sperm with higher motility were found to have a higher mitochondrial membrane potential and mitochondrial bioenergetics. The genotype frequencies of UCP2 G-866A, MnSOD C47T, and CAT C-262T were found to be significantly different among the fertile subjects, the infertile subjects with more than 50% motility, and the infertile subjects with less than 50% motility. A higher prevalence of the mtDNA 4,977 bp deletion was found in the subjects with impaired sperm motility and fertility. Furthermore, we found that there were significant differences between the occurrences of the mtDNA 4,977 bp deletion and MnSOD (C47T) and hOGG1 (C1245G). In conclusion, the maintenance of the mitochondrial redox microenvironment and genome integrity is an important issue in sperm motility and fertility.

Download Full-text

Age-associated sperm DNA methylation patterns do not directly persist trans-generationally

Epigenetics & Chromatin ◽

10.1186/s13072-019-0323-4 ◽

2019 ◽

Vol 12 (1) ◽

Cited By ~ 4

Author(s):

Timothy G. Jenkins ◽

Emma R. James ◽

Kenneth I. Aston ◽

Albert Salas-Huetos ◽

Alexander W. Pastuszak ◽

...

Keyword(s):

Dna Methylation ◽

Large Scale ◽

Human Sperm ◽

Paternal Age ◽

Sperm Dna ◽

Two Generations ◽

Methylation Patterns ◽

The Impact ◽

Sperm Dna Methylation

Abstract Background The impact of aging on the sperm methylome is well understood. However, the direct, subsequent impact on offspring and the role of altered sperm DNA methylation alterations in this process remain poorly understood. The well-defined impact of aging on sperm DNA methylation represents an excellent opportunity to trace the direct, transgenerational transmission of these signals. Results We utilized the Illumina MethylationEPIC array to analyze the sperm of 16 patients with older (> 40 years of age) paternal grandfathers (‘old grand paternal age’ patients; OGPA) and 16 patients with younger (< 25 years of age) grandfathers (‘young grand paternal age’ patients; YGPA) identified through the Subfertility Health Assisted Reproduction and the Environment (SHARE) cohort to investigate differences in DNA methylation. No differentially methylated regions were identified between the OGPA and YGPA groups. Further, when assessing only the sites previously shown to be altered by age, no statistically significant differences between OGPA and YGPA were identified. This was true even despite the lower bar for significance after removing multiple comparison correction in a targeted approach. Interestingly though, in an analysis of the 140 loci known to have decreased methylation with age, the majority (~ 72%) had lower methylation in OGPA compared to YGPA though the differences were extremely small (~ 1.5%). Conclusions This study suggests that the robust and consistent age-associated methylation alterations seen in human sperm are ‘reset’ during large-scale epigenetic reprograming processes and are not directly inherited trans-generationally (over two generations). An extremely small trend was present between the YGPA and OGPA groups that resemble the aging pattern in older sperm. However, this trend was not significant and was so small that, if real, is almost certainly biologically inert.

Download Full-text

Rapid sperm capture: High-throughput flagellar waveform analysis

10.1101/551267 ◽

2019 ◽

Cited By ~ 2

Author(s):

M.T. Gallagher ◽

G. Cupples ◽

E.H. Ooi ◽

J.C. Kirkman-Brown ◽

D.J. Smith

Keyword(s):

Beat Frequency ◽

Surrounding Medium ◽

Human Sperm ◽

Large Cell ◽

Waveform Analysis ◽

Mechanical Activity ◽

Natural Fertility ◽

Published Data ◽

Waveform Data ◽

Flagellar Beat

SummaryFlagella are critical across all eukaryotic life, and the human sperm flagellum is crucial to natural fertility. Existing automated sperm diagnostics (CASA) rely on tracking the sperm head and extrapolating measures. We describe fully-automated tracking and analysis of flagellar movement for large cell numbers. The analysis is demonstrated on freely-motile cells in low and high viscosity fluids, and validated on published data of tethered cells undergoing pharmacological hyperactivation. Direct analysis of the flagellar beat reveals that the CASA measure ‘beat cross frequency’, does not measure beat frequency. A new measurement, track centroid speed, is validated as an accurate differentiator of progressive motility. Coupled with fluid mechanics codes, waveform data enables extraction of experimentally intractable quantities such as energy dissipation, disturbance of the surrounding medium and viscous stresses. We provide a powerful and accessible research tool, enabling connection of the cell’s mechanical activity to its motility and effect on its environment.

Download Full-text

Intergroup Threat and Outgroup Attitudes

Social Psychology ◽

10.1027/1864-9335/a000127 ◽

2013 ◽

Vol 44 (5) ◽

pp. 311-319 ◽

Cited By ~ 12

Author(s):

Marco Brambilla ◽

David A. Butz

Keyword(s):

Gay Men ◽

Social Group ◽

Welfare Recipients ◽

Intergroup Attitudes ◽

Social Policies ◽

Intergroup Threat ◽

Economic Threat ◽

The Impact ◽

General Climate

Two studies examined the impact of macrolevel symbolic threat on intergroup attitudes. In Study 1 (N = 71), participants exposed to a macrosymbolic threat (vs. nonsymbolic threat and neutral topic) reported less support toward social policies concerning gay men, an outgroup whose stereotypes implies a threat to values, but not toward welfare recipients, a social group whose stereotypes do not imply a threat to values. Study 2 (N = 78) showed that, whereas macrolevel symbolic threat led to less favorable attitudes toward gay men, macroeconomic threat led to less favorable attitudes toward Asians, an outgroup whose stereotypes imply an economic threat. These findings are discussed in terms of their implications for understanding the role of a general climate of threat in shaping intergroup attitudes.

Download Full-text