Activation of sperm EGFR by light irradiation is mediated by reactive oxygen species

Applications of laser technology in the manipulation of human spermatozoa

The application of laser technology in the field of assisted reproductive technology (ART) has experienced rapid growth over the past decades owing to revolutionary techniques such as intracytoplasmic sperm injection (ICSI), preimplantation genetic testing (PGT), and in vitro manipulation of gametes and embryos. For male gametes, in vitro manipulation techniques include spermatozoa selection, sorting, immobilization, and quality assessment. A number of studies have been conducted to investigate the application of different laser technologies in the manipulation of human spermatozoa. However, there is a lack of a unified understanding of laser application in the in vitro manipulation of sperm and safety considerations in ART and, subsequently, the inability to make clear and accurate decisions on the clinical value of these laser technologies. This review summarizes the advancements and improvements of laser technologies in the manipulation of human spermatozoa, such as photobiomodulation therapy, laser trap systems for sperm analysis and sorting, laser-assisted selection of immotile sperm and laser-assisted immobilization of sperm prior to ICSI. The safety of those technologies used in ART is also discussed. This review will provide helpful and comprehensive insight into the applications of laser technology in the manipulation of human spermatozoa.

The interplay of ROS and the PI3K/Akt pathway in autophagy regulation

Autophagy causes the breakdown of damaged proteins and organelles to their constituent components. The phosphatidylinositol 3-kinase (PI3K) pathway played an important role in regulating the autophagic response of cells in response to changing reactive oxygen species (ROS) levels. The PI3K α catalytic subunit inhibits autophagy, while its β catalytic subunit promotes autophagy in response to changes in ROS levels. The downstream Akt protein acts against autophagy initiation in response to increases in ROS levels under nutrient-rich conditions. Akt acts by activating a mechanistic target of the rapamycin complex 1 (mTORC1) and by arresting autophagic gene expression. The AMP-activated protein kinase (AMPK) protein counteracts the Akt actions. mTORC1 and mTORC2 inhibit autophagy under moderate ROS levels, but under high ROS levels, mTORC2 can promote cellular senescence via autophagy. Phosphatase and tensin homolog (PTEN) protein are the negative regulators of the PI3K pathway, and it has proautophagic activities. Studies conducted on cells treated with flavonoids and ionizing radiation showed that the moderate increase in ROS levels in the flavonoid-treated groups corresponded with higher PTEN levels and lowered Akt levels leading to a higher occurrence of autophagy. In contrast, higher ROS levels evoked by ionizing radiation caused a lowering of the incidence of autophagy.

RNA element discovery from germ cell to blastocyst

Recent studies have shown that tissue-specific transcriptomes contain multiple types of RNAs that are transcribed from intronic and intergenic sequences. The current study presents a tool for the discovery of transcribed, unannotated sequence elements from RNA-seq libraries. This RNA Element (RE) discovery algorithm (REDa) was applied to a spectrum of tissues and cells representing germline, embryonic, and somatic tissues and examined as a function of differentiation through the first set of cell divisions of human development. This highlighted extensive transcription throughout the genome, yielding previously unidentified human spermatogenic RNAs. Both exonic and novel X-chromosome REs were subject to robust meiotic sex chromosome inactivation, although an extensive de-repression occurred in the post-meiotic stages of spermatogenesis. Surprisingly, 2.4% of the 10,395 X chromosome exonic REs were present in mature sperm. Transcribed genomic repetitive sequences, including simple centromeric repeats, HERVE and HSAT1, were also shown to be associated with RE expression during spermatogenesis. These results suggest that pervasive intergenic repetitive sequence expression during human spermatogenesis may play a role in regulating chromatin dynamics. Repetitive REs switching repeat classes during differentiation upon fertilization and embryonic genome activation was evident.

Signaling pathways involved in human sperm hyperactivated motility stimulated by Zn2

To fertilize the egg, sperm cells must reside in the female reproductive tract for several hours during which they undergo chemical and motility changes collectively called capacitation. During capacitation, the sperm develop a unique type of motility known as hyperactivated motility (HAM). The semen contains Zn²⁺ in millimolar concentrations, whereas in the female reproductive tract the concentration is around 1 µM. In this study, we characterize the role of Zn ²⁺ in human sperm capacitation focusing on its effect on HAM. Western blot analysis revealed the presence of G protein-coupled receptor 39 (GPR39) type Zn-receptor localized mainly in the sperm tail. Zn ²⁺ at micromolar concentration stimulates HAM, which is mediated by a cascade involving GPR39-AC-cAMP-PKA-Src-EGFR and phospholipase C. Both the transmembrane adenylyl cyclase (AC) and the soluble-AC are involved in the stimulation of HAM by Zn ²⁺ . The development of HAM is precisely regulated by cyclic adenosine monophosphate, in which relatively low concentration (5-10 µM) stimulated HAM, whereas at 30 µM no stimulation occurred. A similar response was seen when different concentrations of Zn ²⁺ were added to the cells; low Zn ²⁺ stimulated HAM, whereas at relatively high Zn ²⁺ , no effect was seen. We further demonstrate that the Ca ²⁺ -channel CatSper involved in Zn ²⁺ -stimulated HAM. These data support a role for extracellular Zn ²⁺ acting via GPR39 to regulate signaling pathways in sperm capacitation, leading to HAM induction.

High throughput small RNA and transcriptome sequencing reveal capacitation-related microRNAs and mRNA in boar sperm

Background

Capacitation, a prerequisite for oocyte fertilization, is a complex process involving series of structural and functional changes in sperms such as membrane modifications, modulation of enzyme activities, and protein phosphorylation. In order to penetrate and fertilize an oocyte, mammalian sperms must undergo capacitation. Nevertheless, the process of sperm capacitation remains poorly understood and requires further elucidation. In the current study, via high throughput sequencing, we identified and explored the differentially expressed microRNAs (miRNAs) and mRNAs involved in boar sperm capacitation.

Results

We identified a total of 5342 mRNAs and 204 miRNAs that were differentially expressed in fresh and capacitated boar sperms. From these, 12 miRNAs (8 known and 4 newly identified miRNAs) and their differentially expressed target mRNAs were found to be involved in sperm capacitation-related PI3K-Akt, MAPK, cAMP-PKA and Ca²⁺signaling pathways.

Conclusions

Our study is first to provide the complete miRNA and transcriptome profiles of boar sperm. Our findings provide important insights for the understanding of the RNA profile in boar sperm and future elucidation of the underlying molecular mechanism relevant to mammalian sperm capacitation.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5132-9) contains supplementary material, which is available to authorized users.