1,720,995 research outputs found
Polarized site of sperm entrance in the egg of a freshwater bivalve, Unio elongatulus (Mollusca, Bivalvia)
No full textWe studied the organization of the egg of a freshwater bivalve, Unio elongatulus. This egg is markedly polarized. At the vegetal pole there is a crater which constitutes the point of attachment of the growing oocyte to the ovarian wall. This has previously been interpreted as a micropyle. We show that the sperm does not enter the egg through the crater but in a differentiated region around it, mostly at its base. This region is characterized by a wrinkled surface and is the only site of the vitelline coat which specifically binds the lectin from Lotus tetragonolobus. The egg reacts explosively upon fertilization, ejecting vacuolar material from the crater. The role of this "egg reaction" in relation to the prevention of polyspermy is discussed. © 1988
Antral development influences plasma membrane organization but not cortical granule distribution in mouse oocytes
No full textCarbohydrate-mediated sperm-egg interaction and species specificity: A clue from the Unio elongatulus model
No full textAs a first step fertilization requires that sperm bind to the extracellular coat of the egg. It is generally accepted that binding is mediated by complex carbohydrates on the egg coat, recognized by carbohydrate-binding proteins on the sperm surface. In the mollusc bivalve Unio elongatulus, the main functional epitope of the carbohydrate ligand has been determined, and it shares several characteristics with other sugar structures involved in the fertilization process in different animal models. A polyclonal antibody against the Unio epitope reacts with the human ZP3 glycoprotein and the Unio ligand binds human spermatozoa in an in vitro assay. These findings are discussed in the light of the species specificity of sperm-egg binding at fertilization
The role of mitochondria in energy production for human sperm motility
No full textMitochondria of spermatozoa are different from the corresponding organelles of somatic cells, in both their morphology and biochemistry. The biochemical differences are essentially related to the existence of specific enzyme isoforms, which are characterized by peculiar kinetic and regulatory properties. As mitochondrial energy metabolism is a key factor supporting several sperm functions, these organelles host critical metabolic pathways during germ cell development and fertilization. Furthermore, spermatozoa can use different substrates, and therefore activate different metabolic pathways, depending on the available substrates and the physico-chemical conditions in which they operate. This versatility is critical to ensure fertilization success. However, the most valuable aspect of mitochondria function in all types of cells is the production of chemical energy in the form of ATP which can be used, in the case of spermatozoa, for sustaining sperm motility. The latter, on the other hand, represents one of the major determinants of male fertility. Accordingly, the presence of structural and functional alterations in mitochondria from asthenozoospermic subjects confirms the important role played by these organelles in energy maintenance of sperm motility. The present study gives an overview of the current knowledge on the energy-producing metabolic pathways operating inside human sperm mitochondria and critically analyse the differences with respect to somatic mitochondria. Such a comparison has also been carried out between the functional characteristics of human sperm mitochondria and those of other mammalian species. A deeper understanding of mitochondrial energy metabolism could open up new avenues of investigation in bioenergetics of human sperm mitochondria, both in physiological and pathological conditions
Oxygen uptake by mitochondria in demembranated human spermatozoa: a reliable tool for the evaluation of sperm respiratory efficiency
No full textIn this work we report a relatively simple and fast method for analyzing oxygen consumption and therefore mitochondrial functionality, in individual human ejaculates. This oxygraphic method requires a low number of cells, is highly reproducible and linearly correlates with sperm concentration. Our results showed that oxygen uptake by mitochondria of demembranated sperm cells is significantly stimulated by respiratory substrates and ADP. The RCR values indicate a good coupling between respiration and phosphorylation by sperm mitochondria and thus a well preserved integrity of the mitochondria themselves. Interestingly, whereas the rates of oxygen uptake (V3 and V4), as expected, changed with different sperm concentrations, the RCR values remained constant thus demonstrating a linear response of the assay. The results obtained with the use of a panel of specific inhibitors of the respiratory chain suggested that this method, besides its potential clinical application, can also be useful for a deeper understanding of the biochemical properties of sperm mitochondria and their role in ATP production in human spermatozoa
Oxygen uptake by mitochondria in demembranated human spermatozoa: A reliable tool for the evaluation of sperm respiratory efficiency
No full textIn this work we report a relatively simple and fast method for analysing oxygen consumption and therefore mitochondrial functionality, in individual human ejaculates. This oxygraphic method requires a low number of cells, is highly reproducible and linearly correlates with sperm concentration. Our results have shown that oxygen uptake by mitochondria of demembranated sperm cells from normozoospermic subjects is significantly stimulated by a large set of respiratory substrates and ADP. The respiratory control ratio (RCR) values indicate a good coupling between respiration and phosphorylation by sperm mitochondria and thus a well preserved integrity of the mitochondria themselves. Interestingly, whereas the rates of oxygen uptake, as expected, changed with different sperm concentrations, the RCR values remained constant, thus demonstrating a linear response of the assay. In asthenozoospermic subjects, however, a significant decrease in the sperm respiratory efficiency was found. In our opinion, the implications of this study are the following. On the one hand, a careful and detailed investigation of the mitochondrial bioenergetics of sperm will provide more insight into the basic biology of the spermatozoon with the aim of obtaining more information on the role of sperm mitochondria in motility and on the overall quality of the gametes. On the other hand, we are confident that this relatively simple and fast assay, requiring a limited amount of sperm cells, can be used as a routine semen analysis in clinical investigation
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