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Sara Rubinstein

Publications and source records attributed to Sara Rubinstein.

5 recordsLinked to original sources
PubMed2006

Loading magnetic nanoparticles into sperm cells does not affect their functionality.

The spontaneous loading of magnetite nanoparticles into sperm cell was carried out by mixing an aqueous colloidal solution of Fe3O4-PVA with sperm cells (10(8) cells/ml) for 2 h at 37 degrees C suspended in glucose-free modified Tyrode solution. The penetration of the magnetite nanoparticles into the sperm cells was monitored by conventional analytical chemistry. We have demonstrated that the motility and the ability to undergo the acrosome reaction (i.e., the ability to fertilize the egg) were not affected by the presence of the magnetite nanoparticles.

Journal Article↗
PubMed2005

Role of actin cytoskeleton in mammalian sperm capacitation and the acrosome reaction.

In order to fertilize, the mammalian spermatozoa should reside in the female reproductive tract for several hours, during which they undergo a series of biochemical modifications collectively called capacitation. Only capacitated sperm can undergo the acrosome reaction after binding to the egg zona pellucida, a process which enables sperm to penetrate into the egg and fertilize it. Polymerization of globular (G)-actin to filamentous (F)-actin occurs during capacitation, depending on protein kinase A activation, protein tyrosine phosphorylation, and phospholipase D activation. F-actin formation is important for the translocation of phospholipase C from the cytosol to the sperm plasma membrane during capacitation. Prior to the occurrence of the acrosome reaction, the F-actin should undergo depolymerization, a necessary process which enables the outer acrosomal membrane and the overlying plasma membrane to come into close proximity and fuse. The binding of the capacitated sperm to the zona pellucida induces a fast increase in sperm intracellular calcium, activation of actin severing proteins which break down the actin fibers, and allows the acrosome reaction to take place.

Acrosome Reaction↗
PubMed2003

Remodeling of the actin cytoskeleton during mammalian sperm capacitation and acrosome reaction.

The sperm acrosome reaction and penetration of the egg follow zona pellucida binding only if the sperm has previously undergone the poorly understood maturation process known as capacitation. We demonstrate here that in vitro capacitation of bull, ram, mouse, and human sperm was accompanied by a time-dependent increase in actin polymerization. Induction of the acrosome reaction in capacitated cells initiated fast F-actin breakdown. Incubation of sperm in media lacking BSA or methyl-beta-cyclodextrin, Ca(2+), or NaHCO(3), components that are all required for capacitation, prevented actin polymerization as well as capacitation, as assessed by the ability of the cells to undergo the acrosome reaction. Inhibition of F-actin formation by cytochalasin D blocked sperm capacitation and reduced the in vitro fertilization rate of metaphase II-arrested mouse eggs. It has been suggested that protein tyrosine phosphorylation may represent an important regulatory pathway that is associated with sperm capacitation. We show here that factors known to stimulate sperm protein tyrosine phosphorylation (i.e., NaHCO(3), cAMP, epidermal growth factor, H(2)O(2), and sodium vanadate) were able to enhance actin polymerization, whereas inhibition of tyrosine kinases prevented F-actin formation. These data suggest that actin polymerization may represent an important regulatory pathway in with sperm capacitation, whereas F-actin breakdown occurs before the acrosome reaction.

Acrosome Reaction↗
PubMed2002

Extracellular adenosine triphosphate stimulates acrosomal exocytosis in bovine spermatozoa via P2 purinoceptor.

The presence of ATP in the genital tract fluid of mammals provokes questions regarding its function in the fertilization process. We investigated the effect of extracellular ATP (ATPe) on the activation of bovine spermatozoa. A signal transduction mechanism for ATP involving the receptor-mediated release of second messengers is described. Treatment of spermatozoa with ATP, uridine triphosphate (UTP), or 2-methylthio-ATP resulted in a concentration-dependent increase of acrosomal exocytosis, whereas treatment with either AMP or adenosine induced little exocytosis. This suggested that the receptor involved is of the P2 and not the P1 type. Several lines of evidence also suggest that the ATP purinoceptor is of the P2y and not the P2x type. First, the acrosome reaction was induced by the P2y-agonists ATP, UTP, or 2-methylthio-ATP, but no effects were shown by the P2x-agonists alpha,beta-methylene-ATP or beta,gamma-methylene-ATP. Second, ATP-induced acrosomal exocytosis was inhibited by the P2y antagonists, but not by the P2x antagonists. Third, enhanced Ca2+ uptake into the cells was observed with ATP and 2-methylthio-ATP, but not with beta,gamma-methylene-ATP. Additionally, ATP induced elevation of intracellular Ca2+ and cAMP, and the effect on cAMP was predominantly enhanced by including Ca2+ and the Ca2+-ionophore A23187 in the incubation medium. Extracellular ATP also activates protein kinase Calpha (PKCalpha), and the acrosome reaction, stimulated by ATPe, is inhibited by a PKC-specific inhibitor. In summary, we suggest that ATPe activates the P2 purinoceptor that elevates [Ca2+]i, which leads to PKCalpha activation and culminates in acrosomal exocytosis.

Acrosome↗