Inhibition of bovine sperm-oocyte fusion by a monoclonal antibody recognising the TEC-2 epitope on bovine oocytes

Inhibition of bovine sperm-oocyte fusion by the p-aminophenyl derivative of D-mannose

Several steps in the process of mammalian fertilization are mediated by carbohydrates. This study investigated the role of the p-aminophenyl derivative of d-mannose (APMP) during bovine fertilization. Inseminating cumulus-oocyte complexes (COCs) in the presence of increasing APMP concentrations resulted in a significant dose-dependent decrease of the fertilization rate (P < 0.05). No negative effect of 50 mM APMP on total sperm motility and progressive motility was found. Subsequently, the fertilization steps at which this blocking effect could be exerted were investigated, i.e., sperm penetration of the cumulus oophorus, sperm-zona binding, acrosome reaction, sperm-oolemma binding, and/or sperm-oocyte fusion. Inseminating cumulus-enclosed and cumulus-denuded oocytes in the presence of 50 mM APMP significantly decreased the fertilization rate to a comparable minimum level (P < 0.05). There was no significant relationship between the number of spermatozoa bound to the zona pellucida and the APMP concentration, and APMP nor d-mannosylated bovine serum albumin (BSA) suppressed or stimulated sperm acrosomal status. Inseminating zona-free oocytes in the presence of 50 mM APMP did not influence sperm-oolemma binding, but significantly inhibited sperm-oocyte fusion (P < 0.05). Preincubating zona-free oocytes with 200 microg/ml Con A but not with 50 mM APMP inhibited the sperm-oocyte fusion rate to the same extent as when the gametes were simultaneously exposed to 50 mM APMP. These data indicate that the blocking effect of APMP on bovine fertilization is mainly due to an inhibition of sperm-oocyte fusion, probably by specific obstruction of the sperm receptor sites that are responsible for the fusion process.

Porcine oocyte activation: differing roles of calcium and pH

Intracellular pH has recently been shown to increase during parthenogenetic activation of the porcine oocyte. In the following set of experiments, intracellular pH was monitored during activation and pronuclear development was assessed following activation treatments with calcium, in the absence of calcium, and in oocytes loaded with the calcium chelator BAPTA-AM in calcium-free medium. Intracellular pH increase was not different among groups when treating with 7% ethanol or 50 microM calcium ionophore, or during treatment with thimerosal for 12 or 25 min. Activation with thimerosal (200 microM, 12 min) followed by 8 mM dithiothreitol (DTT, 30 min) resulted in a decreased pronuclear development in calcium-free medium with or without BAPTA-AM loaded oocytes as compared to controls. Activation with 50 microM calcium ionophore resulted in pronuclear development that was different between the calcium-free and BAPTA-AM loaded oocytes in calcium-free medium. Similar incidences of pronuclear formation were observed in all ethanol treatment groups. It was concluded that external calcium as well as large changes in intracellular free calcium are not necessary for the increase in intracellular pH, but normal intracellular calcium signaling is critical for normal levels of pronuclear development. Finally, oocytes were measured for intracellular pH changes for 30 min following subzonal sperm injection. Intracellular pH did not increase, although pronuclear formation was observed 6 hr post SUZI. This suggested that major differences were still present between sperm-induced and parthenogenetic activation of the porcine oocyte.

Dynamics of the mammalian sperm plasma membrane in the process of fertilization

Sexual reproduction requires the fusion of sperm cell and oocyte during fertilization to produce the diploid zygote. In mammals complex changes in the plasma membrane of the sperm cell are involved in this process. Sperm cells have unusual membranes compared to those of somatic cells. After leaving the testes, sperm cells cease plasma membrane lipid and protein synthesis, and vesicle mediated transport. Biophysical studies reveal that lipids and proteins are organized into lateral regions of the sperm head surface. A delicate reorientation and modification of plasma membrane molecules take place in the female tract when sperm cells are activated by so-called capacitation factors. These surface changes enable the sperm cell to bind to the extra cellular matrix of the egg (zona pellucida, ZP). The ZP primes the sperm cell to initiate the acrosome reaction, which is an exocytotic process that makes available the enzymatic machinery required for sperm penetration through the ZP. After complete penetration the sperm cell meets the plasma membrane of the egg cell (oolemma). A specific set of molecules is involved in a disintegrin-integrin type of anchoring of the two gametes which is completed by fusion of the two gamete plasma membranes. The fertilized egg is activated and zygote formation preludes the development of a new living organism. In this review we focus on the involvement of processes that occur at the sperm plasma membrane in the sequence of events that lead to successful fertilization. For this purpose, dynamics in adhesive and fusion properties, molecular composition and architecture of the sperm plasma membrane, as well as membrane derived signalling are reviewed.