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J E Faure

Publications and source records attributed to J E Faure.

6 recordsLinked to original sources
PubMed2001

Double fertilization in flowering plants: discovery, study methods and mechanisms.

The double fertilization of flowering plants was discovered a century ago. The cytology of the gametes is now well known. However the description of the fertilization steps is still poor and most of the cellular and molecular mechanisms involved are unknown. Recent research using in vitro fertilization demonstrated that the early steps of fertilization share some homology with those in animal species. In particular, gamete fusion is followed by a cytosolic calcium increase in the fertilized egg as well as a calcium influx. Further understanding of fertilization also comes from the analysis of mutants isolated in Arabidopsis thaliana. Important new ideas have already emerged from these studies such as the importance of the female gametophyte in embryo development, and an early silencing of the male genome during the first days following gamete fusion.

Arabidopsis↗
PubMed2001

Differential contribution of cytoplasmic Ca2+ and Ca2+ influx to gamete fusion and egg activation in maize.

In multicellular organisms, gamete fusion triggers a set of events, collectively known as egg activation, that leads to the development of a new individual. Every species that has been studied shows at least one rise in cytoplasmic Ca2+ concentration ([Ca2+]Cyt) after gamete fusion which is believed to be involved in activation. Yet the source and regulation of this Ca2+ signal and the way it is transduced inside the zygote are controversial. In higher plants, in vitro fertilization (IVF) has enabled the description of a rise in [Ca2+]Cyt (ref. 4) that is sufficient for activation, and of a Ca2+ influx that spreads as a wavefront from the fusion site The relationship between these two responses is unknown. Using a new combination of methods that simultaneously monitor the extracellular flux with a Ca2+-vibrating probe, and [Ca2+]Cyt by widefield imaging, we directly determined that the Ca2+ influx precedes the [Ca2+]Cyt elevation by 40-120 s. In addition, results from experiments using the Ca2+-channel inhibitor gadolinium (Gd3+) suggest that the Ca2+ influx may be necessary for sperm incorporation. We also present evidence for a putative sperm-dependent Gd3+-insensitive localized Ca2+ influx confined to the fusion point.

Calcium Channel Blockers↗
PubMed2000

A calcium influx is triggered and propagates in the zygote as a wavefront during in vitro fertilization of flowering plants.

In this paper, we report direct measurement of an influx of extracellular Ca(2+) induced by gamete fusion in flowering plants. This result was obtained during maize in vitro fertilization with the use of an extracellular Ca(2+)-selective vibrating probe. Ca(2+) influx recorded at the surface of isolated egg cells, with or without adhesion of a male sperm cell, was close to zero and stable over time. Gamete fusion, however, triggered a Ca(2+) influx in the vicinity of the sperm entry site with a delay of 1.8 +/- 0.6 sec. The Ca(2+) influx spread subsequently through the whole egg cell plasma membrane as a wavefront, progressing at an estimated rate of 1.13 micrometer.(-1). Once established, Ca(2+) influx intensities were sustained, monotonic and homogeneous over the whole egg cell, with an average peak influx of 14.92 pmol .cm(-2).(-1) and an average duration of 24.4 min. The wavefront spread of channel activation correlates well with the cytological modifications induced by fertilization, such as egg cell contraction, and with the cytosolic Ca(2+) ((c)[Ca(2+)]) elevation previously reported. Calcium influx was inhibited effectively by gadolinium, possibly implicating mechanosensitive channels. Furthermore, artificial influxes created by incubation with Ca(2+) ionophores mimicked some aspects of egg activation. Taken together, these results suggest that, during fertilization in higher plants, gamete membrane fusion starts the first embryonic events by channel opening and Ca(2+) influx. In turn, (c)[Ca(2+)] may work as a trigger and possibly a space and time coordinator of many aspects of egg activation.

Calcium↗
PubMed1999

The frequency of calcium oscillations in mouse eggs at fertilization is modulated by the number of fused sperm.

In a variety of calcium signaling systems, the frequency of intracellular calcium oscillations is physiologically important. Probably multiple factors control the frequency of calcium oscillations in the egg after fertilization and many of these remain to be identified. In this study, we present the first rigorous set of data showing that monospermic fertilization is important for setting the physiological calcium oscillation frequency. Recordings in 152 zona-free eggs show that the general pattern of the calcium oscillations is identical in monospermic and polyspermic eggs; however, the oscillation frequency is higher in polyspermic eggs (P < 10(-6)). The frequency of the late oscillations increases with the number of sperm heads incorporated: 5.2 +/- 0.3 spikes per hour (mean +/- SEM; n = 55) in monospermic eggs, 6.6 +/- 0.3 (n = 62) in dispermic eggs, 8.7 +/- 0.7 (n = 23) in trispermic eggs, and 8.9 +/- 0.9 (n = 12) in eggs with four or more sperm heads. The frequency of the early oscillations is also increased in polyspermic eggs. Seventy-eight additional eggs were divided into two groups and inseminated with two different sperm concentrations ("low" and "high") to obtain one group mainly monospermic and the other mainly polyspermic. The two groups of eggs oscillated at different frequencies (P < 10(-5)). These data rule out the possibility of an egg effect in which some eggs would have the dual properties of oscillating faster and of being able to fuse with several sperm cells. These data instead suggest that the sperm modulates the frequency of the oscillations in a dose-dependent manner.

Animals↗
PubMed1998

Fertilization defects in sperm from mice lacking fertilin beta.

Fertilin, a member of the ADAM family, is found on the plasma membrane of mammalian sperm. Sperm from mice lacking fertilin beta were shown to be deficient in sperm-egg membrane adhesion, sperm-egg fusion, migration from the uterus into the oviduct, and binding to the egg zona pellucida. Egg activation was unaffected. The results are consistent with a direct role of fertilin in sperm-egg plasma membrane interaction. Fertilin could also have a direct role in sperm-zona binding or oviduct migration; alternatively, the effects on these functions could result from the absence of fertilin activity during spermatogenesis.

ADAM Proteins↗