Amphibian Fertilization Research Articles

Sperm-Force: Naturphilosophie and George Newport's Quest to Discover the Secret of Fertilization.

This paper analyses the forgotten concept of "sperm-force" proposed by George Newport (1803-1854). Newport is known for his comprehensive microscopic examinations of sperm and egg interaction in amphibian fertilization between 1850 and 1854. My work with archival sources reveals that Newport believed fertilization was caused by sperm-force, which the Royal Society refused to publish. My reconstruction chronologically traces the philosophical and experimental origins of sperm-force to Newport's 1830s entomological work. Sperm-force is a remnant of Newport's speculations on the creation of the active individual. I argue that sperm-force was rooted in British interpretations of German Naturphilosophie, which demonstrates Continental influences on mid-Victorian embryology, particularly the role of male generative power. This context provides further evidence that British versions of Romantic science fostered sophisticated experimental work. The refusal by Paleyite stalwarts of natural theology to publish Newport's ideas illustrates the institutional resistance to German pantheistic and vitalistic influences. This reconstruction of sperm-force's philosophical foundation and its reception offers new understandings of mid-Victorian attitudes toward the inheritance of mind and body. It situates Newport's work within the nineteenth century's scientific project to assign stereotypical genders to the gametes.

SPERM FACTORS AND EGG ACTIVATION: Divergent sperm factors for egg activation in amphibian fertilization.

Mature amphibian eggs arrested at meiotic metaphase II must undergo activation to initiate embryonic development soon after fertilization. Fertilizing sperm provide eggs with a signal that induces egg activation, and an increase in intracellular Ca2+ concentration in the egg cytoplasm (a Ca2+ rise) is the most important signal for this initiation. The sperm transmits the signal for the Ca2+ rise, known as the sperm factor, which is divergent between anurans and urodeles. In monospermic anurans, the sperm transmits the signal through a receptor on the egg membrane, causing a single rapid Ca2+ rise. Sperm matrix metalloproteinase-2 is a potential candidate for the receptor-mediated sperm factor in anurans. In physiologically polyspermic urodeles, multiple slower Ca2+ rises are caused by a soluble sperm factor (sperm-specific citrate synthase) which is transferred to the egg cytoplasm after sperm-egg fusion. We discuss the molecular mechanisms of egg activation in amphibian fertilization, focusing on recent progress in characterizing these sperm factors and their divergence during the evolution of tetrapod vertebrates.

A Novel Cysteine Knot Protein for Enhancing Sperm Motility That Might Facilitate the Evolution of Internal Fertilization in Amphibians.

Internal fertilization ensures successful reproduction of tetrapod vertebrates on land, although how this mode of reproduction evolved is unknown. Here, we identified a novel gene encoding sperm motility-initiating substance (SMIS), a key protein for the internal fertilization of the urodele Cynops pyrrhogaster by Edman degradation of an isolated protein and subsequent reverse transcription polymerase chain reaction. The SMIS gene encoded a 150 amino-acid sequence including the cysteine knot (CK) motif. No gene with substantial similarity to the SMIS was in the data bank of any model organisms. An active site of the SMIS was in the C-terminal region of the 2nd loop of CK motif. A synthetic peptide including the active site sequence bound to the midpiece and initiated/enhanced the circular motion of C. pyrrhogaster sperm, which allows penetration of the egg jelly specialized for the internal fertilization of this species. The synthetic peptide bound to whole sperm of Rhacophorus arboreus and enhanced the rotary motion, which is adapted to propel the sperm through egg coat matrix specialized for arboreal reproduction, while it bound to the tip of head and tail of Bufo japonicus sperm, and enhanced the vibratory motion, which is suited to sperm penetration through the egg jelly specialized for the reproduction of that species in freshwater. The polyclonal antibody against the active site of the SMIS specifically bound to egg coat matrix of R. arboreus. These findings suggest that diversification of amphibian reproductive modes accompanies the specialization of egg coat and the adaptation of sperm motility to penetrate the specialized egg coat, and SMIS acts as the sperm motility enhancer of anurans and urodeles that might facilitate to adaptively optimize sperm motility for allowing the establishment of internal fertilization.

In silico identification of the genes for sperm-egg interaction in the internal fertilization of the newt Cynops pyrrhogaster.

A specific sperm-egg interaction in the oviductal matrix is crucial for internal fertilization of the red-bellied newt, Cynops pyrrhogaster. An understanding of the molecular basis of this interaction is expected to elucidate the evolutionary history of internal fertilization in amphibians. Recently, deep sequencing technology has provided global gene information even in nonmodel animals, allowing us to understand specific features of the molecular mechanisms underlying fertilization in C. pyrrhogaster. In the present study, we screened de novo assembled RNAseq from ovary, testis, and oviduct samples in C. pyrrhogaster and identified the base sequences encoding zona pellucida (ZP) proteins, voltage-dependent Ca(2+) channels, and cysteine-rich secretory proteins (CRISPs), which respectively are sperm receptors for egg envelopes, major mediators of sperm intracellular signaling, and expected extracellular modulators for sperm function in the female reproductive tract. In the ovary, ZP homologues of all six subgroups were found, including a ZP1 homologue that was newly found in amphibians, a ZP4 homologue, and six ZPC homologues. The unique combination of ZP proteins suggests a new mechanism for sperm binding to egg envelopes in the internal fertilization of C. pyrrhogaster. In the testis, CaV1.1, 1.2, and 3.2, which are L- and T-type voltage-dependent Ca(2+) channels, were found as potential mediators for the internal fertilization-specific sperm-egg interaction. We also found CRISP 2 in the oviduct, which is speculated to participate in the sperm-egg interaction. These results indicate that the de novo assembled RNAseq is a powerful tool allowing analysis of the specific sperm-egg interactions in C. pyrrhogaster.

61. Cholesterol depletion affects the biophysical state of oocyte membranes disturbing amphibian fertilization

The steroid hormone progesterone induces the resumption of meiosis of full-grown ovarian oocytes arrested at the first meiotic division. Apart from protein-mediated signaling, progesterone-induced maturation involves enzyme activations that modify membrane fluidity and release a cascade of lipid messengers. Once the oocyte is mature, it enters meiosis II and spontaneously arrests in metaphase until fertilization, in which drastic membrane reorganization occurs when amphibian sperm fuses with the oocyte membrane and exocytosis of cortical granules takes place. The predominant lipids in most membranes are phospholipids and cholesterol. Cholesterol stabilizes membranes at low temperatures and it is an important constituent of membrane rafts. In this study, the cholesterol-binding drug methyl-β-cyclodextrin (MβCD) was used for cholesterol modulation in order to assess membrane raft involvement in amphibian fertilization. The generalized polarization (GP) of the fluorescent probe Laurdan was used to study the effect of cholesterol depletion and fertilization on the biophysical properties of membranes from Rhinella arenarum oocytes evaluated in temperatures ranging from 5 °C to 40 °C. For comparative reasons, cholesterol removal of ovarian oocytes and progesterone-induced maturation were also analyzed. As it was expected for native membranes of complex lipid composition, GP values gradually decreased when temperature increased. Light (L) and Heavy (H) membranes, enriched in rafts and non-raft plasma membrane, respectively, showed two different thermotropic profiles of GP. GP values were higher in L fraction with respect to H indicating a higher membrane lipid order in agreement with the enrichment in cholesterol of these low-density membranes. Cholesterol depletion of ovarian oocytes, mediated by MβCD, caused a decrease in the GP value of L membranes which corresponds to a greater penetration of water molecules and indicates a decrease in membrane lipid order. In contrast, GP values of H membranes increased after MβCD treatment. As a result, both plasma membrane fractions become more similar in their biophysical states. On the other hand, progesterone modified the biophysical properties of the plasma membrane increasing the lipid order of both fractions. Interestingly, different to ovarian oocytes, membranes isolated from ovulated oocytes showed an important lipid order resistance to variations in temperature. In these oocytes, MβCD treatment also decreased lipid order of L membranes but at a lesser extent than ovarian oocytes. In addition, fertilization increased lipid order of non-raft membranes. As we have previously shown for progesterone-induce maturation, functional studies revealed that MβCD treatment inhibited fertilization in a dose-dependent manner. Cholesterol repletion performed using MβCD pre-loaded with cholesterol induced a recovery of the fertilization rate. These results indicate that fertilization competence of amphibian oocytes is sensitive to the cholesterol content of both plasma membrane fractions. Taking into account that the plasma membrane is a major site of cryoinjury during cryopreservation of mammalian oocytes, these results open a discussion on sterol modulation to be able to obtain a stable source of oocytes available for in vitro fertilization and other related biotechnologies.

Ooplasm segregation in the squid embryo, Loligo pealeii.

Ooplasm segregation in the squid embryo, Loligo pealeii.

Potential involvement of C 3 complement factor in amphibian fertilization

We have assessed the potential involvement of C 3, the third complement factor, and its receptor in Bufo arenarum fertilization. We show that a polyclonal antibody against a B. arenarum C 3-like factor (C 3 Ba) reacts specifically with components of the extracellular matrix (ECM) of coelomic eggs and the cell membrane of uterine eggs. Interestingly, we have identified a 163 kD protein immunoreactive with a monoclonal antibody against the CD11b α chain of the human C 3 receptor on the cell membrane of the animal pole of uterine eggs, the site of entry of the sperm, but not in coelomic eggs (CR3 Ba). Treatment of coelomic eggs with a pars recta oviductal-like protease, trypsin, induced the translocation of C 3 Ba from the ECM to the cell membrane. Furthermore, inhibition of CR3 Ba by trypan blue, as well as inhibition of C 3 Ba by anti-C 3 Ba on uterine eggs impaired fertilization, whereas identical treatment on sperm cells did not alter percentage fertilization. Our results suggest, (A) that changes in the localization of C 3 Ba from the ECM to the cell membrane may be triggered by trypsin-like proteases during passage of eggs through the oviduct; and (B) that C 3 Ba/CR3 Ba may be involved in B. arenarum fertilization.

Mechanisms of Egg Activation and Polyspermy Block in Amphibians and Comparative Aspects with Fertilization in Other Vertebrates

Abstract For precise temporal activation of the egg during amphibian fertilization, the sperm must provide a signal for egg activation at the time of membrane binding or fusion between sperm and eggs. A fertilizing sperm causes a Ca2+ wave which is both necessary and sufficient for egg activation at amphibian fertilization. The Ca2+ wave seems to be mediated by IP3-receptors on the endoplasmic reticulum and by IP3 produced by hydrolysis of PLC activated by a Src-related protein tyrosine kinase (Xyk) in Xenopus eggs. We have proposed three different hypotheses for initiation of egg activation in amphibian eggs: the Ca2+-influx model, the membrane receptor model, and the soluble factor model. The membrane receptor model and the soluble factor model seems to be applied to the monospermic Xenopus fertilization and the physiologically polyspermic Cynops fertilization, respectively. The Ca2+ wave at egg activation induces a positive fertilization potential which prevents entry of a second sperm in fertilization...

Effect of mercuric chloride on fertilization and larval development in the river frog, Rana heckscheri (Wright) (Anura: Ranidae)

Previous investigations have indicated that heavy metals such as copper, cadmium, lead and mercury can act as systemic toxicants in many species of wildlife. Although numerous studies have emphasized the effects of metals and pesticides on metabolism, growth, survivorship, neural processes and reproduction in a number of taxa, little information is available on the effects of sublethal concentrations of metals on the reproductive physiology of amphibians. Industrial processes and mining activities can release substantial concentrations of heavy metals such as mercury into aquatic habitats. Since most amphibians have obligate aquatic larval stages, they are exposed to pollutants discharged into the aquatic environment. Amphibians can act as accumulators of heavy metals and their larval stages are useful indicators of pollution levels in the field. What little data are available, indicate that metals can significantly reduce viability in amphibians through their actions on metabolism, development and gametogenesis. The recent concerns over worldwide declines in amphibian populations and the susceptibility of amphibian populations to environmental toxicants, led me to assess the effect of mercuric chloride, one of the most common and persistent toxicants in aquatic environments, on fertilization and larval development in the river frog, Rana heckscheri (Wright). Although there is some informationmore » on fish, very little data are available on the effects of mercury on fertilization in amphibians generally, and no published data exist for R. heckscheri. This species is a conspicuous component of the aquatic fauna of parts of the southeastern United States where mercury levels have increased significantly over the last two decades. 22 refs., 2 tabs.« less

Fertilization in Amphibians: The Ancestry of the Block to Polyspermy

Publisher Summary Amphibians exhibit both styles of fertilization: monospermy and polyspermy. Monospermy is confined to tailless frogs and toads that comprise the order Anura, while physiological polyspermy is found in the tailed newts and salamanders of the order Urodela. This chapter reviews the process of fertilization in amphibians, particularly as it relates to polyspermy. The chapter discusses ways to explore the nature of the cytological ancestry. Amphibians exhibit a great diversity of reproductive patterns. This diversity makes the amphibians ideal animals for examining the cellular evolution of developmental processes. Fertilization in anurans and urodeles is so different that it represents an important character distinguishing the orders. Comparison between fertilization in anurans and urodeles shows a mirror image dichotomy with respect to polyspermy. The anuran egg has a fast and slow block to polyspermy, and it has no protection when more than one sperm enters. On the other hand, the urodele egg lacks both external blocks to polyspermy but can deal with accessory nuclei within the egg. The arrangement of components in the membranes and in the cortical granules is considered important for the polyspermy-blocking reactions.

Effect of Phosphatidylcholine on Acrosome Breakdown and Fertilizing Capacity of Amphibian Spermatozoa: (phosphatidylcholine vesicles/amphibian fertilization/acrosome breakdown).

The effect of vesicles of purified egg yolk phosphatidylcholine on the fertilizing capacity and acrosome breakdown of amphibian spermatozoa was studied. When Bufo arenarum spermatozoa were incubated with either small unilamellar vesicles (prepared by sonication) or with large unilamellar vesicles (prepared by reverse-phase evaporation) a decrease in the fertilizing capacity of spermatozoa was found. At the same phosphatidylcholine concentration, large unilamellar vesicles were more inhibitory than small unilamellar vesicles. The inhibition was dependent upon the phospholipid concentration and the length of the incubation period. Small unilamellar vesicles did not modify the time course of acrosome breakdown in Leptodactylus chaquensis, while large unilamellar vesicles markedly accelerated the rate of acrosome breakdown. In both biossays, the charge of the vesicles (made either positive or negative by the addition of 5% stearylamine or 5% phosphatidic acid) did not influence their biological effect. Multilamellar vesicles did not alter the fertilizing capacity nor the acrosome breakdown. We conclude that the size and the structure of the vesicles are important parameters in determining the inhibitory capacity of phosphatidyl choline on amphibian fertilization.

Early Events in Anuran Amphibian Fertilization: An Ultrastructural Study of Changes Occurring in the Course of Monospermic Fertilization and Artificial Activation: (anuran/egg cortex/exocytosis/fertilization/microvilli).

In unfertilized frog eggs, the plasma membrane displays an animal vegetal polarity characterized by the presence of short microvilli in the vegetal hemisphere and long microvilli or ridge-like protrusions in the animal hemisphere. The densities of microvilli are similar in the two hemispheres. The fertilizing sperm always fuses with the animal hemisphere of the egg and induces a wave of exocytosis of cortical granules from its site of penetration. Similar spreading of the cortical reaction is seen on activation by pricking the egg cortex. The integration of the cortical granule membrane with the plasma membrane is rapidly followed by elongation of microvilli, which is progressively realized all over the egg surface from the site of sperm entry or the site of pricking. At this time, the length and shape of the microvilli in the animal and vegetal hemispheres are similar and their densities are the same as in unfertilized eggs. A "smoothing" wave can be seen on the living egg, 40-60 seconds after pricking, starting around the site of pricking. This wave of microvillar elongation is accompanied by changes in intensity of diffracted light spots observed at the surface of the egg. This pattern might result from rapid and progressive thickening of the cortex that would drive pigment granules into the cytoplasm. The Brownian movement of these granules is thought to be responsible for the observed diffracted light spots. Electrical stimulus or the ionophore A23187 induced activation reactions similar to those triggered by the sperm or by pricking, except that the cortical reaction began simultaneously in several distinct sites of the cortex.

Effect of trypsin inhibitors and concanavalin A on the fertilization of Bufo arenarum coelomic oocytes.

The effect of trypsin inhibitors (obtained from soybean, lima bean and ovomucoid) and Concanavalin A on fertilization in Bufo arenarum was tested. In order to study the effect of these substances at the level of the vitelline envelope of the oocytes, a new bioassay was designed. This bioassay employs coelomic oocytes to which some oviducal factors necessary for their fertility was added. Trypsin inhibitors block both the lytic effect of the acrosomal proteases on the vitelline envelope and fertilization. This indicates that the blockade of fertilization is a consequence of the inhibition of the lytic effect of the acrosomal proteases. Concanavalin A is effective as well in blocking the lytic effect of acrosomal proteases and fertilization. These effects are reversed by some sugar antagonists of the lectin, thus indicating that the effect of Concanavalin A is through its saccharide-binding capacity. These results suggested the involvement of glucosidic residues of the vitelline envelope in amphibian fertilization (the saccharide residues might be involved in the attack of the vitelline envelope by the acrosomal proteases). The possible mechanism of action of these substances is discussed.