Investigation of assisted fertilization and biology of reproduction by sperm microinjection

Recent success in assisted fertilization mainly depended on the development of sperm microinjection methods: intracytoplasmic sperm injection and subzonal insemination. Some basic mechanisms that under-lie fertilization were revealed by using intracytoplasmic sperm injection. In respect to this, problems of fertility, oocyte activation, formation of pronuclei and practical aspects of intracytoplasmic sperm injection are discussed.     

From oocyte maturation to the in vitro cell cycle: the history of discoveries of Maturation-Promoting Factor (MPF) and Cytostatic Factor (CSF)

This article briefly reviews the classical cell cycle studies using oocytes and zygotes of mainly amphibians in the past century. The discussions are focused on the investigations into the cytoplasmic factors that regulate meiosis during oocyte maturation and the initiation of mitosis during fertilisation, which were carried out in the author's lab between 1967 and 1987. This chronicle traces the development of the problems and the direction in which their solutions were attempted in the course of these investigations. The author tries to answer the following questions: why he decided to study oocyte maturation, how he discovered progesterone as a maturation-inducing hormone, how he discovered and characterised the cytoplasmic regulators of the cell cycle, Maturation-Promoting Factor (MPF) and Cyto-Static Factor (CSF), and how he invented the method of observing cell cycle processes in a cytoplasmic extract in vitro.     

Quality of a stress-sensitive Cucurbita pepo L. pollen

The quality of Cucurbita pepo L. pollen was studied using field pollinations and the fluorochromatic-reaction test. The extreme sensitivity of this pollen to dehydration and ageing is demonstrated. Controlled stress applied to mature pollen leads to the development of seedless fruits. Molecular signals seem to be involved in the induction of this parthenocarpy. These results indicate the existence of distinct sequences involved in the completion of the fertilization program of pollen. With pollen altered by stress, the fertilization process may be stopped at different stages of its completion. We bring evidence that Cucurbita pepo plants have developed special adaptations in order to compensate for the poor viability of their pollen.Abbreviation FCR fluorochromatic reaction     

Voltage dependence of Na/K pump current inXenopus oocytes

Summary Stage V and VI (Dumont, J.N., 1972.J. Morphol. 136:153–180) oocytes ofXenopus laevis were treated with collagenase to remove follicular cells and were placed in K-free solution for 2 to 4 days to elevate internal [Na]. Na/K pump activity was studied by restoring the eggs to normal 3mm K Barth's solution and measuring membrane current-voltage (I–V) relationships before and after the addition of 10 m dihydroouabain (DHO) using a two-microelectrode voltage clamp. Two pulse protocols were used to measure membraneI–V relationships, both allowing membrane currents to be determined twice at each of a series of membrane potentials: (i) a down-up-down sequence of 5 mV, 1-sec stair steps and (ii) a similar sequence of 1-sec voltage pulses but with consecutive pulses separated by 4-sec recovery periods at the holding potential (–40 mV). The resulting membraneI–V relationships determined both before and during exposure to DHO showed significant hysteresis between the first and second current measurements at each voltage. DHO difference curves also usually showed hysteresis indicating that DHO caused a change in a component of current that varied with time. Since, by definition, the steady-state Na/K pumpI–V relationship must be free of hysteresis, the presence of hysteresis in DHO differenceI–V curves can be used as a criterion for excluding such data from consideration as a valid measure of the Na/K pumpI–V relationship. DHO differenceI–V relationships that did not show hysteresis were sigmoid functions of membrane potential when measured in normal (90mm) external Na solution. The Na/K pump current magnitude saturated near 0 mV at a value of 1.0–1.5 A cm^–2, without evidence of negative slope conductance for potentials up to +55 mV. The Na/K pump current magnitude in Na-free external solution was approximately voltage independent. Since these forward-going Na/K pumpI–V relationships do not show a region of negative slope over the voltage range –110 to +55 mV, it is not necessary to postulate the existence of more than one voltage-dependent step in the reaction cycle of the forward-going Na/K pump.     

Behavior of sperm nuclei in intact and bisected metaphase II mouse oocytes fertilized in the presence of colcemid

Our objective was to examine the developmental fate of sperm nuclei in oocytes fertilized under conditions of meiotic arrest. Therefore zona-free metaphase II oocytes and oocyte fragments (nucleate and anucleate) were fertilized in the presence of colcemid. In anucleate oocyte fragments, normal male pronuclei develop. In contrast, in intact oocytes and nucleate fragments sperm nuclei after initial decondensation undergo secondary condensation. This state is maintained as long as the oocytes are treated with colcemid. When the drug is removed 3 h after insemination, the meiotic spindle(s) is reconstructed, the second polar body(ies) is extruded, and a female pronucleus (or micronuclei) forms. At the same time the sperm nucleus decondenses again and transforms into a male pronucleus. In addition oocytes fertilized in the presence of colcemid could not be refertilized. These observations suggest that oocytes and oocyte fragments fertilized in the presence of colcemid undergo activation despite the failure of pronucleus formation. The inhibitory effect of colcemid on the formation of pronuclei is expressed only in the presence of oocyte chromosomes. We suggest that colcemid stabilizes factors responsible for chromosome condensation that are associated with oocyte chromosomes but not factors (whether the same or different) present in the cytoplasm.     

Gonadotropin-induced murine oocyte maturation in vivo is not associated with decreased cyclic adenosine monophosphate in the oocyte-cumulus cell complex

The cyclic adenosine monophosphate (cAMP) content of intact oocyte-cumulus cell complexes at various times after the induction of oocyte maturation in mice in vivo was correlated with the time of commitment by the oocytes to undergo germinal vesicle breakdown (GVB) and metabolic coupling between the oocyte and cumulus cells. Seventy-nine percent of the oocytes either underwent GVB or were committed to do so by 2 h after injection of human chorionic gonadotropin (hCG). This occurred without a decrease in the coupling between cumulus cells and the oocyte and with increasing cAMP levels in the oocyte-cumulus cell complex. Maintenance of threshold levels of cAMP within mammalian oocytes appears essential for the maintenance of meiotic arrest, but data presented here suggest that oocyte maturation in mice is induced by gonadotropins in nonatretic follicles in vivo by some mechanism other than one which decreases the cAMP content of the intact oocyte-cumulus cell complex.     

Effect of defolliculation and 17α-hydroxy, 20β-dihydroprogesterone on cyclic AMP level in full-grown oocytes of the rainbow trout,Salmo gairdneri

The changes in cAMP were followed in trout oocytes incubated in vitro after defolliculation performed by either enzymatic or manual dissection. Both defolliculation methods induced a highly significant rise in oocyte cAMP level (4.5 times the basal level of control [follicle-enclosed oocytes], after 6 h). Treatment of defolliculated oocytes with 17α-hydroxy,20β-dihydroprogesterone (17α,20β-OH-P) (10^?6 M), which induced oocyte maturation (germinal vesicle breakdown [GVBD]) was able, first, to interrupt the increase of oocyte cAMP level promoted by defolliculation and then to lower this level significantly down to values that still remained higher than folliculated controls. Very low concentrations of 17α,20β-OH-P (1.38–55.6 10^?9 M), or physiological doses of testosterone (0.35 10^?6 M, in the range found in vivo before ovulation) were able to induce a similar decrease of oocyte cAMP level without inducing GVBD. Under the same experimental conditions estradiol (0.35 10^?6 M) exhibited no action. These results suggest that some factor(s) originating in the follicle (FIF), inhibit the oocytes' tendency to accumulate cAMP before the final surge of 17α,20β-OH-P. This factor might be a follicular steroid such as testosterone or nonmaturing concentrations of 17α,20β-OH-P. Moreover our data favour the hypothesis that the final surge of 17α,20β-OH-P could induce distinct intraoocyte mechanisms: the first induces an irreversible blockage of cAMP level before the inhibitory action of the FIF is suppressed by ovulation, and the second mechanism leads to GVBD.     

Complete reversion of the abo phenotype in D. melanogaster occurs only when the blood transposon is lost from region 32E.

Summary The abnormal oocyte phenotype is characterized by instability, as shown by the loss and reappearance of the abo maternal effect under specific genetic conditions. Our previous finding that a correlation exists between the abo phenotype and the presence of a blood transposon in region 32E, led us to perform an extensive genetic and molecular analysis of the most significant aspects of the abo phenotype in different genetic backgrounds. The results of these experiments can be summarized as follows: Complete reversion occurs only when the blood transposon is lost, thus definitively demonstrating that the insertion of the blood transposon in region 32E is the molecular event that causes the pleiotropic abo phenotype. Partial reversion can also occur without loss of the transposon, indicating that different molecular pathways may be involved in the loss of the abo phenotype. Reappearance of the full abo phenotype can occur only in heterozygous lines constructed from partially revertant abo homozygous lines that have not lost the blood transposon.     

A rat oocyte differentiation antigen (OA-1) detected by a monoclonal antibody

Cell surface antigenic changes associated with differentiation of the rat oocyte and early embryo have been demonstrated with a monoclonal antibody (anti-OA-1). Antigen is first detectable coincident with initiation of oocyte growth, is a constant feature of all growing oocytes and displays a redistribution during meiotic maturation. Following fertilization, antigen is detectable on the surface of the embryo through the four-cell stage. This first monospecific marker for the rat oocyte and embryo should prove useful in probing structure/function relationships in oocyte growth, meiotic maturation fertilization, and/or early embryonic development.