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C Simerly

Publications and source records attributed to C Simerly.

At least 37 records · Page 2Linked to original sources
PubMed1999

Biparental inheritance of gamma-tubulin during human fertilization: molecular reconstitution of functional zygotic centrosomes in inseminated human oocytes and in cell-free extracts nucleated by human sperm.

Human sperm centrosome reconstitution and the parental contributions to the zygotic centrosome are examined in mammalian zygotes and after exposure of spermatozoa to Xenopus laevis cell-free extracts. The presence and inheritance of the conserved centrosomal constituents gamma-tubulin, centrin, and MPM-2 (which detects phosphorylated epitopes) are traced, as is the sperm microtubule-nucleating capability on reconstituted centrosomes. gamma-Tubulin is biparentally inherited in humans (maternal >> than paternal): Western blots detect the presence of paternal gamma-tubulin. Recruitment of maternal gamma-tubulin to the sperm centrosome occurs after sperm incorporation in vivo or exposure to cell-free extract, especially after sperm "priming" induced by disulfide bond reduction. Centrin is found in the proximal sperm centrosomal region, demonstrates expected calcium sensitivity, but appears absent from the zygotic centrosome after sperm incorporation or exposure to extracts. Sperm centrosome phosphorylation is detected after exposure of primed sperm to egg extracts as well as during the early stages of sperm incorporation after fertilization. Finally, centrosome reconstitution in cell-free extracts permits sperm aster microtubule assembly in vitro. Collectively, these results support a model of a blended zygotic centrosome composed of maternal constituents attracted to an introduced paternal template after insemination.

Animals↗
PubMed1998

Differential expression and functions of cortical myosin IIA and IIB isotypes during meiotic maturation, fertilization, and mitosis in mouse oocytes and embryos.

To explore the role of nonmuscle myosin II isoforms during mouse gametogenesis, fertilization, and early development, localization and microinjection studies were performed using monospecific antibodies to myosin IIA and IIB isotypes. Each myosin II antibody recognizes a 205-kDa protein in oocytes, but not mature sperm. Myosin IIA and IIB demonstrate differential expression during meiotic maturation and following fertilization: only the IIA isoform detects metaphase spindles or accumulates in the mitotic cleavage furrow. In the unfertilized oocyte, both myosin isoforms are polarized in the cortex directly overlying the metaphase-arrested second meiotic spindle. Cortical polarization is altered after spindle disassembly with Colcemid: the scattered meiotic chromosomes initiate myosin IIA and microfilament assemble in the vicinity of each chromosome mass. During sperm incorporation, both myosin II isotypes concentrate in the second polar body cleavage furrow and the sperm incorporation cone. In functional experiments, the microinjection of myosin IIA antibody disrupts meiotic maturation to metaphase II arrest, probably through depletion of spindle-associated myosin IIA protein and antibody binding to chromosome surfaces. Conversely, the microinjection of myosin IIB antibody blocks microfilament-directed chromosome scattering in Colcemid-treated mature oocytes, suggesting a role in mediating chromosome-cortical actomyosin interactions. Neither myosin II antibody, alone or coinjected, blocks second polar body formation, in vitro fertilization, or cytokinesis. Finally, microinjection of a nonphosphorylatable 20-kDa regulatory myosin light chain specifically blocks sperm incorporation cone disassembly and impedes cell cycle progression, suggesting that interference with myosin II phosphorylation influences fertilization. Thus, conventional myosins break cortical symmetry in oocytes by participating in eccentric meiotic spindle positioning, sperm incorporation cone dynamics, and cytokinesis. Although murine sperm do not express myosin II, different myosin II isotypes may have distinct roles during early embryonic development.

Animals↗
PubMed1998

Fertilization and embryo development to blastocysts after intracytoplasmic sperm injection in the rhesus monkey.

Notwithstanding the thousands of seemingly healthy children born after intracytoplasmic sperm injection (ICSI), it is not yet possible to conclude absolutely that the ICSI procedure might induce some altered development or that the ICSI protocol might not be improved even further. To address this in a clinically relevant system, the developmental potential of rhesus monkey embryos produced by ICSI is reported. Oocytes collected by laparoscopy from gonadotrophin-stimulated fertile females were fertilized by ICSI using spermatozoa obtained from fertile males by electro-ejaculation. Neither sperm immobilization prior to injection nor an additional chemical stimulus were necessary to achieve oocyte activation and pronuclear formation. Survival and activation of the injected oocytes were judged by the extrusion of the second polar body. Successful fertilization was confirmed by the presence of two pronuclei within 12 h post-ICSI. Some oocytes were fixed and processed for the detection of microtubules and chromatin. Fluorescent labelling revealed that by 12 h post-ICSI the male and female pronuclei were closely apposed and eccentrically positioned within a large microtubule aster. ICSI resulted in a 76.6 +/- 14.9% fertilization rate. First cleavage was completed within 24 h post-ICSI. Two-cell ICSI embryos were co-cultured in CMRL medium on a buffalo rat liver cell monolayer until the hatched blastocyst stage. Oocytes collected laparoscopically from stimulated monkeys can be fertilized by ICSI and will complete preimplantation embryo development in vitro demonstrating that the rhesus monkey is an excellent preclinical model for examining and understanding many aspects of human ICSI.

Animals↗
PubMed1998

Assembly of nuclear pore complexes and annulate lamellae promotes normal pronuclear development in fertilized mammalian oocytes.

In addition to functional nuclear pore complexes engaged in nucleo-cytoplasmic transport, the cytoplasmic stacks of pore complexes, called annulate lamellae, exist in numerous cell types. Although both annulate lamellae and nuclear pore complexes are present in fertilized mammalian oocytes, their relative roles in the process of fertilization and preimplantation development are not known. Using epifluorescence and electron microscopy, we explored their fate during bovine fertilization. The assembly of annulate lamellae in bovine oocytes was triggered by sperm-oocyte binding and continued concomitantly with the incorporation of the nuclear pores in the nuclear envelopes of the developing male and female pronuclei. This process was also induced by the parthenogenetic activation of metaphase-II-arrested oocytes. Depletion of Ca2+, previously implicated in oocyte activation and in the insertion of pore complexes into the nuclear envelope, prevented the formation of nuclear pore complexes, but not the assembly of annulate lamellae in oocyte cytoplasm. Injection of the nuclear pore antagonist, wheat germ agglutinin, into the cytoplasm of mature oocytes that were subsequently fertilized caused the arrest of pronuclear development, indicating the requirement of nuclear pore complexes for normal pronuclear development. Treatment of the fertilized oocytes with the microtubule inhibitor, nocodazole, prevented gathering of annulate lamellae around the developing pronuclei, insertion of nuclear pores into their nuclear envelopes, and further pronuclear development. The formation of the male pronuclei was reconstituted in Xenopus egg extracts and reflected the behavior of nuclear pores during natural fertilization. These data suggest that nuclear pore complexes are required for normal pronuclear development from its beginning up until pronuclear apposition. Annulate lamellae may be involved in the turnover of nuclear pore complexes during fertilization, which is in turn facilitated by the reorganization of oocyte microtubules and influx of Ca2+ into oocyte cytoplasm.

Animals↗
PubMed1997

Evidence for the presence of myosin I in the nucleus.

We produced and affinity-purified polyclonal antibodies to adrenal myosin I. These antibodies recognize adrenal myosin I by Western blot analysis (116 kDa) and inhibit the actin-activated ATPase activity of purified adrenal myosin I. They also recognize a 120-kDa protein in extracts prepared from many different cell lines. Fluorescence microscopy demonstrated the presence of immunoreactive material in the perinuclear region, the leading edges, and the nuclei of 3T3 cells. Fluorescence microscopy also demonstrated nuclear staining in mouse oocytes at the germinal vesicle stage and in the pronuclei during fertilization. Confocal and immunoelectron microscopy confirmed the intranuclear localization. Electron microscopy also demonstrated staining of structures in nucleoli that are thought to be associated with rDNA transcription. Western blot analyses revealed the presence of the 120-kDa protein in extracts prepared from nuclei that are apparently free of cytosolic contamination. The same nuclear protein binds 125I-calmodulin and is photoaffinity labeled with [alpha-32P]ATP. The 120-kDa protein was partially purified from twice washed nuclei using ammonium sulfate fractionation and gel filtration chromatography. Column fractions containing 120-kDa protein as revealed by Western blot analysis also contain K+-EDTA ATPase activity. The 120-kDa protein was also shown to bind actin in the absence, but not the presence, of ATP. Since K+-EDTA ATPase activity, actin, and ATP binding are defining features of the members of the myosin superfamily of proteins, we propose that the 120-kDa protein is a previously undescribed myosin I isoform that is an intranuclear actin-based molecular motor.

3T3 Cells↗
PubMed1997

Microtubule organization and chromatin configurations in hamster oocytes during fertilization and parthenogenetic activation, and after insemination with human sperm.

The cytoskeletal components of hamster oocytes, zygotes, and spontaneously activated parthogenotes were examined after immunocytochemical labeling. Microtubules were found only in the anastral, tangentially arranged second meiotic spindle of unfertilized oocytes. Taxol treatment of unfertilized oocytes greatly augmented astral microtubules in both the metaphase II spindle and the cortex. Disruption of the meiotic spindle microtubules with nocodazole resulted in cortical chromosomal scattering. During hamster sperm incorporation and pronuclear formation, no sperm aster was detected in association with the male DNA. Instead, a large overlapping array of microtubules assembled in the cortex. By mitosis, this interphase array disassembled and an anastral metaphase spindle formed. Microtubule and chromatin configurations were also imaged in hamster oocytes injected with human sperm. Astral microtubules were absent from the sperm centrosome. The implications of these results are discussed in relation to the hamster oocyte penetration assay, a test commonly used by in vitro fertilization clinics to demonstrate the fertilizing ability of human sperm. We conclude that since hamsters and humans follow different methods of centrosome inheritance, maternal and paternal, respectively, the hamster may be an inappropriate model for exploring microtubule and centrosomal defects in humans or for assaying postinsemination forms of human male fertility defects.

Animals↗
PubMed1997

A casein kinase I isoform is required for proper cell cycle progression in the fertilized mouse oocyte.

Casein kinase I is a family of serine/threonine protein kinases common to all eukaryotes. In yeast, casein kinase I homologues have been linked to the regulation of growth, DNA repair and cell division. In addition, their subcellular localization to membraneous structures and the nucleus is essential for function. In higher eukaryotes, there exist seven genetically distinct isoforms: (alpha), ss, (gamma)1, (gamma)2, (gamma)3, (delta) and (epsilon). Casein kinase I(alpha) exhibits a cell cycle-dependent subcellular localization including an association with cytosolic vesicular structures and the nucleus during interphase, and the spindle during mitosis. casein kinase I has also been shown to modulate critical regulators of growth and DNA synthesis/repair in mammalian cells such as SV40 large T antigen and p53. These results suggest that casein kinase I may be involved in processes similar to those ascribed to the yeast casein kinase I homologues. To define a role for casein kinase I(alpha) in cell cycle regulation, the mouse oocyte was utilized because of its well-defined cell cycle and ease of micromanipulation. Immunofluorescence studies from meiosis I of maturation to the first zygotic cleavage demonstrated that the kinase was associated with structures similar to those previously reported. Microinjection of casein kinase I(alpha) antibodies at metaphase II-arrest and G2 phase, had no effect on the completion of second meiosis or first division. However, microinjection of these antibodies during the early pronucleate phase prior to S-phase onset blocked uptake of the kinase into pronuclei and interfered with proper and timely cell cycle progression to first cleavage. These results suggest that the kinase regulates the progression from interphase to mitosis during the first cell cycle.

Animals↗
PubMed1997

Inheritance defects of the sperm centrosome in humans and its possible role in male infertility.

During fertilization in humans, the sperm introduces the centrosome, the oocyte's microtubule organizing centre (MTOC), restoring centrosome function. The newly activated oocyte initiates extrusion of the second polar body and begins pronuclear formation. Apposition of the male and female pronuclei requires microtubule-mediated motility in the form of an aster of microtubules emanating from the sperm centrosome. The centrosome then duplicates and separates, forming the two poles of the mitotic spindle, upon which the parental genomes intermix, completing fertilization. The restoration and function of the centrosome is critical for successful fertilization suggesting that a defective sperm centrosome will lead to fertilization arrest and may be a new cause of male infertility. Several types of fertilization failure, associated with the sperm centrosome, are documented. These include: i) failure of the sperm to nucleate microtubules after sperm incorporation; ii) detachment of the sperm centrosome from the sperm head; and iii) failure in microtubule elongation after successful sperm aster formation. Although some types of severe male infertility can be overcome with the use of intracytoplasmic sperm injection (ICSI), men with defective sperm centrosomes are unlikely to benefit. The rate of sperm aster formation, size and organization during bovine fertilization has been used as a measurement of bovine sperm quality. Sperm from bulls which developed large highly organized sperm asters resulted in a higher rate of fertilization in vitro. The development of an assay using Xenopus laevis oocyte extracts has also been used to test centrosome function and sperm aster formation using sperm from men with questionable fertility. In general, these sperm were incapable of forming sperm asters and when used for in vitro fertilization, resulted typically in fertilization failure. These discoveries on the inheritance and function of the sperm centrosome have revealed a new cause of fertilization failure linked to male infertility which may not be circumvented using ICSI.

Animals↗
PubMed1996

Microtubule organization in porcine oocytes during fertilization and parthenogenesis.

Microtubule configurations in porcine oocytes after sperm penetration or after artificial activation by electrical stimulation were imaged by immunocytochemistry and laser scanning confocal microscopy. Soon after sperm penetration, an aster was seen adjacent to the incorporated sperm head. Polyspermic penetrations led to the presence of multiple sperm asters in association with each sperm. The sperm aster enlarged and, at the time of pronuclear apposition, filled the cytoplasm. After male and female gamete union, the microtubule matrix was reduced. At the mitotic metaphase stage, microtubules were detected in the spindle, which was anastral and fusiform. At anaphase, asters assembled at each spindle pole, and at telophase, large asters filled the cytoplasm. Artificial activation by electrical stimulation induced in the cytoplasm a dense network of microtubules, which seem to be involved in proper positioning of the female pronucleus. At mitotic metaphase, microtubules were concentrated around the chromatin. The results of experiments using taxol, a microtubule stabilizing agent, suggest that maternal centrosomal material is present in the mature porcine oocyte as dispersed undetectable material that can form a microtubule network after parthenogenetic activation. However, at fertilization, the paternal centrosome collects centrosomal material to form a sperm aster. These results suggest that the functional centrosome that forms during fertilization is a result of the blending of paternal and maternal centrosomal components.

Animals↗
PubMed1996

Microtubule and chromatin dynamics during fertilization and early development in rhesus monkeys, and regulation by intracellular calcium ions.

To explore primate fertilization, oocytes and zygotes from fertile rhesus monkeys were imaged throughout fertilization, polyspermy, and artificial activation using confocal microscopy for microtubules and DNA, as well as ratiometric computer-enhanced video microscopy for intracellular calcium. Unfertilized oocytes displayed microtubules only in the radially oriented meiotic spindles. At insemination, a large calcium transient was followed by a series of smaller oscillations, and sperm astral microtubules had assembled from the sperm centrosome by 2.5 h after transient onset. This aster enlarged, and later duplicated, as the pronuclei converged near the cortex. Pronuclear apposition was prevented by microtubule inhibitors. At mitotic prophase, microtubules ensheathed both sets of condensing chromosomes. At metaphase, the spindle was barrel-shaped and eccentrically positioned with two small asters at the pole with the sperm tail. Microtubules emanating from the telophase spindle interacted with the adjacent cortex and displaced the spindle toward the cell center as first cytokinesis ensued. During polyspermy, each sperm nucleated an aster, and the frequency of calcium oscillations increased. Activation resulted initially in disarrayed microtubules that eventually organized into functional mitotic spindles. These kinetic results demonstrate that rhesus monkeys accomplish fertilization in a fashion nearly identical to that of humans and are, therefore, ideal models in which to investigate cytoskeletal events during human reproduction.

Adenine↗
PubMed1996

Molecular medical approaches for alleviating infertility and understanding assisted reproductive technologies.

Fertilization is a precisely orchestrated cascade of events that results in the union of paternal and maternal genomes and in the establishment of mitotic potential of the zygote. To initiate embryonic development, the structures of the fertilizing sperm have to be disassembled and transformed into zygotic components by interactions with the cytoplasm of the egg. These interactions include the decondensation of the sperm nucleus into male pronucleus, the assembly of the zygotic centrosome, and the gathering of centrosomal proteins and sperm aster microtubules around the sperm centriole. Both the formation of the male pronucleus and the assembly of the zygotic centrosome are crucial steps required for pronuclear apposition and genomic union. The discovery of previously undetected fertilization failures that are due to defects in the assembly of the zygotic centrosome, abnormal pronuclear development, and compromised cytoskeletal dynamics enforces the development of new diagnostic strategies. Moreover, the introduction of new methods of infertility treatments, such as intracytoplasmic sperm injection and round spermatid nucleus injection into assisted human reproductive technology programs, emphasizes our lack of understanding of the cellular and molecular basis of human fertilization and evokes the need for additional experimentation. These efforts, however, are compromised by the sensitive nature of human embryo research and thus are severely restricted. Animal models that are reliable and cost-effective and that feature the characteristics of human fertilization have therefore been sought. Rodents such as the rat, mouse, and hamster are poor models owing to their maternal inheritance of the zygotic centrosome that is in strong contrast with the biparentally contributed assembly of the human zygotic centrosome during fertilization. Although rabbits are similar to humans from the standpoint of mitotic potential inheritance, information on postfertilization events in rabbits are lacking. Nonhuman primates represented by the rhesus monkey proved to be a reliable model for human in vitro fertilization and intracytoplasmic sperm injection, an advantage that is further emphasized by phyllogenetic similarity. In situations in which the high cost of primate research does not allow for large-scale experimentation (i.e., when large numbers of oocytes and embryos are needed), ruminants would be an ideal solution. Represented by the cow and sheep, domestic ruminants feature a fertilization strategy similar to that of the human. In addition, large numbers of gametes can be obtained wherever farms and slaughterhouses are accessible. Moreover, the detailed information on ruminant fertilization is strengthened by years of research and well-defined reproductive technology aimed at increasing the productivity of farm animals. Ruminants and rhesus monkeys have been extensively studied, and the data from these studies have been extrapolated in order to propose new strategies for the diagnosis and treatment of human infertility.

Animals↗
PubMed1995

Imaging motility during fertilization.

Studying reproduction in domestic species is now possible at the cellular and molecular level due to advances in the production of large numbers of zygotes and embryos in these species. In this paper we review the microtubule patterns during fertilization in domestic species. These results indicate that domestic species accomplish fertilization in a similar fashion to one another but in a far different fashion from rodents. Recent results indicate that human fertilization is similar to that of domestic species. We discuss the significance this has on the use of domestic species as a model system for human studies and possible consequences for the alleviation of human infertility.

Animals↗
PubMed1995

The paternal inheritance of the centrosome, the cell's microtubule-organizing center, in humans, and the implications for infertility.

Successful fertilization in humans, achieved when parental chromosomes intermix at first mitosis, requires centrosome restoration and microtubule-mediated motility. Imaging of inseminated human oocytes reveals that the sperm introduces the centrosome. The centrosome then nucleates the new microtubule assembly to form the sperm aster--a step essential for successful fertilization. Oocytes from some infertile patients failed to complete fertilization because of defects in uniting the sperm and egg nuclei, indicating that failure to properly effect the cytoplasmic motions uniting the nuclei results in human infertility. These discoveries have important implications for infertility diagnosis and managing reproduction.

Centrosome↗
PubMed1995

The sperm centrosome during fertilization in mammals: implications for fertility and reproduction.

This article reviews the recent discoveries that: (1) nearly all mammals, including humans, inherit their centrosomes from their fathers; and (2) some sperm are ineffective in organizing the microtubules essential for effecting genomic union during fertilization, leading to the speculation that these sperm have centrosome defects. In addition, the molecular dissection and reconstitution of the human sperm centrosome in vitro is presented.

Animals↗
PubMed1995

The stages at which human fertilization arrests: microtubule and chromosome configurations in inseminated oocytes which failed to complete fertilization and development in humans.

The goal of fertilization is the union of one, and only one, sperm nucleus with the female pronucleus within the activated oocyte. For this to occur successfully, several events must transpire, including the incorporation of the entire spermatozoon into the oocyte, the completion of meiotic maturation with the extrusion of the second polar body, the metabolic activation of the previously quiescent oocyte, the decondensation of the sperm nucleus and the maternal chromosomes into the male and female pronuclei respectively, and the cytoplasmic migrations of the pronuclei, which bring them into apposition. Defects in any of these events are lethal to the zygote and might prove to be causes of infertility. In this study, the microtubules and DNA were imaged in inseminated human oocytes that had been discarded as unfertilized. The presence and number of incorporated sperm tails were also documented using a monoclonal antibody specific for the post-translationally modified acetylated-alpha-tubulin found in the tail, but not the oocyte, microtubules. An analysis of 211 oocytes from failed in-vitro fertilizations from 58 patient couples resulted in the determination of several previously undetectable phases at which fertilization arrests: (i) metaphase II arrest; (ii) arrest after the successful incorporation of the spermatozoon, (iii) arrest after the formation of the sperm aster; (iv) arrest during mitotic cell cycle progression; and (v) arrest during meiotic cell cycle progression. Data on polyspermy and arrested embryonic development are also presented. These results have implications for the diagnosis and treatment of female, as well as male, infertility.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Cycle↗
PubMed1994

Microtubule configurations in oocytes, zygotes, and early embryos of a marsupial, Monodelphis domestica.

The marsupials represent a separate evolutionary lineage from eutherians from which they diverged over 100 million years ago. In order to explore the origin and mode of centrosome inheritance amongst this group of mammals, this study investigates the microtubule organization during fertilization, parthenogenesis, and polyspermy in the didelphid, Monodelphis domestica. Microtubules and DNA were visualized in maturing ovarian oocytes, parthenogenetically activated oocytes, monospermic and polyspermic zygotes, and early embryos. Ovarian oocytes had a central region of yolky cytoplasm that, after fertilization, became polarized; much of the yolk was then extruded into the perivitelline space as an enucleated cytoplasmic mass. Immunofluorescence microscopy, using a monoclonal antibody to beta-tubulin, demonstrated microtubules in the meiotic spindle in unfertilized oocytes, but cytasters were not detected. After fertilization, a cluster of microtubules forming into a sperm aster was evident around the male pronucleus. The sperm aster remained largely restricted to the nonyolky region of the egg cytoplasm, resulting in a cytoplasmic heterogeneity between a microtubule-rich region and one in which microtubules were largely absent. Once the two pronuclei came close together, abundant microtubules were found surrounding both pronuclei. In the early embryo, microtubules were found in the outer cortical region of the blastomeres and, in addition, there was an extensive and elaborate network of microtubules throughout the yolk mass. Disruption of the meiotic spindle microtubules with nocodazole or cold treatment did not result in chromosome dispersion in the cortex and recovery from drug or cold depolymerization demonstrated that microtubules might not be as dynamic as those in eutherian mammals. Taxol stabilization resulted in an increase in cortical microtubules. In this marsupial species, therefore, the centrosome appears to be of paternal origin, and the radiating microtubules that form may well be involved both in bringing the pronuclei together and in the cytoplasmic polarization that results in extrusion of the yolk mass.

Animals↗