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J Van Blerkom

Publications and source records attributed to J Van Blerkom.

At least 19 recordsLinked to original sources
PubMed1992

Oocyte dysmorphism and aneuploidy in meiotically mature human oocytes after ovarian stimulation.

The frequency of aneuploidy in 583 newly aspirated, uninseminated metaphase II-stage human oocytes which exhibited seven distinct forms of cytoplasmic dysmorphism [Van Blerkom (1990) J. Electron Microsc. Tech., 16,324] after ovarian stimulation and ovulation induction was determined in the living state by DNA fluorescence followed by fixation and air-drying for karyotyping. The findings demonstrate that as many as half of the oocytes with dysmorphic phenotypes which arise early in meiotic maturation are aneuploid, with hypohaplidy predominant. In contrast, cytoplasmic defects which occur at or after metaphase I are associated with a relatively low frequency of aneuploidy (less than 15%), which is comparable to that previously reported for human oocytes with a normal cytoplasmic appearance [Van Blerkom and Henry (1988) Hum. Reprod., 3, 777]. The aetiologies of aneuploidy in dysmorphic oocytes, as well as the clinical implications for oocyte selection in laboratory-assisted conception are discussed.

Adult↗
PubMed1991

Microtubule mediation of cytoplasmic and nuclear maturation during the early stages of resumed meiosis in cultured mouse oocytes.

A perinuclear accumulation of mitochondria characterizes the premetaphase I stages of reinitiated meiosis in the laboratory mouse oocyte. The cellular basis of this organelle-specific translocation was examined by fluorescent probe analysis, immunostaining, and immunoelectron microscopy in oocytes cultured at specific stages of meiotic maturation in the presence and absence of drugs that influence the stability of microfilaments and microtubules. The results suggest that a temporal, spatial, and developmental relationship exists between the location of microtubule organizing centers and the progressive translocation of mitochondria to the nuclear region. The findings indicate that mitochondrial translocations are mediated by microtubules and that individual microtubule organizing centers are not only foci for mitochondrial aggregation but may also facilitate the establishment of the circular bivalent configuration.

Animals↗
PubMed1991

Dispermic fertilization of human oocytes.

Regardless of whether fertilization occurs in vivo or in vitro, polyspermic penetration of the human oocyte is a not infrequent cause of reproductive failure. This report describes the occurrence of human eggs fertilized by two spermatozoa and the variable developmental potentials expressed by the resultant embryos. The cellular and subcellular events that characterize the pronuclear and early cleavage stages of preimplantation embryogenesis are discussed with respect to the ability of such embryos to progress to implantation.

Aneuploidy↗
PubMed1990

Cellular and developmental biological aspects of bovine meiotic maturation, fertilization, and preimplantation embryogenesis in vitro.

Cellular aspects of reinitiated meiosis, fertilization, and early preimplantation embryogenesis in the bovine species were examined under in vitro conditions. An analysis of the cytoplasmic distribution of mitochondria, lipid droplets and vesicles in over 5,000 living GV-stage oocytes, with subsequent examination by electron microscopy, indicated that the organization of cytoplasm was pleomorphic and that five distinct cellular phenotypes could be identified. Inspection of oocytes during the resumption of arrested meiosis in vivo and in vitro demonstrated that the subcellular organization of the bovine oocyte cytoplasm remains unchanged during maturation to metaphase II. The influence of culture conditions and media on the frequency of maturation, cytoplasmic organization, fertilizability, and early preimplantation embryogenesis was also determined. The findings indicate that meiotic maturation and fertilization in the bovine species can occur at high frequency under comparatively simple and defined conditions. However, the acquisition of developmental competence for fertilization, and the ability of the egg to develop progressively after fertilization appears to be related to the organization of the cytoplasm at the GV stage. The relationship between cytoplasmic organization and conditions of maturation, fertilization, presence or absence of cumulus cells, and the acquisition of developmental competence is discussed with respect to 1) cell biological aspects of mammalian oocyte maturation, 2) the potential influence of extrinsic factors (e.g., differential intrafollicular biochemistry and morphophysiology) on subcellular organization of the GV-stage oocyte, and 3) the finding that morphologically equivalent bovine embryos derived from the in vitro fertilization of in vitro-matured oocytes may be developmentally heterogeneous. The studies also revealed that nuclear and cytoplasmic aberrations which could preclude normal embryogenesis can develop shortly after fertilization. The significance of this finding with respect to cytoplasmic phenotype of the oocyte and conditions of maturation, fertilization, and early embryo culture is discussed.

Animals↗
PubMed1990

Occurrence and developmental consequences of aberrant cellular organization in meiotically mature human oocytes after exogenous ovarian hyperstimulation.

The extent to which fertilization failure in in vitro inseminated human oocytes obtained from hyperstimulated ovaries was associated with alterations in cellular structure and cytoplasmic organization was examined by a combination of DIC, fluorescence, time-lapse video, and transmission electron microscopy. Detailed analysis of meiotically mature preovulatory (uninseminated) oocytes, and of oocytes that failed to fertilize in vitro, indicated that between 10% and 15% of grossly normal-appearing MII-stage oocytes displayed one of the following cellular perturbations: 1) a subtle change in organelle distribution, 2) a small region(s) of intracellular cytolysis, 3) a massive aggregation of SER tubules, 4) an accumulation of vesicles presumed to be of SER origin, 5) a change in the structural organization of the cortical cytoplasm and overlying plasma membrane, 6) a sudden and rapid internalization of perivitelline fluid by means of an apparently aberrant process of endocytosis, and 7) a premature and partial exocytosis of cortical granules. The description of these disorders is discussed with respect to the developmental consequences for the oocyte.

Cell Degranulation↗
PubMed1989

Maturation at high frequency of germinal-vesicle-stage mouse oocytes after cryopreservation: alterations in cytoplasmic, nuclear, nucleolar and chromosomal structure and organization associated with vitrification.

After thawing and culture in vitro, greater than 90% of germinal-vesicle (GV)-stage mouse oocytes cryopreserved by vitrification, were capable of resuming meiosis and undergoing normal chromosomal and cytoplasmic maturation to metaphase II. This high frequency of development occurred against a background of profound alterations in the structure and organization of the cytoplasm, nucleus, nucleolus and chromatin during the dehydration stage of vitrification. Most, but not all, cytoplasmic and nuclear perturbations returned to a normal state during post-thaw culture. However, the results clearly demonstrate that vitrification is associated with chromosomal and cellular disorders that could adversely affect development after fertilization. Irreversible changes of potential developmental significance observed after vitrification at the GV stage include (i) premature chromosomal condensation, (ii) mixing of nucleoplasmic and cytoplasmic components prior to GV breakdown, and (iii) externalization of chromatin fragments into the cytoplasm after reformation of the oocyte nucleus, which shows the potential for the generation of fertilizable oocytes containing deleted segments of DNA.

Animals↗
PubMed1988

Cytogenetic analysis of living human oocytes: cellular basis and developmental consequences of perturbations in chromosomal organization and complement.

Chromosome complement and location were examined by fluorescence microscopy for 225 meiotically mature (metaphase II) human oocytes after staining with DNA-specific probes. Both preovulatory oocytes and oocytes that failed to fertilize in vitro were analysed. After inspection in the living state, oocytes were selected for karyotyping or transmission electron microscopy. The findings demonstrate a high correlation between assessments of chromosome complement in living oocytes and the results from subsequent karyotypes. In addition to numerical aberrations (aneuploidy), the results also demonstrate the ability to detect abnormalities in chromosome structure and distribution. Specifically, this approach identified living oocytes that (1) contained no apparent chromosomes in the ooplasm, (2) contained chromosome not associated with the MII spindle and (3) had weak or no detectable chromosomal fluorescence in the first polar body. The findings demonstrate that approximately 8% of the oocytes were aneuploid (hypohaploid or hyperhaploid). Another 6.5% displayed anomalies in chromosome structure or distribution that could lead to aneuploid situations. The results are discussed with respect to the origin, occurrence and developmental consequences for such oocytes.

Adult↗
PubMed1987

The occurrence, recognition and developmental fate of pseudo-multipronuclear eggs after in-vitro fertilization of human oocytes.

The presence of three or more presumed pronuclei in 27 of 884 (3%) in-vitro fertilized human eggs suggested the occurrence of polyspermic fertilization. Detailed examination by differential interference contrast microscopy indicated that approximately 40% of presumed multipronuclear eggs were normally fertilized but contained a cytoplasmic vacuole(s) (pseudo-pronucleus) of pronuclear dimension and gross morphology. Closely timed observations of presumed multipronuclear eggs revealed that pseudo-pronuclei (PPN) can co-migrate and become juxtaposed with true pronuclei, thus presenting the impression of an aberrant fertilization. Fluorescent probe and electron microscopic analyses demonstrated that PPN are enclosed by a plasma membrane and contain neither DNA nor nucleoli. PPN can develop either in the mature oocyte or the newly fertilized egg. Pseudo-multipronuclear eggs progress through the preimplantation stages in an apparently normal fashion and, as demonstrated by one birth and two ongoing pregnancies, are developmentally viable. Criteria for the unambiguous designation of pseudo-multipronuclear eggs are based on: the absence of normal morphodynamic changes associated with pronuclear development; and the failure of nucleoli to appear during the perisyngamic stage. The findings strongly suggest that pseudo-multipronuclear human eggs may represent a class of morphological variants of normally fertilized and developmentally competent eggs.

Cell Nucleolus↗
PubMed1986

Regulation of development in the fully grown mouse oocyte: chromosome-mediated temporal and spatial differentiation of the cytoplasm and plasma membrane.

The relationship between nuclear maturation and the differentiation of the cytoplasm and plasma membrane during resumption of arrested meiosis was investigated by culture of GV-and MII-stage mouse oocytes in the presence and absence of nocodazole. Culture in the presence of nocodazole was associated with dispersal of MI and MII chromosomes throughout the subplasmalemmal cytoplasm. A progression of cortical (thickening of actin filaments) and plasma membrane changes (denudation of microvilli, reduction in cell surface glycoproteins, formation of chromosome-containing evaginations) that normally occurs in proximity to chromosomes associated with intact MI or MII spindles took place only in those regions of the cortical cytoplasm containing the dispersed subplasmalemmal chromosomes. The dispersion and migration of the chromosomes occurred in an apparently random fashion. Fluorescent probe analysis of normal and treated oocytes indicated a stage-specific association between the spatial distribution of chromosomes and mitochondria. Transfer of individual bivalent chromosomes to untreated oocytes at different stages of maturation and to cytoplasts derived from oocytes anucleated prior to GVB demonstrated the necessity of chromosomes for cytoplasmic and plasma membrane differentiation, and that the capacity of the cytoplasm and plasma membrane to differentiate in response to the presence of a chromosome is acquired prior to GVB.

Animals↗
PubMed1984

Mitochondrial reorganization during resumption of arrested meiosis in the mouse oocyte.

Correlated nuclear and cytoplasmic reorganizations during the 14 hr of reactivated meiosis in vivo and in vitro were examined in the laboratory mouse. Observations of living oocytes by differential interference contrast microscopy, and by fluorescent microscopy with nontoxic mitochondrial and DNA-specific probes, enabled us to determine that the major cytoplasmic reorganization involved two mitochondrial translocations associated with two stages of nuclear maturation. These observations were confirmed at the fine structural level by parallel transmission electron microscopy. Mitochondria translocate to the perinuclear region during formation of the first metaphase spindle and subsequently disperse during abstriction of the first polar body. Determinations of frequency of maturation in more than 2,900 normal oocytes, and in more than 1,100 oocytes in which germinal vesicle breakdown was reversibly inhibited, indicated that mitochondrial redistributions are a normal and probably necessary feature of reactivated meiosis in the laboratory mouse. We suggest that these two rapid translocations serve to concentrate mitochondria for localized activities that require elevated levels of adenosine triphosphate.

Animals↗
PubMed1984

Identification and characterization of glycoproteins secreted by the skin of the day 16 fetal mouse.

The secretion of tissue-specific proteins during mouse skin development, was investigated by incubating day 16 fetal skin explants in the presence of [35S]methionine and analyzing the medium electrophoretically. The medium was found to contain five proteins, which could be classified into two groups according to molecular weight. The kinetics of release of these proteins indicated that they were specifically secreted and not released by cytolysis. Mapping of the proteins by partial proteolytic digestion revealed that although the digestion patterns between the two molecular weight groups were different, within each group similar patterns were seen, suggesting that they were structurally related. Incubation in the presence of tunicamycin resulted in the decrease in molecular weight of the secreted proteins, indicating that the proteins were glycosylated. The results suggest that the two groups of structurally related glycoproteins were secreted by the peridermal layer of the fetal skin.

Animals↗
PubMed1984

Human in vitro fertilization in a private program: Reproductive Genetics in Vitro, P.C.

Reproductive Genetics in Vitro, P.C., began a program of human in vitro fertilization in a private practice setting in September of 1982, after nearly 1 year of preparation prior to the cycling of the first patient. Ovarian stimulation is most often by Clomid, 50 mg tid, on days 3 through 9 of the cycle. Follicle development is monitored by daily ultrasound, estradiol, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) measurements. Serum progesterone measurements are made the last few days prior to anticipated ovulation to detect early signs of luteinization. In the first phase of our program 12 patients with pure tubal obstruction have had one or more oocytes retrieved by laparoscopy. All oocytes fertilized such that every patient who had oocytes retrieved had embryos placed in the uterus. Of the first 12 patients who had embryo placement, 2 are ongoing and normal in the second trimester of pregnancy, with delivery expected shortly after the first issue of this journal. Five others showed early signs of clinical pregnancy as indicated by acentrically located gestational sacs (as opposed to the typical centrally located pseudogestational sac) or transiently elevated human chorionic gonadotropin (HCG).

Adult↗
PubMed1984

Preimplantation human embryonic development from polypronuclear eggs after in vitro fertilization.

The occurrence of grossly normal-appearing morula stage human embryos (8- to 12-cell) that developed from eggs fertilized in vitro containing three pronuclei is described. Serial section analysis by transmission electron microscopy demonstrated that 25% of the blastomeres were multinucleate, with as many as five deoxyribonucleic acid-containing nuclei (determined by fluorescence microscopy) in a single cell. Light and electron microscopy indicated that normal cortical and zona reactions had taken place. Fine-structural development of the cytoplasm was characteristic of morula stage human embryos. The results suggest the need to determine pronuclear number prior to syngamy and are discussed with respect to the notion that human embryos may have the capacity to develop normally in spite of the presence of abnormal cells.

Blastomeres↗
PubMed1982

The patterns of protein synthesis during foetal and neonatal organ development in the mouse are remarkably similar.

The extent to which differential gene expressions can be correlated with organ development was examined at the level of protein synthesis during pre- and postnatal development in the mouse. High resolution, equilibrium, two-dimensional polyacrylamide gel electrophoresis detected, for each of five to ten successive stages for each of seven organ systems, between 850 and 1000 separate newly synthesized proteins. The possibility that the 1000 detectable proteins synthesized at any one time during organ development represent a sampling bias was contra-indicated (a) because a different and larger population of [14C]amino acid-incorporating protein syntheses gave similar results and (b) because nonequilibrium isoelectric focusing, electrophoresis, isoelectric points between pH 5.5 and 8.7 confirmed the results from yet a different population of protein syntheses. Within limits of the sampling of protein syntheses, the entire period of organ development examined proceeds with altered expression of small proportion of the total proteins being synthesized. While all protein changes were stage specific, approximately three organ-specific protein syntheses were detected per organ system. One family of five protein syntheses seen in 16-day foetuses had homologous primary structures and presumably are keratins derived from a single genomic expression. These selected stage-specific protein syntheses examined by electrophoresis of partial proteolytic digests disclosed a programme for post-translational changes in protein syntheses. The current observations indicate that the examined pre- and postnatal organ development of the seven organs occurs in the presence of greater than 99% similarity among proteins synthesized in the same and different organ systems. Functional differentiation during organogenesis, therefore, occurs in the presence of less than 1% change in qualitative or quantitative switch in protein syntheses. Evidence is presented to indicate that even this remarkably small number of changes in protein syntheses during functional organ differentiation may be derived from an even smaller subset of gene expressions. Collectively, the data suggest that explanatory mechanisms for molecular organogenesis must encompass both selective gene expressions along with post-translational programmed events.

Amino Acids↗