PubMed Health⌕ Search

Biomedical subjects

N L First

Publications and source records attributed to N L First.

At least 91 records · Page 5Linked to original sources
PubMed1988

Chimerization of highly asynchronous murine blastomeres: developmental alteration?

Previous studies have shown that early embryos contain information that can alter the developmental fate of adjacent cells and transferred nuclei. In this report we show that a specific combination of cells from early murine embryos, a single blastomere from an eight-cell embryo placed under the zona pellucida with a two-cell embryo, results in a difference in incorporation of 3H-uridine and expression of two protein bands between the chimeric treatment group and the nonchimeric controls, a single blastomere from an eight-cell embryo in a separate zona pellucida and a two-cell embryo. The incorporation of 3H-uridine in the chimeric group and nonchimeric control group was significantly different at 45 hours after chimerization (P less than .02). A stage-specific protein band (52k) on a polyacrylamide gel detected with fluorography was found to be qualitatively different (present more often; P less than .01) and another stage-specific protein band (48k) was found to be quantitatively different (more protein; P = .07) in the chimeric treatment vs. the nonchimeric controls at 45 hours after chimerization. These results suggest communication between the cells resulting in a change in their incorporation of uridine and protein synthetic profiles.

Animals↗
PubMed1988

The regulation of acrosomal exocytosis. I. Sperm capacitation is required for the induction of acrosome reactions by the bovine zona pellucida in vitro.

The regulation of acrosomal exocytosis in capacitated bovine spermatozoa by soluble extracts of zonae pellucidae was examined. Kinetic studies demonstrated that zonae pellucidae stimulated synchronous acrosome reactions. The t1/2 of this process was 5-10 min and response was maximal at 20 min. The apparent initial rate of exocytosis in sperm populations was dependent upon the concentration of zona pellucida protein, with an ED50 and a maximally effective dosage of 20 and 50 ng protein/microliter, respectively. Zonae pellucidae caused up to a 48-fold increase in the apparent initial rate and a 3- to 4-fold stimulation in the net occurrence of exocytosis. In contrast, solubilized zonae pellucidae did not induce acrosome reactions in uncapacitated sperm. The development of a capacitated state, as assayed by the ability of sperm to fertilize eggs in vitro, was compared to the expression of zona pellucida-regulated acrosome reactions in a series of kinetic experiments. Both activities were manifest with similar kinetics and displayed identical dependencies toward stimulatory and inhibitory agents in vitro. It is concluded that capacitation is an essential prerequisite for the induction of acrosomal exocytosis in bovine sperm by the zona pellucida.

Acrosome↗
PubMed1988

Regulation of acrosomal exocytosis. II. The zona pellucida-induced acrosome reaction of bovine spermatozoa is controlled by extrinsic positive regulatory elements.

The effects of accessory sex gland secretions on the zona pellucida-induced acrosome reaction of bovine spermatozoa were investigated. Soluble extracts of zonae pellucidae initiated exocytosis in ejaculated spermatozoa. This process had an ED50 of 20 ng/microliter zona pellucida protein and saturated at 50 ng/microliter (Florman and First, 1988. Dev. Biol. 128, 453-463). In epididymal sperm this dose-response relationship was shifted toward greater agonist concentrations by at least a factor of 10(3). Reconstitution of high potency agonist response was achieved in vitro by incubation of epididymal sperm with bovine seminal plasma. Reconstitution was dependent on the seminal plasma protein concentration. The ED50 of this process was 62 micrograms protein/10(8) sperm and saturation was observed with 124 micrograms protein/10(8) sperm. Agonist responses in reconstituted epididymal sperm and in ejaculated sperm were indistinguishable with regard to dependence on the zona pellucida protein concentration and the kinetics of induced acrosome reactions. Kinetic studies suggest that reconstitution is due to adsorption of regulatory factors from seminal plasma. In addition to the positive regulatory elements responsible for reconstituting activity, seminal plasma also contains negative regulatory elements which inhibit agonist response. These negative factors are inactivated during sperm capacitation, permitting the expression of positive regulators. Acting together, these regulatory elements could coordinate high affinity agonist response with the availability of eggs in vivo.

Acrosome↗
PubMed1988

Capacitation of bovine sperm by heparin.

Capacitation of bovine sperm was evaluated by determining the ability of sperm to fertilize bovine oocytes in vitro and to undergo an acrosome reaction upon exposure to lysophosphatidylcholine (LC). Incubation of sperm with heparin (10 micrograms/ml) increased the percentage of oocytes fertilized, but this required exposing sperm to heparin for at least 4 h before adding them to oocytes. There was no effect on the percentage of motile or acrosome-reacted sperm after exposure of noncapacitated sperm to 100 micrograms/ml LC for 15 min. When sperm were incubated for 4 h with heparin, exposure to 100 micrograms/ml LC for 15 min had no effect on the percentage of sperm that were motile, but the percentage of acrosome-reacted sperm increased from less than 10% to over 70%. The acrosome reactions (ARs) induced by LC were synchronous, reached maximal levels within 15 min, and differed (p less than 0.001) between sperm incubated under capacitating (with heparin) and noncapacitating conditions (without heparin). The time course required for heparin to capacitate sperm as judged by in vitro fertilization and to render sperm sensitive to LC induction of the AR were found to be similar. The percentage of ARs induced by LC and percentage of oocytes fertilized by sperm were found to be heparin-dose-dependent, with the maximum responses occurring at 5-10 micrograms/ml heparin. The correlation between the mean fertilization and LC-induced AR percentages was 0.997 (p less than 0.01). These studies demonstrate capacitation of bovine sperm by heparin requires at least a 4-h exposure of sperm to heparin and suggest that plasma membrane changes prior to an AR can be detected by exposure of bovine sperm to LC.

Acrosome↗
PubMed1988

In vitro inhibition of oocyte nuclear maturation in the bovine.

Bovine follicular oocytes (N = 5991) were exposed to an analog of cyclic adenosine 3',5'-monophosphate (cAMP), dibutyryl cyclic AMP (db-cAMP) (2.5, 5, and 10 mM), the phosphodiesterase inhibitor isobutyl methyl xanthine (IBMX, 0.2 mM), or the purine, hypoxanthine (0.5, 1.0, 2.0 mM), and the nucleoside, adenosine (0.05, 0.1, 0.2 mM), for 6 or 21 h to assess their effects on oocyte nuclear maturation. Potential effects of bovine follicular fluid (BFF) were also evaluated after different preculture washing procedures. In a separate experiment, denuded oocytes were used to study the effect of cumulus removal on meiotic inhibition. Db-cAMP decreased the frequency of germinal vesicle breakdown (GVBD) at 6 h (88% for control and 51%, 45%, and 32% for 2.5, 5, and 10 mM concentrations, respectively). IBMX had a comparable effect with only 41% of the oocytes resuming meiosis. Hypoxanthine and adenosine alone or in combinations also decreased the number of oocytes undergoing GVBD at 6 h. Only 22% GVBD occurred when the combined highest concentration of both substances was used compared to 88% in controls. If oocytes were incubated in 50% BFF after a wash in control medium during processing, 56% would resume meiosis at 6 h vs. 35% if the washing procedure included inhibitors (db-cAMP + IBMX). Total BFF (100%) during washing and maturation prevented 72% of the oocytes from resuming meiosis. Db-cAMP and IMBX combined or BFF also inhibited meiotic resumption of denuded oocytes. At 21 h, the inhibitory effects were less pronounced, with most oocytes only delayed in completing the first reduction division.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1988

The culture of bovine oocytes to obtain developmentally competent embryos.

Bovine cumulus-oocyte complexes (COC) (n = 4230) were used in this study to assess the effects of culture method, hormonal supplementation, and cumulus cell concentration on maturation, fertilization and development of resulting embryos. Five treatments were evaluated. 1) 10 COC/50-microliter drops under oil in TCM 199 supplemented with 10% heat-treated fetal calf serum, follicle-stimulating hormone (0.5 microgram/ml), luteinizing hormone (5 micrograms/ml), and estradiol-17 beta (1 microgram/ml); 2) as in 1 without hormones; 3) as in 1 but in 3 ml TCM-199 in petri dishes without paraffin oil; 4) as in 2 but only 1 COC/50-microliter drop; and 5) as in 1 but with denuded oocytes. After 24 h maturation, the frequencies of oocytes reaching metaphase II were 98, 84, 92, 93, and 87%, respectively, for the five treatments. In the same order, percentages of normal fertilization were 73, 70, 62, 81, and 62%, and the frequencies of embryos containing two or more blastomeres at 65 h postinsemination were 69, 82, 66, 51, and 43%. The same five treatments were used in a second study in which 3,199 oocytes were fertilized, allowed to cleave in vitro to the 2- to 3-cell stage (42 h postinsemination), and transferred to oviducts of sheep (one treatment/oviduct) for 4 days. The frequencies of morulae or blastocytes obtained were 28, 18, 23, 24, and 11% for the five treatments, respectively. After nonsurgical transfer to bovine recipients (n = 8) using fresh or frozen-thawed embryos, three pregnancies past 50 days were obtained. Only one went to term with the birth of a live heifer calf.

Animals↗
PubMed1988

A review of early mouse embryogenesis and its applications to domestic species.

The early mammalian embryo undergoes a variety of changes as development proceeds from the one-cell to the blastocyst stage. Most of these changes can be related to activity of the genome. In the early embryo the genome is quiescent and does not produce RNA until species-specific cell stages. This activation of the embryonic genome results in changes in distribution of cell surface microvilli and spatial organization of cytoplasmic organelles, as well as in establishment of cellular junctions and differential utilization of carbohydrates as energy sources. Many of these events have been well characterized for the mouse, but similar comparative studies in domestic species are lacking. This review attempts to highlight early development in the mouse and draw comparisons with domestic species.

Animals↗
PubMed1987

Developmental fate in chimeras derived from highly asynchronous murine blastomeres.

The developmental fate of single blastomeres from eight-cell murine embryos reaggregated with intact two-cell embryos was evaluated after culture. Fluorescein isothiocyanate was used to follow developmental fate in preblastocyst chimeric embryos. Expression of stage-specific embryonic antigen 3 was used to assay developmental fate at the blastocyst stage, and glucosephosphate isomerase variants were used to assay at the blastocyst stage and after implantation. The results suggest that the descendents of the 1/8 component stay in a patch area and do not selectively migrate to the inner cell mass (ICM). This is in contrast to many studies that indicate that smaller blastomeres, which are more advanced in development, migrate to the ICM. The differences in experimental designs are discussed. Possible mechanisms for this phenomena are that the eight-cell blastomere is physically excluded from the ICM by position or polarization, or that it is differentiating ahead of the two-cell component and becomes trophectoderm.

Animals↗
PubMed1987

Isolation and characterization of seminal fluid proteins that bind heparin.

Heparin facilities the acrosome reaction in bull and rabbit sperm. It binds to sperm saturably, and the binding affinity and the susceptibility to heparin are related to fertility. Isolation of heparin-binding proteins from washed ejaculated sperm reveals proteins mostly in the 14-18 kilodalton (kD) range. Seminal plasma inhibits heparin-induced capacitation, possibly by binding and inactivating heparin. These experiments focused on isolating and characterizing heparin-binding proteins in seminal plasma. Semen samples from 6 bulls were pooled, centrifuged twice for 10 min at 500 xg and finally at 2000 xg for 10 min. The supernatant was ultrafiltered on an Amicon YM-5 (5 kD cutoff) membrane against 40 mM Tris with 2 mM Ca2+ plus protease inhibitors. Five mg of protein were applied to a 1.5 x 10 cm column of heparin-Sepharose. Bound proteins were eluted with 200 ml of a 0 to 2 M NaCl gradient at 0.33 ml/min collecting 3 ml fractions. Two major peaks eluted at 0.12 and 0.46 M NaCl. Those were subjected to SDS-PAGE under reducing conditions. The 0.12 M peak was composed of small (mol wt 15.5 and 16.5 kD) polypeptides which were similar to those found on sperm. The 0.46 M peak included those polypeptides plus a 19.5 kD polypeptide and its trailing edge had a 29.5 kD polypeptide. These polypeptides may regulate capacitation by viture of their ability to bind heparin.

Animals↗
PubMed1987

Culture of one- and two-cell bovine embryos to the blastocyst stage in the ovine oviduct.

The ovine oviduct was evaluated as a culture system for early bovine embryos. One- to two-cell embryos were collected from superovulated heifers killed 36 or 48 h after the onset of estrus, embedded in agar cylinders, and transferred to oviducts ligated at the uterotubal junction. After 5 d (6.5 to 7.0 d after donor estrus), embryos were recovered and evaluated for development to the late morula or blastocyst stage. In Experiment 1, 86 embryos were cultured in 10 ewes in which the onset of estrus was synchronized with that of the donors. Fifty-eight embryos (68%) were recovered; of these, 31 (53%) had continued normal development. In Experiment 2, development in ovariectomized versus intact cyclic ewes was compared. Recovery from ovariectomized ewes (26/39, 67%) did not differ from intact cyclic ewes (26/35, 74%) and the proportion developing normally also did not differ (ovariectomized: 7/26, 27%; intact cyclic: 11/26, 42%). In Experiment 3, embryo development was compared in anestrous versus ovariectomized ewes. Recovery rate (anestrous: 22/43, 51%; ovariectomized: 20/51, 39%) and the proportion developing normally (anestrous: 8/22, 37%; ovariectomized: 9/20, 45%) did not differ between treatments. Developmental competence of oviduct-cultured embryos was tested by transfer to 16 synchronous heifers, of which eight (50%) became pregnant; five delivered calves. Results indicate that the ovine oviduct provides an adequate site for the culture of early bovine embryos.

Journal Article↗
PubMed1987

The effect of exogenous estradiol on litter size in a typical swine herd.

Fifty-six female pigs (12 gilts, 26 primiparous and 18 multiparous sows) were bred and assigned to receive either corn oil (vehicle; n=28) or estradiol-17beta (2 mg/day; i.m.; n=28) on Days 12 and 13 (Day 0=first day of estrus) to determine if exogenous estradiol could improve litter size in swine. Though litter size of the females farrowing was not increased with estradiol treatment (vehicle versus estradiol, 9.7+/-0.8 versus 10.1+/-1.8 live pigs born, respectively), more females in this group remained pregnant (vehicle versus estradiol, 6 versus 1 recycled, respectively; P<0.05). Litter size, expressed as the number of pigs born per-female-bred, was therefore increased with exogenous estradiol (vehicle versus estradiol, 7.6+/-0.8 versus 9.8+/-0.7 live pigs born, respectively; P<0.05). Some of these estradiol- treated females produced smaller (P<0.05) litters and this may be of concern in herds experiencing low fertilization/conception rates. Overall 60 more pigs were born alive to females in the estradiol-treated group than to the control group females. This experiment demonstrated that supplemental estradiol treatment on Days 12 and 13 assisted in maintenance of pregnancy and thereby increased litter size on a per-female-bred basis.

Journal Article↗
PubMed1987

Development potential of bovine oocytes matured in vitro or in vivo.

Bovine oocytes matured in vivo or in vitro were evaluated after sperm-oocyte incubation for frequency of sperm penetration, frequency of male pronuclei formation, and embryonic development. The frequency of sperm penetration was not different for in vitro matured oocytes (216/295, 73%) vs. in vivo matured oocytes (119/176, 70%). However, formation of male pronuclei was reduced (p less than 0.05) for oocytes matured in vitro (149/216, 69%) vs. in vivo (104/119, 88%). Early embryonic development was evaluated 48 h after the onset of sperm-egg incubations. In vitro matured and fertilized oocytes failed to develop to the 2-cell stage (3/88, 3%), whereas oocytes matured in vivo showed normal development (23/56, 40%) to the 2- and 4-cell stage. Development to the blastocyst stage was evaluated after 5 days in ovine oviducts (in vivo). Morulae and blastocysts were obtained only after in vitro fertilization from oocytes that were in vivo-matured (recovered from oviduct, 14/56, 25%; recovered from follicle, 36/80, 45%). Oocytes that were matured in vitro and fertilized in vitro failed to develop to morulae (0/33) in vivo.

Animals↗
PubMed1987

Nuclear transplantation in mouse embryos: assessment of nuclear function.

Enucleated mouse zygotes receiving eight-cell nuclei rarely develop beyond the two-cell stage, whereas enucleated two-cell embryos with eight-cell nuclei develop to blastocysts, and a few develop to midgestation. In this study the function of eight-cell nuclei in either the zygote or two-cell recipient was assessed by monitoring several nuclear-dependent events. These included methionine uptake, qualitative changes in protein synthesis, the time of blastocoele formation, and changes in nuclear volume. Although enucleated zygotes with nuclei from eight-cell embryos did not develop past the two-cell stage and had abnormally low levels of methionine uptake, they did show a normal zygote-to-two-cell transition in the types of polypeptides synthesized. Enucleated two-cell embryos with eight-cell nuclei formed blastocysts on schedule with the recipient cell stage and reached levels of methionine uptake equivalent to control embryos. The types of proteins synthesized by two-cell embryos with eight-cell nuclei indicated that the nucleus was developing partly in accord with its own developmental program. Transplanted nuclei did not enlarge to acquire the volume of the recipient cell's nucleus in either the zygote or the two-cell recipient. These results indicate that the difference in development between zygotes and two-cell embryos (each with eight-cell nuclei) may be the result of a greater overlap of function between the two-cell and eight-cell stages, rather than the extent of nuclear reprogramming. Nuclear function was not completely normal in either type of embryo, which may explain their failure to develop to term.

Animals↗
PubMed1987

Nuclear transplantation in the bovine embryo: assessment of donor nuclei and recipient oocyte.

Blastomeres from 2- to 32-cell bovine embryos were transferred to enucleated oocytes matured either in vivo or in vitro by micromanipulation and electrofusion. The percentage of donor cells fusing with the recipient oocytes was dependent on relative cell size or stage of development. Therefore, when smaller donor karyoplasts (17- to 32-cell vs. 2- to 8-cell) were transferred, the rate of fusion was significantly less (p less than 0.01). After fusion, nuclear transfer embryos were cultured either in vitro or in vivo (in a ligated ovine oviduct). Nuclear transfer embryos cultured in vitro developed to the 4- to 6-cell stage after 72 h (4-cell, 71%; 8-cell, 33%, 16-cell, 33%; p less than 0.30), whereas nuclear transfer embryos cultured in vivo developed to the morula or blastocyst stage (2- to 8-cell, 11.7%; 9- to 16-cell, 16.0%; 17- to 32-cell, 8.3%; p greater than 0.30) after 4 or 5 days. Freshly ovulated oocytes (collected 36 h after the onset of estrus), when used as recipients, resulted in morula/blastocyst-stage embryos more often than in vitro-matured oocytes or in vivo-matured oocytes collected 48 h after the onset of estrus (20% vs. 7.8% and 6.7%, respectively; p less than 0.02). After in vivo culture, nuclear transfer embryos were mounted and fixed or transferred nonsurgically to the uteri of 6- to 8-day postestrus heifers. Seven pregnancies resulted from the transfer of 19 embryos into 13 heifers; 2 heifers completed pregnancy with the birth of live calves.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Nuclear transplantation in bovine embryos.

This study was conducted to develop a method for transplanting nuclei in bovine embryos and to test the development of several stages of donor nuclei transplanted to enucleated pronuclear recipient embryos. Pronuclear embryos were centrifuged to reveal nuclei. Nuclei were removed without penetrating the plasma membrane as membrane-bound karyoplasts, and were inserted into enucleated zygotes by electrically induced cell fusion. The highest rate of fusion (79%) occurred in Zimmerman Cell Fusion medium at 100 V for 20 to 40 microseconds with the fusion membranes oriented parallel to the electrodes. The effect of nuclear transplantation on development was tested in pronuclear embryos in which nuclei were removed and reinserted and the embryos were then transferred to sheep oviducts for 5 d. Of the intact nuclear transplant embryos recovered, 5/29 (17%) developed to morulae or blastocysts compared with 11/30 (37%) of the non-manipulated embryos. Two nuclear transplant embryos were transferred to a recipient cow, and both developed to normal offspring. When nuclei from two-, four-, or eight-cell embryos were transplanted to pronuclear recipient embryos, no development was observed.

Animals↗