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J Petr

Publications and source records attributed to J Petr.

At least 37 records · Page 2Linked to original sources
PubMed1995

Microtubule rearrangement during in vitro maturation of pig oocytes. Effect of cycloheximide.

In freshly isolated fully grown pig oocytes at the germinal vesicle (GV) stage, the cytoplasmic microtubules are arranged in a meshwork. This microtubule arrangement is also maintained during the initial phases of meiotic maturation in vitro. A perinuclear array of microtubules is formed immediately before germinal vesicle breakdown (GVBD). Short-term treatment of oocytes with taxol when oocytes are at metaphase I stage induced formation of cytoplasmic asters. The oocyte cytoplasm is unable to respond to the taxol treatment at the earlier stages of meiotic maturation. In oocytes cultured with the proteosynthesis inhibitor cycloheximide, meiotic maturation is blocked. Condensation of chromatin occurs but the nuclear envelope is preserved and the microtubule arrangement is unchanged. A perinuclear array of microtubules does not appear and oocyte cytoplasm does not respond to short-term taxol treatment by the formation of cytoplasmic asters. We can conclude that the microtubule rearrangement and the acquisition of competence for tubulin assembly are blocked by cycloheximide and are thus dependent on de novo proteosynthesis.

Animals↗
PubMed1994

Cytoplasmic argyrophilic protein(s) in cumulus-oocyte complexes: a preliminary study.

The presence of acidic argyrophilic protein(s) in cumulus cells and oocytes was examined in bovine, ovine, porcine and murine cumulus-oocyte complexes (COCs) using a specific silver-staining method. The COCs were isolated from small (1 mm) or large (3-5 mm) antral follicles; they were fixed immediately after slaughter (first group) or after transfer to the laboratory (ca 60 min, second group) and then silver stained according to Likovskí and Smetana (1981). The argyrophilic proteins were accumulated mainly in foot processes of cumulus cells on oocytes isolated from large bovine follicles. The intensity of the reaction was less evident in small follicles. The intensity of staining gradually disappeared from cumulus cells as the maturation continued. Moreover, we were unable to detect similar strong labelling in mouse, pig and sheep COCs. Such a chronology suggests that argyrophilic protein(s) may play a role in the transition from meiotic arrest to resumption in bovine oocytes. Our results also suggest that preliminary events of maturation may occur just after slaughter, ie a relatively long time before the COCs are isolated and cultured in vitro.

Animals↗
PubMed1994

Influence of cytoplasmic microinjection on meiotic competence in growing pig oocytes.

It is demonstrated that the microinjection of cytoplasm from competent, fully grown oocytes can induce germinal vesicle breakdown in meiotically incompetent growing oocytes. Injection of cytoplasm from oocytes at methaphase I had a similar effect. The maturation in injected growing oocytes was arrested at the premetaphase or metaphase I stage. Induction of germinal vesicle breakdown by cytoplasm microinjection occurs in a dose-dependent manner.

Animals↗
PubMed1994

Inhibition of meiotic maturation in growing pig oocytes by factor(s) from cumulus cells.

Total inhibition of germinal vesicle breakdown (GVBD) was observed in growing pig oocytes (internal diameter 80, 90 and 100 microns) when they were cultured in a medium conditioned by cumulus oocyte complexes (COCs) of fully grown oocytes. In denuded growing oocytes, only partial inhibition was observed. The inhibitory effect was fully reversible. The addition of heparin (300 IU/ml) could overcome the effect of the conditioned medium. Transient exposure (6 h) of oocytes to dibutyryl cyclic adenosine monophosphate (dbcAMP) (1 mg/ml) could also partly reverse the effect of factor (s) produced by cumulus cells of fully grown oocytes. Follicle-stimulating hormone (5 micrograms/ml) was able to increase the percentage of maturing oocytes. The addition of luteinizing hormone (5 micrograms/ml) had no effect on GVBD inhibition by cumulus-conditioned medium.

Animals↗
PubMed1991

Nuclear transplantation in bovine embryo: fine structural and autoradiographic studies.

Nucleolar fine structure, "blebbing" activity of nuclear envelope, and activation of heterogeneous nuclear RNA (hnRNA) synthesis were studied in bovine reconstructed embryos obtained by electrofusion of a single eight-cell blastomere with an enucleated oocyte. Developmental progress of nucleolar fine structure and hnRNA synthesis are arrested during three cell cycles following fusion. The activation of both appears during the eight-cell stage of the reconstructed embryo, after the same number of cell cycles after fusion as in nonmanipulated bovine embryos after fertilization. "Blebbing" activity of nuclear envelope, which is already absent in original blastomeres, reappears after fusion and continues for the next two cell cycles. From the present results, it can be concluded that the donor nuclei are arrested after fusion in morphology and function. Their reactivation corresponds to the developmental pattern typical for normal bovine embryos.

Animals↗
PubMed1991

Influence of dbcAMP on the inhibitory effect of cumulus cell factor(s).

The factor(s) produced by porcine cumulus cells (cumulus cell factor (s): CCF) was described as quantitatively inhibiting the maturation of oocytes in vitro (Petr et al, 1989). When 1, 10, 20 or 40 cumulus oocyte complexes (COCs) were cultured in a droplet of medium (vol 10 microliters), germinal vesicle breakdown (GVBD) was observed in 85, 78, 57 or 19% of the oocytes, respectively. GVBD was observed in 82, 84, 80 or 90% of cumulus-free oocytes, respectively, when they were cultured at the same numbers per 10-microliters droplet. When 1, 10, 20 or 40 cumulus-free oocytes were cultured under the same conditions in a medium containing 140 dbcAMP per ml, 61, 63, 60 or 58% of them were observed at GVBD. However, when COCs were cultured in a 10 microliter droplet of medium with 140 micrograms of dbcAMP per ml, GVBD occurred in 64, 42, 9 or 0% respectively. Based on these results, we can conclude that dbcAMP exerted a further inhibitory effect on GVBD in pig oocytes cultured under the influence of inhibitory factor(s) from cumulus cells. On the other hand, dbcAMP was shown to partly overcome the effect of CCF on GVBD in porcine oocytes. This suggestion was based on the finding that a 6-h pre-culture of COCs in a medium with 1,000 micrograms of dbcAMP significantly decreased the subsequent effect of CCF (GVBD: 44%) compared with those pre-cultured in a medium with 140 micrograms of dbcAMP/ml (GVBD:5%) or without dbcAMP (GVBD: 15%).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Ultrastructural localization of basic lysine-rich proteins during the nucleologenesis in preimplantation mouse embryos.

The paper describes nucleologenesis in preimplantation mouse embryos studied by electron microscopy after staining with ethanolic phosphotungstic acid (E-PTA), a substance which binds to basic lysine-rich proteins and makes it thus possible to follow their localization and distribution. A nucleolar precursor body (NPB) homogeneously stained with E-PTA first appears in pronuclei of a fertilized oocyte. In 2-cell stage embryos, the staining intensity of the central part of NPB is reduced, whereas the outer zone retains the PTA positivity. In the course of further development, reticulation takes place in the peripheral zone and all structures of a functional nucleolus are gradually formed. Tiny spherical bodies, called "remnant NPBs", can still be observed in reticular nucleoli of cells at the morula stage. The similarities in reaction and morphological appearance of the NPB and the corresponding structures in oocytes of the mouse and rat antral follicle are discussed.

Animals↗
PubMed1990

The effect of PMSG-priming on subsequent superovulatory response in dairy cows.

Superovulation was induced in 56 dairy cows to evaluate the effect of two different regimens using pregnant mare serum gonadotropin (PMSG). Thirty-two cows (controls) were superovulated between Days 9 and 12 of the estrous cycle with a single dose of PMSG (2 800 IU), while remaining 24 cows (PMSG-primed) received 200 IU of PMSG on Day 4 of the estrous cycle and subsequently a single dose of PMSG (2 800 IU) between Days 8 and 12. The cows in both treatments were each given 0,5 mg of cloprostenol at 48 h after the superovulatory PMSG treatment. They were then artifically inseminated twice, 48 h and 72 h later. Embryos were recovered at sloughter between Days 2 and 5 of the cycle and morphologically evaluated. The number of corpora lutea (CL) in the ovaries of the cows was recorded. The mean number of CL (7.2 vs 17.8) was significantly higher (P 0.01) for PMSG-primed cows. The percentage of recovered ova (60.5 vs 70.2 %) and good embryos (79.3 vs 70.7%) were not significantly different between groups. The percentage of fertilized ova (91.4 vs 83.8%) was significantly (P 0.025) greater for the controls. Results of the study indicate that PMSG-priming increased the ovulation rate in the cows superovulated with PMSG.

Journal Article↗
PubMed1989

Quantitative inhibitory influence of porcine cumulus cells upon the maturation of pig and cattle oocytes in vitro.

Porcine cumulus oocyte complexes (COCs) were cultured together in 10-microliters droplets of culture medium. When 10 COCs were cultured for 24 h, germinal vesicle breakdown (GVBD) occurred in 81% of them. When more COCs (20 or 40) were put into the same volume of medium the frequency of GVBD gradually decreased. This inhibition was not observed in denuded oocytes. The process of GVBD was adversely influenced when 10 COCs were cultured in cumulus-preconditioned medium. It is concluded that porcine cumulus cells produced a factor inhibiting GVBD. After removing the inhibitory block and extensive washing, GVBD of arrested oocytes was significantly accelerated. The addition of LH or heparin only partially overcame the inhibitory action. This factor produced by porcine cumulus cells negatively influenced maturation of bovine oocytes; however, a similar effect was not demonstrated in the mouse. Our results suggest that a high concentration of porcine cumulus cells exerts a quantitative inhibitory effect upon GVBD of porcine and cattle oocytes cultured in vitro.

Animals↗
PubMed1989

Localization of replicated DNA-containing sites in preimplantation bovine embryo in relation to the onset of RNA synthesis.

The distribution of embryonic DNA in nuclei of blastomeres of early-preimplantation cow embryos was studied by autoradiography. Two-, 4-, 8-, and 16-cell embryos were cultured for 18-20 h in the presence of [methyl-3H]thymidine to ensure that all replicated embryonic DNA was labeled. In nuclei of blastomeres before the onset of transcription, taking place in the progressed 8-cell cleavage division of the cow embryo, labeled DNA was distributed excentrically at the nuclear periphery. After transcription started, the distribution of the labeled DNA was uniform throughout the nucleus. The progressive association of DNA with the nucleolus-precursor body (NPB) also correlated with the expected onset of rRNA synthesis. The penetration of the labeled DNA into NPB was seen to start contemporaneously with the formation of a big central vacuole in NPB, but remained restricted, at this stage, to a few points of contact with the adjacent nucleolus-associated chromatin. No labeled DNA was detected inside this big vacuole, still showing a uniform nucleoplasmic texture. The inside of the nucleolus was penetrated by DNA in the next step of nucleologenesis when secondary small vacuoles were formed and when the first signs of nucleolar transcription were detected. These small vacuoles contained a coarse fibrillar component which was a frequent site of labeled DNA detection. This study of shifts of DNA-containing sites during transition from maternal to embryonic genome expression correlates closely with previous evidence obtained by a study of genome reactivation which was situated in the late 8-cell cleavage division of cattle early embryogenesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Effect of ascorbic acid prophylaxis on the frequency of chromosome aberrations, urine mutagenicity and nucleolus test in workers occupationally exposed to cytostatic drugs.

The genetic risk of workers occupationally exposed to a series of newly developed cytostatic drugs and the presumed antimutagenic potential of ascorbic acid (AA) were studied in a group of 38 chemical laboratory personnel examined for chromosome aberrations in lymphocytes, urine mutagenicity and nucleolar RNA activity before and after a 6-month prophylactic administration of AA at daily doses of 1 g for 5 days a week. Chromosome aberration tests revealed elevated aberrant cell (AB.C) rates both prior to and after AA supplementation (3.9% and 3.65% of AB.C., respectively). These values were significantly higher than those found in 18 non-exposed matching controls (1.05% of AB.C.). Tests for mutagenic activity in the urine of drug-exposed workers revealed 64% positive urine samples prior to vitaminization and 60% positive urine specimens after it; positive urine samples in the group of controls accounted for 21% of samples. In the nucleolus test, numbers of inactivated micronuclei in the exposed were initially higher than those of controls (33.4% versus 24.3%), but dropped to 20.5% after AA supplementation. These findings show that AA prophylaxis alone cannot substantially reduce the hazards associated with exposure to anti-cancer drugs.

Antineoplastic Agents↗
PubMed1988

Twenty-four hour pattern of lutropin and progesterone pulsatile secretion base line in postpartum dairy cows.

Twenty-four hour patterns of lutropin and progesterone pulsatile secretion base line were studied in six postpartum dairy cows. The base line of lutropin showed three peaks within 24 hours. The base line of progesterone showed two peaks which coincided in the time with the nadirs of lutropin base line. These peaks show up clearly irrespective of the stage of puerperium.

Animals↗