The zona pellucida (ZP) of mature pig oocytes is believed to consist of a dense filamentous meshwork, less compact on the inner and outer faces. The uneven surface of the ZP is made of unordered and stretched fibrils surrounding deep funnels which are the openings of the radial canaliculi. The topography of the ZP surface may contribute to the initial interplay between male and female gametes. Using cytochemical techniques for transmission electron microscopy (TEM), such as tannic acid and ruthenium red treatments, we found that the ZP of pig oocytes was essentially made of bundles of fibrils distributed in concentric layers (except in the innermost and outer parts). A correlation appears between the dense structure of the core layer of the ZP and its texture: it is constituted of superposed layers of fibril bundles, whereas only a random meshwork is found in a very thin innermost and in the outer layer. The fascicular configuration may control the permeability of the ZP, giving its semi-rigidity and elasticity, and may facilitate sperm penetration. The liquid crystal-like design of the core layer of the ZP is similar to textures found in the the vitelline envelope (zona radiata) of other vertebrates and possibly of all the deuterostomes. Such texture is probably related to the unique ZP protein composition and to a coordinated synthesis.

The extracellular matrix (ECM) of porcine mature oocytes was revealed by transmission electron microscopy (TEM) after treatment with tannic acid and ruthenium red. Present in the perivitelline space (PVS) and on the surface of the zona pellucida (ZP), it appeared to be composed of thin filaments and granules at the interconnections of the filaments, which were interpreted respectively as hyaluronic acid chains and bound proteoglycans. In order to determine whether this material is produced by the corona cells (the same ECM was found also on the surface of the zona pellucida and between cumulus cells) or by the oocyte itself, the synthesis of glycoproteins and glycosaminoglycans was checked by autoradiography on semi-thin and thin sections observed by light and electron microscopy. Immature oocytes within or without cumulus cells, were incubated with L [3H-] fucose or L [3H-] glucosamine – precursors respectively of glycoproteins and hyaluronic acid or hyaluronan (HA) bound to proteoglycans – for various times (with or without chase) and at different stages during in vitro maturation. In the first case, incorporation was found in both cumulus cells and ooplasm (notably in the Golgi area for 3H-fucose) and labeled material accumulated in the ECM of the PVS and of the ZP surface. Labeling in the PVS with both precursors was maximum between metaphase I (MI) and metaphase II (MII) and was partially extracted by hyaluronidase but not by neuraminidase. Tunicamycin, an inhibitor of glycoprotein synthesis, significantly decreased the amount of 3 H-fucose labeled molecules in the PVS and increased the incidence of polyspermic penetration during subsequent in vivo fertilization. Since cumulus-free oocytes also secreted 3 H-glucosamine containing compounds, both oocyte and cumulus cells probably contribute to the production of the ECM found in the PVS of mature oocytes. ECM and particularly its HA moiety present on both sides of the ZP may constitute a favourable factor for sperm penetration.

Nuclear bodies occuring during the 2-cell stage of bovine embryos (obtained either by in vitro fertilisation of in vitro matured ovarian oocytes, or collection after fertilisation and cleavage in vivo) were studied using ultrastructural cytochemistry and immunocytochemistry to determine whether their occurrence may be linked with the onset of embryonic transcription. In addition, the species-specific ultrastructural features of the interchromatin structures of the 2-cell bovine embryo were displayed. Three different types of nuclear bodies were distinguished: (i) nucleolus precursor bodies (NPBs), (ii) loose bodies (LBs) and (iii) dense bodies (DBs). In order to determine their possible functional significance, we considered parallels between these three nuclear entities and interchromatin compartments reported in other cells. As detected by their preferential ribonucleoprotein staining, all types of nuclear bodies contained ribonucleoproteins. In contrast to the other types of nuclear bodies studied, NPBs contained argyrophilic proteins but in no case they did show morphological features of functional nucleoli. Both compact and vacuolated forms of NPBs were seen in both in vivo and in vitro embryos, sometimes simultaneously in the same nucleus. LBs and DBs reacted with antibodies to Sm antigen, indicating the presence of a group of nucleoplasmic, non-nucleolar small nuclear ribonucleoproteins (snRNPs). The immunoreactivity for Sm antigen was more intense and homogeneous in DBs than in LBs. DBs were seen in both categories of embryo. A possible kinship of DBs with the sphere organelle known from oocytes of different animal species or the prominent spherical inclusions of the early mouse embryo nuclei is suggested. The last type of intranuclear body, the LBs, showed a composite structure. Their granular component, occurring in clusters and displaying immunoreactivity for Sm antigen, was similar to interchromatin granules and was therefore named IG-like granules. Another component forming the LBs showed a much finer structure and a lower immunoreactivity with anti-Sm antibodies. We suggest that this amorphous component may be related to the IG-associated zone. All three types of intranuclear bodies were often seen close together, suggesting their possible mutual functional relationship. From these and other observations we conclude that the intranuclear bodies in 2-cell bovine embryos correspond, with the exception of the NPB, to similar structures/compartments supposed to accumulate inactive spliceosomal components in certain phases of somatic cell nucleus functions. Accordingly, the occurrence of such nuclear bodies does not represent cytological evidence for RNA synthesis. In contrast to this, an important morphological feature revealing the status of the bovine 2-cell embryo is the vacuol-isation of the NPB.

Heifers (n = 9) of the Black-Pied Holstein-Friesian breed were slaughtered on the 3rd, Gth and 9th day of the synchronized cycle, respectively (heat = day 0). Tissue samples from the ampullar part of the oviduct were collected immediately after slaughter and treated for histoautoradiographic (ARG) analyses. They were cultured for 20 min on air in 0.25 ml medium Dulbecco PBS at 38 degrees C enriched with 100 mu Ci/ml of [5-H-3] uridine (specific activity 740 GBq/mM, UVVVR Prague) for detection of the RNA synthesis. For the ARG detection of glycoprotein synthesis the samples of oviductal tissue were cultured for 60 or 240 min on air, respectively, in 0.25 mi medium Dulbecco PBS at 38 degrees C to which 100 mu Ci/ml of L-[6-H-3] fucose (specific activity 0.55-1.1 TBq/mM, Amersham Int., Great Britain) was added. After incubation, the samples were fixed, dehydrated and embedded in Epon 812. Semithin (1 mu m) or ultrathin sections were coated with nuclear liquid emulsion K.5 or L.4, respectively. After one-month exposure they were developed using D 19 developer and after staining or contrasting they were observed using either light-microscopy or electron microscopy (using an electron microscope JEM 100 CX at 80 kV). Investigated autoradiograms revealed an intensive synthesis of RNA in both cilliated as well as in secretory cells of the oviduct epithelium. The intensity of RNA synthesis remains comparable during the early luteal phase from the 3rd to the 9th day of the cycle. The glycoproteins, synthesized first in the Golgi apparatus in the supranuclear region were seen to move to the apical region of the epithelial cells later on. The most intensive autoradiographic reaction of newly synthesized glycoproteins was detected on the 3rd day of the cycle without an evident change on the 6th day but decreasing on the 9th day.

Local application of /5-3H/uridine or /6-3H/thymidine to the cow ovary was obtained by the instillation of the radioactive solution into a rubber balloon ('bursa') tightly enclosing the organ exposed by laparotomy. After 30-90 min the exteriorized ovary was replaced in the abdominal cavity. Ovaries were recovered 1-8 days later and processed for autoradiography. After /5-3H/uridine application the peripheral layer of the ovary, containing the follicles in different stages of development was most intensely labelled. The labelling by /5-3H/uridine could be attributed prevailingly to the cytoplasm of different cells constituting the ovary but in some cases the labelling was higher in nuclei. The highest level of labelling was seen in the cytoplasm of follicular cells of follicles composed of one or two layers of cuboidal cells. Labelling was also detected in the ooplasm of oocytes with the maximal number of grains being seen in the first phase of their growth. On the other hand, no labelling was detected in the ooplasm of oocytes isolated from antral follicles the growth of which had been induced previously by hormonal treatment. It is believed that the labelling obtained by the described procedure represents to a significant degree RNA. A similar local application of /6-3H/thymidine allowed us to obtain labelling restricted specifically to nuclei of different cells composing the ovarian tissue. In the presented results, the entry of flattened follicular cells of primordial follicles in vivo in the S-phase of the cell cycle was demonstrated as well as an evident different proliferation rate in the successive stages of follicle development. The method proposed here may probably be the way for testing the effects of different substances, available only in small quantities, on the cow ovary.

In mammals, the restoration of rRNA transcription after fertilisation is accompanied by a gradual differentiation of the nucleolar structure by a process called embryonic nucleogenesis. During cleavage, the nucleolar components appear sterically related to a class of nuclear bodies already detectable in pronuclei. These structures, due to their apparent function as centres of nucleolus formation, have been designated nucleolus precursor bodies (NPBs). It was found recently not only that the size and morphology of the NPBs differ among mammalian species, but that the pattern of embryonic nucleologenesis and even the molecular composition of different NPB compartments vary from one species to another. Accordingly we assumed that at least two definitely different types of NPBs exist, namely the mouse-type NPB and cow-type NPB. In the mouse-type NPB, the original compact material of the NPB remains detectable in the early functional nucleolus. This NPB core does not contain DNA or typical Ag-NOR nucleolar proteins. At the onset of rRNA transcription, the nucleolonema is formed at the periphery of the NPB. The cow-type NPB shows a homogeneous distribution of typical nucleolar proteins throughout its body from the pronucleolar to the early 8-cell stage. At the beginning of rRNA transcription, the cow-type NPB is penetrated by perinucleolar DNA and rRNA synthesis is detectable deep inside the nucleolus. In this case, the entire NPB is readily transformed into a typical nucleolus. These processes are recognisable using fine-structure analysis of preimplantation mammalian embryos. For this reason this approach is often used as a method of evaluating the state of experimental embryos; in such studies, the species differences must be taken into account.

The developmental ability of hybrid zygotes, produced by in vitro fertilization of in vitro matured bovine oocytes with ram sperm, was evaluated by gross morphology, autoradiographic detection of (5‐3H) uridine incorporation, and fine structure morphology. Fertilization was successful in 83% of bovine oocytes inseminated with bull sperm (control embryos) compared with 67% of bovine oocytes inseminated with ram sperm (hybrid embryos) and in both cases appeared two regularly developed pronuclei. Two‐cell embryos were transferred to ewe oviducts and allowed to develop to the 8‐cell stage. Although the ability of hybrid embryos to reach 8‐cell stage was similar to that of control embryos, in nuclei of hybrid embryos the transition from maternal to embryonic genome control assessed according to the onset of RNA synthesis indicated the differences in the frequency of labelled nuclei and intensity of their labelling. In hybrid embryos these parameters were remarkably lower and may reflect the developmental failure of hybrid embryos. These observations are consistent with delay or inefficient reactivation of the embryonic genome in the hybrid embryos. Mol. Reprod. Dev. 48:344–349, 1997. © 1997 Wiley‐Liss, Inc.

Ultrastructural morphology and immunoelectron microscopy of the nucleus and nucleologenesis in early preimplantation cow embryos were applied in an attempt to demonstrate a possible radiation injury to that early stage of development due to chronical irradiation of the animals in the Tchernobyl area. Mostly eight cell embryos as well as morulae were collected from superovulated cows which were previously constantly kept in zones of different levels of radioactive irradiation. In addition to the normometric status of reproductive organs in no case was it possible to detect an apparent deviation in the nuclear morphology or in the process of nucleologenesis as compared to the physiological situation (Kopecny et al., 1989b, 1991, 1996). This observation was supported by an immunoelectron microscope study of DNA association and penetration in the differentiated nucleolus in the late 8-cell stage. These observations show that the otherwise demonstrated radiation injury localized in the genome does not probably influence markedly the early events of the developing embryo and that the aberrant cytoplasmic command of the nuclear events known in other types of oocyte/early cow embryo impairment (review Kopecny and Niemann, 1993; Kanka et al. 1991; Pavlok et al., 1993) is not seen in early embryos collected from chronically irradiated animals.

Ultrastructural morphology and immunoelectron microscopy of the nucleus and nucleologenesis in early preimplantation cow embryos were applied in an attempt to demonstrate a possible radiation injury to that early stage of development due to chronical irradiation of the animals in the Tchernobyl area. Mostly eight cell embryos as well as morulae were collected from superovulated cows which were previously constantly kept in zones of different levels of radioactive irradiation. In addition to the normometric status of reproductive organs in no case was it possible to detect an apparent deviation in the nuclear morphology or in the process of nucleologenesis as compared to the physiological situation (Kopecný et al., 1989b, 1991, 1996). This observation was supported by an immunoelectron microscope study of DNA association and penetration in the differentiated nucleolus in the late 8-cell stage. These observations show that the otherwise demonstrated radiation injury localized in the genome does not probably influence markedly the early events of the developing embryo and that the aberrant cytoplasmic command of the nuclear events known in other types of oocyte/early cow embryo impairment (review Kopecný and Nicmann, 1993; Kanka et al. 1991; Pavlok et al., 1993) is not seen in early embryos collected from chronically irradiated animals.

The aim of the present experiment was to analyze the chronology of pronucleus development and DNA synthesis, as well as the ultrastructure of intranuclear bodies, in bovine zygotes produced in vitro. Bovine oocytes were matured and fertilized in vitro, and sperm penetration and pronucleus development were examined. DNA synthesis was investigated by sequential incubation with [3H]- and [14C]thymidine followed by autoradiography on semithin sections. Ultrathin sections for transmission electron microscopy were prepared from the same zygotes. Sperm penetration was noted for the first time at 4 hr after in vitro insemination and reached a maximum at 6 hr. Pronucleus formation was initiated at 4 hr, and up to at least 11 hr the maternal pronucleus was more developed than its paternal counterpart. DNA synthesis was initiated at 14–15 hr, and the S-phase lasted for 8–10 hr. The most prominent ultrastructural entities of the pronuclei were the nucleolus precursor bodies (NPBs). During the S- and G2-phases, the NPBs spatially associated with clusters of interchromatin-like granules. The two components were firmly attached to each other by an electron-dense reticulum. During the late G2-phase, the NPBs were apparently detached from the interchromatin-like granules and the electron-dense reticulum again. The interaction between the intranuclear bodies and granules appears to be comparable with the situation previously described for in vivo-produced bovine zygotes (J Laurinčík et al., Mol Reprod Dev 43:62–69, 1996), except for the lack of vacuolization of the NPBs during the S-phase in vitro. Mol. Reprod. Dev. 50:192–199, 1998. © 1998 Wiley-Liss, Inc.

Fine structural cytochemistry and immunocytochemistry were used to study nucleic acids and nuclear proteins in nuclear bodies (NB) of pronuclear and 2-cell bovine and caprine embryos on ultrathin sections of paraformaldehyde fixed and Lowicryl K4M or LR White embedded specimens. The most striking feature detected in some of these nuclear bodies (NBs) was the presence of non-nucleolar proteins known to be involved in pre-mRNA splicing. One category of such intranuclear bodies (showing a rather dense finely fibrillar composition and named here dense body-DB) contained the Sm-antigen (an antigen common to a major group of nucleoplasmic spliceosomal snRNPs). Another, more numerous category of NBs differed morphologically from the former one by a much looser composition of fibrillogranular elements (loose body-LB). Moreover, it showed the presence of the non-snRNP splicing factor SC-35, in addition to the Sm-antigen. Both categories of these nuclear bodies were distinguished clearly from the nucleolar precursor bodies (NPBs) by an absence of immunolabeling of NPB with antibodies against nuclear proteins involved in splicing. Moreover, the former NBs are not stained with silver, while NPBs already in pronuclei exhibit strong affinity to silver. In addition to the immunolabeling in prominent (approx. 0.2-2.0 microns) NBs, regularly occurring high concentration of snRNP was revealed in very small (approx. 0.05 micron), morphologically poorly defined areas (named here small snRNP-enriched areas-SSA), harboring moreover a set of nuclear proteins similar to that of the coiled body. Numerous observations of the presence of these small areas in nuclear bodies and in their close vicinity, in nucleoplasm, in proximity of the nuclear envelope and also in ooplasm suggested that they are possible carriers of certain nuclear proteins moving between nuclear bodies, nucleoplasm and cytoplasm. A functional relationship of all these embryonic subnuclear elements has not been elucidated so far but their mutual relation is suggested, since the NPBs and other nuclear bodies usually occur in a close association. Fine structural and immunoelectron microscopic observations further suggest a similarity of the nuclear bodies in the early ruminant embryo with specific intranuclear bodies ("snurposomes") known from Xenopus laevis oocytes. A new and striking feature emerging from these observations is a possible involvement of a group of nucleoplasmic proteins in a yet unknown way in the differentiation processes concomitant with early embryonic nucleologenesis.

Germinal vesicle (GV) stage oocytes isolated from rat ovaries were investigated by immunoelectron microscopy for the presence of several nuclear proteins in the prominent 'compact nucleoli' (nucleolus-like bodies named here NLB). Specific spliceosomal components including the Sm antigen of the nucleoplasmic small nuclear ribonucleoproteins (snRNP) and the non-snRNP splicing factor SC-35 were clearly detected in the dense finely fibrillar mass of the NLB. Moreover, the presence of small nuclear RNA (snRNA) in the NLB was demonstrated by means of an antibody which recognized the m3G-capped snRNA. The level of immunolabelling for the nuclear proteins fibrillarin and p80-coilin was relatively lower in the NLB. p80-coilin was distinctly localized, in small, poorly morphologically defined structural constituents in the nucleoplasm. Aggregates of intranuclear granules having similar antigenic composition to the NLB were also detected. Our observations suggested that the 'compact nucleoli' of rat GV oocytes represented nuclear compartments containing significant amounts of non-nucleolar, spliceosomal components. These NLB have a molecular composition closer to the composition of certain nuclear bodies than to the functional nucleoli of somatic cells. The NLB may represent a compartment in the mammalian oocyte, akin to the sphere organelle of the amphibian oocyte (also reported to contain spliceosomal components and a p80-coilin-related protein). Both structures may serve as temporary storage organelles for different maternal macromolecules, which support early embryonic development, inter alia of that involved in the maturation of pre-mRNA to be transcribed from the embryonic genome.

The fine structure of pig oocytes at the germinal vesicle (GV) stage and early preimplantation embryos (one to four blastomeres) isolated at slaughter was investigated by cytochemical and immunocytochemical methods. The distribution of nucleic acids and ribonucleoproteins (RNPs) in "compact nucleoli" [denominated nucleolus-like bodies (NLB) in oocytes and nucleolus precursor bodies (NPB) in early embryos] and in intranuclear bodies or granules was investigated by staining methods preferential for nuclear RNPs or using the osmium ammine or ethidium bromide-phosphotungstic acid (EB-PTA) reactions for nucleic acids. The distributions of the Sm antigen of nucleoplasmic small nuclear RNPs (snRNPs), the methyl-3 guanosine (m3G) cap of snRNAs and the splicing factor SC-35 were detected by immunoelectron microscopy using specific antibodies. The RNP nature of both NLBs and NPBs, and of nuclear granules in oocytes and embryos, and of fibrillar strands radially projecting from NLBs was revealed. Cytochemical evidence for RNA as a component of NLBs was further provided by EB-PTA staining in combination with the enzymatic removal of RNA, or by osmium-ammine staining without previous acid hydrolysis, while the absence of DNA in NLBs was established by Feulgen-like osmium-ammine staining. In addition, autoradiography demonstrated the absence of [6-3H]thymidine incorporation into NPBs. Other autoradiographic evidence attested the accumulation of RNA in NLBs of oocytes after a 60 min in vitro pulse of [5-3H]uridine. Immunoelectron microscopy using specific antibodies revealed the occurrence of nucleoplasmic snRNPs in both NLBs and NPBs. The presence of snRNA in NLB was confirmed by means of an antibody recognizing the m3G-cap structure. Another spliceosomal component, the protein SC-35 was also detected in NLBs. Among the numerous and variable intranuclear granules occurring mostly in aggregates, the Sm antigen was clearly detected only in the interchromatin granule-type component. Some Sm labeling was occasionally seen in other categories of larger granules. No reaction was detected over any granules when using the anti-m3G-cap antibody. The aggregates consisting of large granules and a finely fibrillar component were intensely immunolabeled by the anti-SC-35 splicing factor probe. Our observations suggest that the compact nucleoli, known to be present before and after fertilization in mammals (NLBs of oocytes and NPBs of early embryos), represent nuclear structural elements containing nonnucleolar, spliceosomal components.

Parthenogenetically activated, in vitro-matured bovine oocytes and parthenogenotes obtained at 2 to 4 days post activation were analyzed by 3H-thymidine autoradiography for the timing of the S-phase and for distribution of newly replicated DNA, respectively. Spread pronuclear parthenogenotes revealed that the DNA synthesis in electrically stimulated oocytes commenced at 14 h post activation. At 20 to 24 h, a maximum number of labeled pronuclei was reached (25 to 38%), and DNA synthesis persisted in some parthenogenotes up to 30 h post activation. The DNA labeling detected on semi-thin sections showed that the distribution of newly synthesized DNA in the nuclei of 3- to 16-cell parthenogenotes was mostly irregular or abnormal, documenting that the apparent morphological normalcy of parthenogenotes was in contrast to the data concerning the DNA synthesis and distribution.

Mouse preovulatory oocytes, zygotes, parthenogenetically activated pronuclear oocytes, and early embryos, as well as hamster zygotes, were analyzed, by autoradiography, for the distribution of either "maternal" or newly synthesized RNAs. Early mouse embryos were also examined for the distribution of newly replicated DNA. Special attention was attributed to NLBs in oocytes or to NPBs in early embryos. In mouse oocytes, [5-(3)H]uridine radioactivity accumulated (after a 2-hr pulse in vitro, in addition to other nuclear compartments, in the central compact material of the NLBs. There was no cytoplasmic labeling. In all parthenogenetic pronuclear embryos developed from similarly labeled oocytes, this label was distinctly detectable in the central compact material of the NPBs; less intensive labeling was seen in the nucleoplasm and cytoplasm. On the contrary, the central compact part of the mouse NPB did not show labeling in DNA after a continuous culture with [6-(3)H]thymidine. In mouse and hamster pronuclear zygotes, convincing evidence was obtained for a lack of any newly synthesized nucleic acids in the compact material of NPBs using 4- to 10-hr culture with [8-(3)H]adenosine. Based on these data, it was shown that the NLBs of oocytes or NPBs of early embryos probably contain RNAs synthesized during the last stages of antral follicle oocyte differentiation. This unique pathway of RNAs in the oocyte-embryo system may explain the specific morphology of both oocyte and early embryo "nucleoli".

Porcine zygotes flushed from oviducts 48, 52, 56, 60, or 64 hr after hCG were incubated 30 min in 3H-thymidine, transferred to nonradioactive medium for 2 hr, and incubated for 30 min with 14C-thymidine. After this procedure, ova were prepared (i.e., at 51, 55, 59, 63, or 67 hr after hCG) for autoradiography and ultrastructural observations, respectively. The first autoradiographic labelling, i.e., DNA synthesis, was observed at 56-56.5 hr after hCG, while the latest labelling was seen at 60-60.5 hr. At 51 hr after hCG, formation of the pronuclear envelope was observed, while no nucleolus precursor bodies or prestages to these structures were found. At 55 hr a few clusters of small electron-dense granules were observed, together with condensed chromatin in the pronuclei. At 59 hr the apposed regions of both pronuclei contained nucleolus precursor bodies and condensed chromatin, in close contact with both clusters of small granules and clusters of an additional category of large granules and the nuclear envelope. Additionally, large accumulations of the small granules were found in the vicinity of similarly sized accumulations of the large granules without chromatin association. At 63 hr the spherical accumulations of large granules on some occasions presented a central vacuole, and condensed chromatin and clusters of small granules were attached to its periphery. Within the vacuole, electron-dense material was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Early preimplantation goat embryos were investigated for the onset of major gene transcription by fine-structure morphology and autoradiographic detection of (5-(3)H)uridine incorporation. Complex nuclear bodies were already seen in early pronuclei but only in the 16-cell embryos did these methodologies offer clear-cut evidence of the already fully-developed nucleolar structure as well as of nucleoplasm labeling. Nucleoplasm labeling, which is supposed to detect the onset of major transcription, was absent in the pronuclear and the 2- to 4-cell embryos. The first (5-(3)H)uridine incorporation was detected in the 8-cell stage nuclei nucleoplasm, followed by nucleolar labeling. Based on this evidence, we found that in comparison with other ruminants, there is no striking difference in the timing of the shift in control from the maternal to the embryonic genome in the development of the early goat embryo.

Parthenogenetically activated, in vitro — matured bovine oocytes and parthenogenotes obtained at 2 to 4 days post activation were analyzed by 3H-thymidine autoradiography for the timing of the S-phase and for distribution of newly replicated DNA, respectively. Spread pronuclear parthenogenotes revealed that the DNA synthesis in electrically stimulated oocytes commenced at 14 h post activation. At 20 to 24 h, a maximum number of labeled pronuclei was reached (25 to 38%), and DNA synthesis persisted in some parthenogenotes up to 30 h post activation. the DNA labeling detected on semi-thin sections showed that the distribution of newly synthesized DNA in the nuclei of 3- to 16-cell parthenogenotes was mostly irregular or abnormal, documenting that the apparent morphological normalcy of parthenogenotes was in contrast to the data concerning the DNA synthesis and distribution.

Cell Biology InternationalVolume 17, Issue 6 p. 615-617 Association of plasmid pKT3 with cock spermatozoa in two different temperatures. Pavel Trefil, Corresponding Author Pavel Trefil Research Institute of Animal Production, Prague 10-Uhříněves.Corresponding authorSearch for more papers by this authorJosef Mika, Josef Mika Research Institute of Animal Production, Prague 10-Uhříněves.Search for more papers by this authorDaniel Slíva, Daniel Slíva Research Institute for Veterinary Drugs, Jílové near Prague.Search for more papers by this authorVáclav Kopečný, Václav Kopečný Research Institute of Animal Production, Prague 10-Uhříněves.Search for more papers by this author Pavel Trefil, Corresponding Author Pavel Trefil Research Institute of Animal Production, Prague 10-Uhříněves.Corresponding authorSearch for more papers by this authorJosef Mika, Josef Mika Research Institute of Animal Production, Prague 10-Uhříněves.Search for more papers by this authorDaniel Slíva, Daniel Slíva Research Institute for Veterinary Drugs, Jílové near Prague.Search for more papers by this authorVáclav Kopečný, Václav Kopečný Research Institute of Animal Production, Prague 10-Uhříněves.Search for more papers by this author First published: June 1993 https://doi.org/10.1006/cbir.1993.1107AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume17, Issue6June 1993Pages 615-617 RelatedInformation