Nucleolar changes in bovine nucleotransferred embryos

This study focused on nucleolar changes in bovine embryos reconstructed from enucleated mature oocytes fused with blastomeres of morulae or with cultured, serum unstarved bovine fetal skin fibroblasts (embryonic vs. somatic cloning). The nucleotransferred (NT) embryos were collected and fixed at time intervals of 1-2 h (early 1-cell stage), 10-15 h (late 1-cell stage), 22-24 h (2-cell stage), 37-38 h (4-cell stage), 40-41 h (early 8-cell stage), 47-48 h (late 8-cell stage), and 55 h (16-cell stage) after fusion. Immunocytochemistry by light and electron microscopy was used for structure-function characterization of nucleolar components. Antibodies against RNA, protein B23, protein C23, and fibrillarin were applied. In addition, DNA was localized by the terminal deoxynucleotidyl transferase (TdT) technique, and the functional organization of chromatin was determined with the nick-translation immunogold approach. The results show that fully reticulated (active) nucleoli observed in donor cells immediately before fusion as well as in the early 1-cell stage after fusion were progressively transformed into nucleolar bodies displaying decreasing numbers of vacuoles from the 2- to 4-cell stage in both types of reconstructed embryos. At the late 8-cell stage, morphological signs of resuming nucleolar activity were detected. Numerous new small vacuoles appeared, and chromatin blocks reassociated with the nucleolar body. During this period, nick-translation technique revealed numerous active DNA sites in the periphery of chromatin blocks associated with the nucleolar body. Fully reticulated nucleoli were again observed as early as the 16-cell stage of embryonic cloned embryos. In comparison, the embryos obtained by fetal cloning displayed a lower tendency to develop, mainly during the first cell cycle and during the period of presumed reactivation. Correlatively, the changes in nucleolar morphology (desegregation and rebuilding) were at least delayed in many somatic NT embryos in comparison with the embryonic NT group. It is concluded that complete reprogramming of rRNA gene expression is part of the general nuclear reprogramming necessary for development after NT.

Modulation of protein synthesis in rabbit inner cell mass-derived cells by FGF-2

Gastrulation is a critical step in vertebrate development, that depends on synergistic effects of several signalling molecules, including fibroblast growth factor-2 (FGF-2). To follow this phenomenon in vitro we isolated rabbit inner cell masses (ICMs) at embryonic day 4 and we exposed ICM-derived cells to FGF-2. Then, we analysed the quantitative differences in rates of protein synthesis from day 3 to day 5 of culture by two-dimensional (2D) gel electrophoresis. Here we show that both up- and down-regulation of protein synthesis took place in ICM-derived cells upon their exposure to FGF-2. The effect of FGF-2 was most pronounced at day 4 of culture, when the changes were very much in favour of a set of down-regulated proteins. To test the significance of this period of time for FGF-2-mediated regulation of protein synthesis, cells were grown without FGF-2 and then they were pulse-treated with FGF-2 at the end of day 4. When compared to the continuous culture with FGF-2, the FGF-2 pulse resulted in a quite indistinguishable pattern of up- and down-regulated proteins. Thus, the readiness of ICM-derived cells to accept and respond to the FGF-2 signals may be of limited duration.

Comparative immunohistochemical distribution of connexin 37 and connexin 43 throughout folliculogenesis in the bovine ovary

Among gap junctional proteins previously identified in the mouse ovary, connexins (Cx) Cx37 and Cx43 appeared to be essential for normal follicular growth. The aim of this work was to detect Cx37 expression in the bovine ovary, then to quantify and compare its follicular distribution pattern with that of Cx43 using quantitative analysis of immunofluorescently labeled ovary sections viewed with a confocal laser scanning microscope. Cx37 immunoreactivity was detected in bovine ovarian follicles and was predominantly localized at preantral stages. Unlike follicular Cx43 expression which was restricted to granulosa cells, Cx37 staining was observed in both oocyte and granulosa cell compartments. While no changes were seen during early follicular growth, the level of Cx37 expression decreased significantly at the onset of antral cavity formation (P Collapse

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MESH Headings

• Animals
• Cattle
• Connexin 43/metabolism
• Connexins/metabolism
• Female
• Fluorescent Antibody Technique, Indirect
• Ovarian Follicle/growth & development
• Ovarian Follicle/metabolism
• Ovarian Follicle/pathology
• Tissue Distribution
• Gap Junction alpha-4 Protein

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Affiliation(s)

F Nuttinck Unité de Biologie du Développement, Institut National de Recherche Agronomique, Jouy-en-Josas, France
N Peynot
P Humblot
A Massip
F Dessy
J E Fléchon

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Immunocytochemical characterisation of rabbit and mouse embryonic fibroblasts

By using indirect immunofluorescence we demonstrated the localisation of extracellular matrix (ECM) proteins (laminin--LAM, collagen IV--COL IV, fibronectin--FN) and the basic fibroblast growth factor (bFGF) in rabbit and mouse primary embryonic fibroblasts (PEF). Proliferating mitotically arrested PEF (by mitomycin C) were compared in both species. The stability of protein expression was ascertained during the first five successive passages. In addition, STO cells (i.e. permanent line of irradiated mouse fibroblasts) were similarly analysed. Rabbit PEF showed very high extracellular staining for FN and a negligible cytoplasmic positivity for LAM and COL IV. A totally reversed staining pattern for ECM proteins was found in mouse PEF. A dense cytoplasmic granulation (concentrated around the nucleus) was revealed for LAM and COL IV and almost no reaction for FN. The staining patterns were very stable at the culture conditions we applied. They were maintained during the first five successive passages in proliferating as well as non-proliferating mouse and rabbit PEF and were independent of cell concentration (individually dispersed cells versus cells in a confluent layer). STO cells showed the same staining for ECM proteins as the mouse PEF, thus confirming their origin from the same animal species. Light granular staining for bFGF was found in the cytoplasm of proliferating and mitotically arrested rabbit and mouse PEF and STO cells. The differences in expression of ECM proteins between the rabbit and mouse PEF, as well as the synthesis of bFGF, should be taken into consideration when these cells are used in vitro as a feeder layer for various cells (e.g. embryonic stem cells).

Developmental potential of bovine embryos reconstructed from enucleated matured oocytes fused with cultured somatic cells

Muscle and skin biopsies taken from bovine fetuses and young calves have been used as a source of donor nuclei for cloning experiments. After culture, cells were individually fused to enucleated matured oocytes and the resulting blastocysts obtained after 7 d of culture (3-8% depending on the cell type) were transferred to foster recipient heifers. Two calves, a female and a male, both originating from muscle cells were born, and four additional pregnancies have surpassed mild-term gestation. The pregnancies include one fetus established from a transgenic nucleus from a fetal skin cell, and another one resulting from a skin biopsy performed on a female calf. Our data demonstrate that nuclei from cultured bovine somatic cells obtained from differentiated tissues can be made multipotent.

The nature of the 'nucleolus precursor body' in early preimplantation embryos: a review of fine-structure cytochemical, immunocytochemical and autoradiographic data related to nucleolar function

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.

Nucleolar substructures of rabbit cleaving embryos: an immunocytochemical study

The structure-function relationships of the nucleolar substructures were studied in preimplantation rabbit embryos, where nucleologenesis is extending over the first four cell cycles and may not be synchronous in each blastomere. Immunocytochemical methods using light and electron microscopy were applied for protein and RNA localization as well as nick translation and terminal deoxynucleotidyl transferase techniques for DNA detection. DNA was gradually associated with the periphery of the compact nucleolar precursor bodies (NPBs) but was never found inside NPBs at the four-cell stage. In 16-cell embryos, some NPBs displayed a reticulated periphery forming the branching network of the dense fibrillar component (DFC) surrounding the "residual body" (remnant of NPB) in the process of activation. At the 32-cell stage, fully reticulated nucleoli were observed in each blastomere. DNA was then associated with the DFC of reticulated nucleoli. RNA was first detected at the 16 cell-stage in close contact with the DFC as well as inside the "residual body" which was not immunolabeled with the DNA antibodies used. When observed by light microscopy, fibrillarin, nucleolin, and protein B23 displayed a changing distribution pattern during nucleologenesis. At early stages (up to the 16-cell stage), small dot- and spot-like structures were distributed within the whole nuclei. In 16-cell embryos, these proteins started to accumulate in an irregular thin layer around the NPBs in the process of activation. The reorganization process described may be in relation with the redistribution of chromatin and nuclear/nucleolar matrix components during the activation of rDNA transcription localized in the NPB shell. In conclusion, nucleologenesis is only achieved at the fourth cell cycle in the cleaving rabbit embryo at the corresponding time when the first detectable nucleolus-associated RNA is detectable. Our results show a good correlation between the establishment of structure and function.

Ultrastructural and immunocytochemical analysis of diploid germ cells isolated from fetal rabbit gonads

Germ cells were isolated from rabbit fetal gonads between 18 and 22 days post coitum and examined morphologically, ultrastructurally and for immunocytochemical and cytochemical characteristics. Observations were compared with the information available from the corresponding cells of other mammalian species. The general morphology and ultrastructure of healthy isolated rabbit fetal germ cells were found to be very similar to those of the rabbit and mouse diploid germ cells in situ. Moreover, rabbit fetal germ cells shared common immunocytochemical characteristics with mouse undifferentiated embryonic stem cells or embryonic carcinoma cells, such as the presence of TEC-1 (SSEA-1) antigens, a peripheral network of F-actin, the absence of cytokeratins 8/18 and lamins A/C and an alkaline phosphatase activity. No difference between the sexes was observed. Morphological and physiological similarities with the migrating and cultured primordial germ cells of the mouse also suggest that diploid rabbit germ cells would be good candidates for deriving pluripotential embryonic germ cells (EG cells) if favourable culture conditions could be found. In conclusion, the rabbit may be a suitable model for investigations on EG cells in domestic mammals with delayed meiosis.

Differential ability of male and female rabbit fetal germ cell nuclei to be reprogrammed by nuclear transfer

The pluri- or totipotency of gonial cells, isolated from rabbit fetuses at 18-20 days of pregnancy, has been investigated by transferring their nuclei into enucleated oocytes and following the development of the resulting reconstituted embryos both in vitro (in a total of 726 embryos) and in vivo (in 135 embryos). The gonial cells exhibited pseudopodial activity like that of primordial germ cells and ultrastructural studies confirmed that neither male nor female cells had entered meiosis. When the gonial cells were used immediately after isolation, about 37% of the reconstituted embryos of both sexes cleaved, with no significant difference according to sex. However, after a further 4-day culture of the cleaved embryos, the blastocyst formation rate was four times higher in those made with male (16%) than with female (4%) gonial cells. No implantation sites were detected following transfer of reconstituted embryos into recipient females. These results show that the nuclei of male and female rabbit diploid germ cells differ in their capability to be "reprogrammed" and bring about development to the blastocyst stage following nuclear transfer. The origin of this difference, which is evidenced long before the onset of meiosis is discussed.

Nucleologenesis in the cleaving bovine embryo: immunocytochemical aspects

In vivo nucleologenesis was studied in bovine embryos by electron microscopic immunogold labelling of DNA, RNA, protein C23 and protein B23. We have used the classification of Kopecný et al. (1989b) and Kopecný (1990) dividing nucleologenesis in four steps: compact nucleolar precursor body (NPB), monovacuolated NPB, NPB containing secondary vacuoles and fully reticulated nucleolus. These different features of early bovine embryo nucleologenesis were mainly observed during the eight-cell stage. In the first step of nucleolar development, the association of compact NPB with DNA structures was observed. DNA was also labelled in some small secondary vacuoles appearing during the third developmental step. From the second step onward, the labelling of protein C23 was observed in the compact fibrillar network of the NPB. Protein B23 started to be labelled in the compact fibrillar mass at the third step. RNA labelling was also observed for the first time in NPB containing secondary vacuoles. Labelled RNA was located in the peripheral region of compact fibrillar mass as well as along the border of the vacuoles. In the reticulated nucleolus, the dense fibrillar component was found to contain both proteins and RNA.

Developmentally regulated markers of in vitro-produced preimplantation bovine embryos

Expression of various developmentally regulated markers was screened throughout the preimplantation stages of in vitro-derived bovine embryos. This was done by investigating the distribution of several nuclear, cytoplasmic and extracellular proteins by means of immunofluorescence microscopy. While lamin B appeared as a constitutive component of nuclei of all preimplantation stages, lamins A/C had a stage-related distribution. The early cleavage stage nuclei contained lamins A/C which generally disappeared in the following stages, with the possible exception of a few positive nuclei in the morula and early blastocyst stage. In the expanded blastocyst stage the nuclei of trophectoderm cells became positive while no positivity was observed in the inner cell mass cells. Starting from day 6, the appearance and/or polarised distribution of various cytoskeletal and cytoskeleton-related components such as F-actin, alpha-catenin and E-cadherin gave an insight into the timing of events related to compaction of bovine embryos. Compaction was correlated with the first differentiation event, i.e. the formation of trophectoderm; this is the first embryonic epithelium, characterised by cytokeratins and desmoplakin. Extracellular fibronectin was first detected in the early blastocyst stage shortly before the morphological differentiation of primitive endoderm, and in the later stages it was localised at the interface between trophectoderm and extraembryonic endoderm. Laminin and collagen IV were expressed by the endoderm cells and contributed to the extracellular matrix underlying the trophectoderm. This study is a first attempt to characterise the cells of in vitro-derived bovine embryos valid for cell line derivation.

Influence of culture system and oxygen tension on the development of ovine zygotes matured and fertilized in vitro

The development and quality of ovine zygotes matured and fertilized in vitro were compared after coculture with oviductal cells (CZB-199 system) and culture in synthetic oviduct fluid medium without cells (SOF system). The effect of two oxygen concentrations (5% and 20%) on the development of ovine zygotes in SOF medium was also studied. More ovine zygotes reached the blastocyst stage when culture in SOF medium was performed in 5% O2 rather than 20% O2. A greater number of blastocysts was obtained after culture in the SOF system than coculture in the CZB-199 system. Proportions of grade I (excellent), II (good), III (fair) and IV (poor) blastocysts did not differ significantly between the SOF and CZB-199 systems. Histological examination of hatched blastocysts revealed a superiority of the SOF system for the following: a greater number of total and trophoblastic cells in grade I and II blastocysts; more endodermic cells in grade I blastocysts, higher mitotic index in the inner cell mass of grade II blastocysts and in total and trophoblastic cells of grade I, II and III blastocysts; more grade III blastocysts with mitosis in the inner cell mass; and a lower pyknotic index in the inner cell mass of grade I, II and III blastocysts. Culture in the SOF system improved the rate and quality of blastocysts in comparison with the CZB-199 system. Furthermore, culture in SOF medium with 5% O2 provided more blastocysts than culture in the presence of 20% O2.

Transcriptional activity and nucleolar ultrastructure of embryonic rabbit nuclei after transplantation to enucleated oocytes

Changes in the level of transcriptional activity in 32-cell stage morula nuclei were studied after blastomere electrofusion to enucleated oocytes. Nuclear transplant recipients were pulse labelled with 3H-uridine during cultivation in vitro, embryos were then fixed and processed for autoradiography and electron microscopy. Transcriptional activity substantially decreased after 4.5 hr and was completely inhibited at last 15 hr after fusion. Transcription resumed thereafter in two-cell stage embryos and could be detected in both nuclei from 70% of the embryos analyzed. Transcription activity rapidly increased at the eight 16-cell stages, reaching the level typical for 32-cell stage nuclei used for the transfer. Changes in nucleolar ultrastructure after the nuclear transfer reflected the inhibition and subsequent reactivation of rRNA transcription. Nucleoli of 32-cell embryos had a typical structure of active nucleoli; many fibrillar centers surrounded and interconnected by threads of the dense fibrillar component and embedded in the granular component. Six hours following nuclear transplantation, these nucleoli underwent drastic changes including loss of granular material, collapse of nucleolar structure, and segregation of nucleolar components. Following the first cleavage, segregated fibrillar components of nucleoli manifested a complete inhibition of nucleolar transcription. Ribosomal RNA transcription was restored at the eight-cell stage and the sequence of ultrastructural changes was similar to that of the normal development. However, at the 32-cell stage, excessive extrusion of pre-ribosomal particles in the cytoplasm occurred, suggesting a possible alteration in regulating mechanisms of ribosome delivery. These results show that after fusion with enucleated metaphase II cytoplasm and subsequent activation, transcription is inhibited in donor embryonic nuclei and progressively increases again during cleavage; almost as in normal embryos. Migration of ribosomes into cytoplasm appears more intense in 32-cell stage reconstituted embryos but this does not seem to inhibit blastocyst building.

Isolation and characterization of a feeder-dependent, porcine trophectoderm cell line obtained from a 9-day blastocyst

We have established in culture a feeder-dependent cell line, termed TE1, from a 9 day, pre-implantation, porcine embryo. TE1 cells were observed by light and electron microscopy, and characterized by immunocytochemistry: the morphology, cytology and ultrastructure of this cell line are described. The cells display epithelial characteristics, as revealed using immunofluorescence microscopy with antibody against cytokeratins of simple epithelia, but not with antibody against vimentin. The cells demonstrate many morphological and cytochemical features in common with trophectoderm of the intact porcine blastocyst. For example, TE1 cells are polarized and possess tight junctions at their borders, similar to those found in trophectoderm of the pre-implantation embryo. Moreover, TE1 cells label positively for the porcine trophectoderm-specific monoclonal antibody, SN1/38. Thus, by several important criteria TE1 is deduced to be a porcine trophectoderm cell line.

F-actin is involved in control of bovine cumulus expansion

Previously, we showed that the gonadotropin-induced expansion of bovine cumulus oophorus occurs concomitantly with the rearrangement of microfilaments (MFs) inside cumulus cell cytoplasm (Sutovský et al., 1993: Biol Reprod 49:1277-1287; Sutovský et al., 1994: Reprod Nutr Dev 34:415-425) and that cumulus expansion in cattle is accompanied by the increased expression of extracellular matrix (ECM) glycoproteins laminin and type IV collagen as well as of their actin-linked membrane receptors, integrin subunits alpha-6 and beta-1 (Sutovský and Motlík: 1994). The present study was undertaken to determine the spatial and temporal relationship between cytoskeletal rearrangement and ECM synthesis during cumulus expansion. Using electron microscopy and confocal (LSCM) and conventional fluorescence microscopy, we compared the expression of the above integrins and ECM proteins and the rearrangement of cytoskeleton in the gonadotropin-stimulated bovine oocyte cumulus complexes (OCCs) with those exposed to gonadotropin stimulation and to ECM synthesis inhibitor 6-diazo-5-oxo-L-norleucin (DON), or MF-disorganizing drug cytochalasin B (CB). In control OCCs, the 24-hr culture in the presence of follicle stimulating hormone/luteinizing hormone (FSH/LH) caused the expansion of cumuli oophori and an extensive rearrangement of MFs in the cytoplasm of cumulus cells. Concomitantly, we observed an increased deposition of laminin and type IV collagen in the intercellular spaces among cumulus cells. The redistribution of microtubules (MTs), intermediate filaments (IFs), and integrin chains alpha-6 and beta-1 also occurred at this time. The addition of 20 micrograms/ml of CB prevented cumulus expansion and accumulation of laminin and type IV collagen in the OCCs. Moreover, cytochalasin treatment blocked the redistribution of MTs and IFs, and caused the disorganization of MFs and dispersion of integrins in cumulus cells. In contrast, the distribution of integrins and cytoskeletal elements was not affected when we blocked cumulus expansion and ECM protein accumulation by DON. These data suggest that F-actin acts upstream of ECM synthesis in the cascade of events leading to the expansion of bovine cumulus ooophorus.

Isolation and characterization of permanent cell lines from inner cell mass cells of bovine blastocysts

Inner cell masses (ICM) from in vitro produced day 8 or 9 bovine blastocysts were isolated by immunosurgery and cultured under different conditions in order to establish which of two feeder cell types and culture media were most efficient in supporting attachment and outgrowth of the bovine ICM cells. The efficiency of attachment and outgrowth of the ICM cells could be markedly improved when STO feeder cells were used instead of bovine uterus epithelial cells, and by using charcoal-stripped serum instead of normal serum to supplement the culture medium. More than 20 stable cell lines were obtained. Some of these lines were examined by immunofluorescence for developmentally regulated markers. From these results we conclude that the cell lines resemble epithelial cells, rather than pluripotent ICM cells. The developmental potential of cells of one of the lines was tested in the nuclear transfer assay. The cell line could support the initial development of enucleated oocytes, but none of the reconstructed embryos passed the eight-cell block.

Localization of fibrillarin and nucleolin in nucleoli of mouse preimplantation embryos

The localization of fibrillarin and nucleolin in the nuclei of mouse two-cell, four-cell, and eight-cell embryos has been studied using immunofluorescent staining with specific antibodies. In all of these cleavage stages, both antigens were associated exclusively with the peripheral region of the nucleolus precursor bodies (NPBs). The original speckled fluorescent staining pattern in the early two-cell stage was progressively changed into a continuous fluorescent-positive layer localized in the cortex of the NPBs in the four-cell embryos. The compact central area of NPBs was never stained. Both proteins were colocalized in the same substructures of developing nucleoli. In order to analyze the interaction of chromatin with NPBs, DNA structures were specifically immunolabelled. At the time of resumption of nucleolar transcription (in the two-cell mouse embryo), DNA was detected at the periphery of, but not penetrating into, NPBs. Our results confirm the view that the cortical region of NPBs could represent a nucleolonemal area involved in the resumption of nucleolar transcription in the early mouse embryo.

Cellular evaluation of bovine nuclear transfer embryos developed in vitro

Cloned blastocysts developed in vitro for 7 d had a mean number of cells (82.86 +/- 5.35) as evaluated by nuclei counting in serial optical sections using confocal microscopy, after staining with propidium iodide. This number was not significantly different from that of control IVF embryos cultured under the same conditions during the same period (mean = 88.89 +/- 7.53). Semi-thin sections revealed that most of the blastocysts had an inner cell mass (10/12) and a blastocoele. Under transmission electron microscopy, the trophectoderm appeared well differentiated as a polarized epithelium with apical microvilli and lateral junctions including desmosomes with bound intermediate filaments. The cytoplasm sometimes contained immature mitochondria or a large number of residual bodies. About half of the blastocysts examined had a large amount of cellular debris in the perivitelline space or inside the blastocoele cavity. The cloned blastocysts were also able to hatch in vitro by day 8 and SEM indicated a normal morphology of the trophectoderm cells with numerous apical microvilli. The high number of excluded or degenerating cells found in some embryos may partially explain early embryonic mortality that follows transfer. However, these observations do not give a clear explanation for the high incidence of fetal losses.

Microfilaments, microtubules and intermediate filaments fulfil differential roles during gonadotropin-induced expansion of bovine cumulus oophorus

The relationship between cytoskeleton and morphology of cumulus granulosa cells in expanding bovine oocyte-cumulus complexes (OCCs) cultured in vitro has been investigated by the means of indirect immunofluorescence and transmission electron microscopy. The round-shaped cells in unstimulated control OCCs displayed a homogeneous distribution of cytoskeletal networks and cytoplasmic organelles. Luteinizing hormone (LH) stimulation caused the redistribution of microfilaments (MFs), accelerated the development of Golgi apparatus, and led to the generation of lipid droplets in cumulus cells. These changes culminated in the elongation and polarization of cumulus cells and in the extension of the cytoplasmic networks of microtubules (MTs) and intermediate filaments (IFs) into the newly formed cytoplasmic projections. The culture of OCCs in the presence of microfilament disruptor cytochalasin B prevented cumulus expansion, formation of cellular projections and cell elongation and suppressed the development of the Golgi apparatus. On the contrary, cytochalasin had no effect on the abundance and distribution of lipid droplets and on the integrity of IFs and MTs. The present data support the hypothesis that the response of cumulus granulosa cells to LH is partially mediated by F-actin.

Dynamic changes of gap junctions and cytoskeleton during in vitro culture of cattle oocyte cumulus complexes

Changes in cell-to-cell contact and distribution of cytoskeletal components were investigated during in vitro culture of cattle oocyte cumulus complexes (OCC). Freeze-fracture analysis (FF), microinjections of the fluorescent dye Lucifer Yellow (LY), immunofluorescence, and ultrastructural immunocytochemistry were used. The cumulus cells (CC) remained in close contact via gap junctions (GJ) constituted of connexin43 (Cx43) during the entire culture time. Whereas the GJ decreased in diameter after 24 h of culture, their number was still substantially great at that time. The Cx43-positive GJ, localized between corona radiata cell projections and oolemma, disappeared after 6 h of culture. Concomitantly, the OCC lost the ability to transfer LY from cumulus to oocyte, and connexin32 (Cx32) became detectable in the oocytes. Both the changes in corona-oocyte coupling and cumulus expansion were preceded by the redistribution of F-actin in cytoplasm of CC. These data indicate that functional GJ linked the CC until the second meiotic arrest. However, the removal of Cx43-positive GJ interconnecting cytoplasmic projections of corona radiata cells with the oocyte was temporally correlated with germinal vesicle breakdown. The present results suggest the pivotal role of the cytoskeleton (F-actin) in cumulus expansion.

The cytoskeleton and associated proteins during cleavage, compaction and blastocyst differentiation in the pig

The organization of the cytoskeleton during early pig embryogenesis was investigated by using fluorescence and electron microscopy. The early morphogenesis of the pig embryo differed from that of the mouse, the standard model of the early mammalian development. In the pig, both compaction and polarization were gradual, and definitive polarization of cell surface microville occurred first shortly before blastocyst formation; the compaction and polarization of the mouse embryo are completed as early as at the 8 cell stage. Furthermore, the pig morula undergoes cycles of compaction and decompaction throughout its development. Distinct changes in the distribution of actin and the actin-associated proteins alpha-fodrin, vinculin and E-cadherin coincided with these events. In the pig, all these molecules were evenly distributed at all aspects of the blastomeres during early cleavage and then gradually accumulated in regions of intercellular contacts toward the blastocyst stage; microfilaments in trophectoderm cells formed a cortical meshwork associated with apical microvilli and adherent junctions (zonula adherens). In the mouse, the corresponding changes occur earlier, at the 8 cell stage. Microtubules formed a network-like cortical layer beneath the microvilli at the free outer surfaces of pig blastomeres. Cytokeratin bundles were not observed until the early blastocyst, where they characteristically associated with newly formed desmosomes. In both species a close correlation between morphologically defined developmental stages and the organization of the cytoskeleton: actin and actin-associated proteins are involved in polarization and compaction, whereas the appearance of intermediate filament bundles coincides with the building of the first epithelium, the trophectoderm; it is in the timing of events that a contrast between species is observed.

Onset of RNA synthesis and poly (A) content of early rabbit embryos. Comparison with sheep

RNA synthesis in 2-32 cell embryos, as assessed by alpha-amanitin-sensitive 3H-uridine incorporation, was first detectable in 4-cell stage rabbit and 8-cell stage sheep embryos. In the rabbit, uridine incorporation was detectable at the 2-cell stage but was unaltered by alpha-amanitin, indicating synthesis of non-polymerase II-dependent RNA species. Initiation of mRNA synthesis as determined by in situ hybridization with 3H-poly (U) probe was first detectable in late 2-cell stage rabbit and 4-cell stage sheep embryos. In the rabbit embryos, nuclear labelling increased from the late 2-cell stage to the 16-cell stage, following a pattern similar to that of 3H-uridine incorporation. In contrast, the intensity of cytoplasmic labelling decreased from the 1- to the 8-cell stage and then increased up to the 32-cell stage. In sheep embryos, nuclear labelling by the poly (U) probe increased from the 4- to the 16-cell stage. It is concluded that initiation of transcription of the embryonic genome (mRNA) can be detected via the current methods used at the 4-cell stage in the rabbit and the 8-cell stage in the sheep.

Distribution, morphology and epithelial interactions of bovine spermatozoa in the oviduct before and after ovulation: a scanning electron microscope study

In cows undergoing spontaneous oestrous cycles and mated during the first 6 hours of oestrus, the distribution of spermatozoa in the oviduct isthmus and changes in their surface membranes and neighbouring epithelium have been examined shortly before and after ovulation. In agreement with previous histological studies, relatively few spermatozoa were detected in the oviduct lumen: most were located in the caudal isthmus before ovulation, frequently among folds and in the presence of a viscous secretion. A majority of spermatozoa in this region showed strands and droplets of secretory material distributed over the anterior portion of an intact head before ovulation, whereas distribution of material over the post-nuclear cap of spermatozoa close to vesiculation or already acrosome-reacted was characteristic of the post-ovulatory situation. These changes in sperm head membranes were viewed as an expression of the completion of capacitation, and seemingly permit microvillous engagement with the rostral tip of the head. In conjunction with a narrow lumen and viscous secretions in the caudal isthmus, microvilli may thus serve to regulate periovulatory sperm progression towards the site of fertilisation, and be the basis of intermittent phases of adhesion to the oviduct epithelium as seen by phase-contrast microscopy. Although cilia do not similarly engage the heads of bull spermatozoa (cf. boar spermatozoa), they may act to regulate progression of capacitated spermatozoa by contacting the principal piece of the flagellum. In the light of these observations, changes in the molecular composition of sperm surface domains during the process of capacitation in vivo now require specific definition.

Nucleologenesis and the onset of transcription in the eight-cell bovine embryo: fine-structural autoradiographic study

Eight-cell cow embryos were isolated and cultured in vitro in a medium enriched with 200 microCi of [5-3H]uridine for 20 min. Epon ultrathin sections of the embryos were investigated for the nucleolar morphology and for the appearance and localization of the sites of [5-3H]uridine incorporation by means of electron microscopic autoradiography. In addition to this, a general pattern of replicated embryonal DNA distribution was revealed by [methyl-3H]thymidine incorporation and light microscopic autoradiography. The essential phases of the transformation of the small nucleolus precursor body (NPB) into a vast, functionally fully active nucleolus, characterized by typical nucleolar substructural components, are taking place within the eight-cell stage. This process differed in its morphology from the nucleologenetic process in early embryogenesis of other mammals, especially of that in the mouse. The first sign of NPB transformation was the appearance of a large central vacuole followed later on by perinucleolar chromatin penetration into NPB, documented by both morphology and [3H]thymidine autoradiography. In some cases, concentration of dense fibrillar material forming clumps or stalks was seen in the central vacuole. The following rapid nucleolar development was characterized by the formation of secondary vacuoles concomitant with the onset of [5-3H]uridine incorporation into the dense fibrillar component and with the appearance of the first granules in the otherwise fibrillar structure of the nucleolus. During the late eight-cell stage, the still-rounded nucleolus developed features of a reticulated nucleolus known from somatic cells intensively synthesizing rRNA: a dense fibrillar component with associated labeling encircling fibrillar centers and a well-developed granular component. The labeled dense fibrillar component was observed mostly in the central area of the nucleolus; early embryonic NPB dense fibrous material not involved in transcription was disappearing rapidly. At the transition to the 16-cell stage the nucleoli lost their rounded shape because of the accumulation of a large amount of granular component, and they occupied a considerable part of the nucleus. In conclusion, the appearance of the nucleolar vacuole in eight-cell cow embryo is the starting point for following morphogenetic events linked with the onset of transcription.

Fusion of mammalian oocytes: SEM observations of surface changes

Mouse oocytes at the germinal vesicle (GV) stage were fused with maturing oocytes in which GVs were no longer visible. The fused cells were fixed at different time-intervals after the initiation of fusion and prepared for scanning electron microscope (SEM) observation. Concomitantly, some fused cells were prepared for light microscope evaluation. Our SEM observations showed no significant differences in surface morphology between immature and maturing oocytes. However, immediately after fusion was initiated, dramatic changes occurred on the surface of the maturing oocytes. The microvilli were shortened or disappeared locally and the plasma membrane was deeply ruffled. One hour after fusion, when the giant cells were nearly spherical, the microvilli reappeared and the ruffling gradually disappeared. In some areas, the microvilli were extremely long. Three hours after fusion, the fused cells were perfectly round and their surfaces were generally covered with microvilli of equal length. No further ruffling was observed. It is suggested that cytoplasmic mechanisms regulate the surface morphology of the oocytes during fusion.

Does autocatalytic amplification of maturation-promoting factor (MPF) exist in mammalian oocytes?

The method of polyethylene-glycol-induced fusion of mammalian oocytes was applied to study maturation-promoting factor (MPF) activity. After homologous fusions of one maturing--late diakinesis (LD), metaphase I (MI)--pig or mouse oocyte to one, two, or three immature-germinal vesicle (GV)--oocytes, giant cells were cultured in control or cycloheximide supplemented medium for 3 hours. The occurrence of germinal vesicle breakdown (GVBD) and premature chromosome condensation (PCC) served as a control of MPF activity. In giant cells composed of one maturing and one, two or three immature oocytes, GVBD and PCC were observed in all cases after cultivation in the control medium. In the presence of cycloheximide, the completion of GVBD and PCC remained high when one maturing and one immature oocyte were fused (83.7% and 95.7% of GVBD in pig and mouse, respectively). However, in giant cells composed of one maturing and up to three immature oocytes, all GVs were broken down only occasionally (4.8% and 11.7% in pig and mouse, respectively). These results suggest that in pig and mouse oocytes MPF does not amplify autocatalytically, but requires active protein synthesis for its production.

Ultrastructural localization of labeled acrosomal glycoproteins during in vivo fertilization in the rabbit

Rabbit spermatozoa were labeled predominantly in their acrosomal glycoproteins by 1-3H-glucosamine during spermiogenesis. Ova fertilized in vivo by spermatozoa labeled 22 days earlier were analyzed by fine-structure autoradiography for the localization of the label. The latter was found associated with 1) the fused membranes of the acrosomal cap remaining on the zona pellucida surface, 2) the material released on the zona surface after the acrosome reaction and possibly detectable after tannic acid fixation, 3) the equatorial segment of the sperm head and the preequatorial swellings, and 4) other sperm components, eg, the sperm tail. No labeling, on the other hand, was detected on the denuded leading edge of spermatozoa found either in the penetration slit or in the perivitelline space. Our observations suggest the involvement of acrosomal glycoproteins in different mechanisms of sperm/zona pellucida interaction but are not in favor of a major role of (enzymatic) glycoproteins bound to the inner acrosomal membrane during the penetration of the zona pellucida.

Pre- and peri-ovulatory distribution of viable spermatozoa in the pig oviduct: a scanning electron microscope study

Using sexually mature animals, the distribution of spermatozoa has been examined at the utero-tubal junction and in the distal and proximal portions of the oviduct isthmus. Mating occurred during early oestrus and, with one exception, specimens were prepared shortly before or after ovulation. Distinct reservoirs of spermatozoa were identified in furrows between the terminal folds of the isthmus, and particularly within the troughs and transverse ridges of this region. The density of spermatozoa diminished steeply from the utero-tubal junction towards the isthmus, especially in the pre-ovulatory specimens. The membranes of most spermatozoa in the isthmus were intact up to the time of ovulation, suggesting that the acrosome reaction is a peri- or post-ovulatory event. Whilst the flagella of spermatozoa in the reservoirs were usually straight or only slightly curved, those on the surface of the epithelial folds were undulating (S-shaped). Specific microenvironments may therefore exist in the distal portion of the isthmus to regulate sperm motility; droplets of secretion were a notable feature in this region. In specimens prepared 24 hr after ovulation, spermatozoa were almost absent from the utero-tubal junction and isthmus. However, denuded eggs were observed in the proximal portion of the isthmus in this animal, and they had spermatozoa associated with the zona pellucida. Arguments are presented for a peri-ovulatory endocrine regulation of sperm redistribution and capacitation.

Distribution of sterols and anionic lipids in human sperm plasma membrane: effects of in vitro capacitation

Filipin, a membrane beta-hydroxysterol probe, and polymyxin B (PXB), a probe for anionic lipids, were used to study human sperm plasma membrane (PM) with particular reference to changes induced by capacitation in vitro. In washed but noncapacitated spermatozoa the density of filipin/sterol complexes (FSC) was uniformly high in the PM overlying the acrosome, without any differences between its anterior and equatorial regions. The postacrosomal region was poor in FSC. The exclusion of FSC from small areas of the PM covering the two acrosomal regions and reduction of their number in the postacrosomal region were the main changes induced by sperm capacitation. Unlike filipin, PXB produced a capacitation-independent reaction pattern characterized by a high reactivity of the PM covering the anterior portion of the acrosome, probably conferring to this region its potential fusigenicity temporarily antagonized by the elevated sterol content. Only an exceptional and slight PXB binding was seen in the nonfusigenic equatorial and postacrosomal regions.

Membrane fusion events in the Ca2+/ionophore-induced acrosome reaction of ram spermatozoa

An acrosome reaction was induced in ejaculated ram spermatozoa by treatment with calcium and the ionophore A23187. Samples were fixed at different times after initiation of induction, and the morphological changes within the head membranes that took place as exocytosis occurred were studied in freeze-fracture replicas. Reacted acrosomes appeared in individual spermatozoa within the calcium/ionophore-treated population at different times after the start of treatment; the first cells had reacted by 10 min, whereas some took more than 40 min to react. No changes were observed in control populations. An early effect of treatment (seen in most cells within 10 min) was the appearance of particle-free ‘clearings’ in the plasma membrane over the entire acrosomal region, with aggregation of intramembranous particles between and around these ‘clearings’. At the same time, there was an increase in the number of large particles (greater than or equal to 10 nm) within the plasma membrane over the ‘lunula’ of the equatorial segment and the anterior part of the post-acrosomal region. Fusion of the plasma and outer acrosomal membranes began in a limited area at the border between the anterior and equatorial segments of the acrosome. It then spread, following arborescent pathways, sideways along this border and forwards towards the apex of the head. This labyrinthic propagation resulted in an ‘acrosomal cap’ increasingly fenestrated towards its posterior margin. Fusion propagation over the equatorial segment was inhibited, apparently as a result of the highly ordered structure of the membranes in this region.

Ultrastructural study of the interactions and fusion of ram spermatozoa with zona-free hamster oocytes

The interaction of preincubated ram sperm with zona-free hamster oocytes was studied by scanning and transmission electron microscopy. The behaviour of the sperm cells was quite different, depending on whether the acrosomal reaction had taken place or not. The apical ridge of intact spermatozoa contacted the oocyte surface, and egg microvilli spread onto the anterior segment but no fusion ensued. When the acrosomal cap was fenestrated, microvilli were also found on its surface but were then spread over the surface of the postacrosomal region and the equatorial segment of the sperm head lying flat on the egg surface; fusion with the oocyte occurred in the equatorial segment and extended to the postacrosomal region. Contacts between the microvilli and the inner acrosomal membrane were infrequent and no fusion occurred in the anterior segment. These observations confirm that local changes in the adhesiveness and fusibility of the sperm plasma surface occurred during the acrosome reaction.

Autoradiography of 3H-uridine incorporation in the normal early blastocysts of cattle

RNA synthesis in morphologically normal early bovine blastocysts collected 7 days after insemination was investigated using fine-structure autoradiography after 3H-uridine incorporation. The level of autoradiographic labelling is proposed as a criterion for assessing metabolic activity in the individual cells of the blastocyst. There was a detectable difference between the cells of the trophoblast and those of the inner cell mass (higher labelling), indicating a divergence of metabolic patterns according to blastomere differentiation. The occasional absence of nuclear labelling was correlated with cell degeneration. A low nuclear labelling was observed mainly in cells sequestered in the subzonal space or in the blastocoele cavity, respectively. Estimation of RNA synthesis in different blastomeres by fine structure autoradiography opens the way to a better interpretation of the relationship between morphology and metabolism during the development of early cow embryos.

Changes in intercellular coupling between pig oocytes and cumulus cells during maturation in vivo and in vitro

Cumulus expansion and cumulus cell-oocyte coupling during in-vivo and in-vitro maturation of pig oocytes were studied by measuring [3H]uridine uptake. In vivo, cumulus expansion started before germinal vesicle breakdown (GVBD) (16 h versus 20 h after hCG) but no significant change occurred in the coupling index until 32 h after hCG. Intercellular coupling was decreasing at 32 h after hCG in oocytes at anaphase I and telophase I. Complete uncoupling was closely correlated with corona radiata expansion. In vitro, partial uncoupling was observed in oocyte-cumulus cell complexes from prepubertal and PMSG-stimulated gilts cultured for 16 and 32 h, respectively. The addition of FSH caused cumulus expansion, and the functional coupling between the cumulus cells and the oocyte was maintained up to at least 16 h of culture in complexes from prepubertal gilts. We conclude that, under our conditions, neither hormone-free nor FSH-supplemented medium ensured the same [3H]uridine uptake and uncoupling kinetics as during in-vivo maturation.

Cumulus oophorus mucification during resumption of meiosis in the pig. A scanning electron microscope study

The process of cumulus mucification in pig preovulatory follicles was examined by scanning electron microscopy. The localization of extracellular material and changes in the granulosa cell surface were observed at 0, 16, 20 and 40 h after hCG injection. At 0 h the pig oocyte cumulus complex was closely attached to the parietal layer of granulosa cells. Cumulus and parietal granulosa cells had microvilli and cytoplasmic projections connecting neighbouring cells. The network of extracellular amorphous material was observed for the first time at 16 h after hCG around the cells that formed a stalk between the parietal granulosa and the cumulus oophorus. At 20 h after hCG, the intercellular matrix was thicker and extended to almost all the cumulus oophorus surface; when visible, cells were often covered by blebs and ruffling membranes. All oocytes examined by light microscopy at 16 and 20 h after hCG were at the germinal vesicle stage with condensing bivalents. Therefore, it was concluded that oocyte nuclear maturation started at the same time that a mucified peduncle was forming between the cumulus oophorus and the parietal granulosa. Shortly before ovulation (40 h after hCG) the matrix material filled all intercellular spaces and mucification had extended to the corona cell layer and the zona pellucida surface.

Experimental studies on the elongation of the ewe blastocyst

After the zona is shed, the ewe blastocyst increases rapidly in diameter and length. The aim of the present study was to examine the control of trophoblast growth. Twelve-day old ovine blastocysts, cut into pieces and cultured in vitro for 24 h, gave rise to structures called trophoblastic vesicles (blastocysts without the embryonic disc). Such trophoblastic vesicles (TV), cultured at least 5 to 10 days or more in vitro, were able to survive. However, they did not increase in length and only some of them began to form small buds. In contrast, after they were transferred surgically into the uterine horn ipsilateral to the corpus luteum on Day 12 of the oestrous cycle, these TV were elongated in 5 out of 7 recipient ewes slaughtered on Day 17. The structure of the TV was observed by scanning electron microscopy before and after in vitro elongation and then compared with that of control blastocysts which had been cultured or not. This study demonstrates that trophoblast elongation does not depend necessarily on the presence of the embryo proper, but can occur in TV composed only of the trophectoderm and the extraembryonic endoderm. The results also suggest that some unknown uterine factor(s) is involved in the development of trophoblastic tissue.

Autoradiographic detection of the earliest stage of [3H]-uridine incorporation into the cow embryo

Cow embryos, obtained from superovulated heifers on days 3 and 4 after oestrus, were cultured for 20 min in Ménézo's complete culture medium (B2), enriched with 200 microCi/ml of 5-[3H]-uridine. Semi-thin Epon sections of this material were investigated by autoradiography for sites of RNA synthesis. It was found that 5-[3H]-uridine was incorporated into the nucleoplasm and nucleoli only at the end of the 8-cell stage. This suggested that synthesis of hnRNA and rRNA occurred from this stage onwards. Ultrastructural studies were performed on these embryos as well as on other non-incubated 4-cell embryos recovered on day 2. The transformation of dense fibrillar primary nucleoli into functional reticulated nucleoli appeared sooner in the development of cow embryos than in other mammalian species hitherto studied and took place generally during the 8-cell stage. An unusual step in this transformation was represented by the development of a single vacuole in nucleoli at the beginning of this stage (day 3 post-oestrus).

Sperm surface changes during the acrosome reaction as observed by freeze-fracture

The mammalian acrosome reaction is an exocytotic process that can be analyzed by the technique of freeze-fracture; only sperm cells capacitated in vitro or treated to elicit the acrosome reaction in vitro have been studied, and all pictures published are from material fixed before freezing. All the authors point out the appearance of particle-free areas in the plasma membrane of the acrosomal region during capacitation and before any fusion. This is interpreted as an increase in membrane fluidity as suggested by studies on membrane lipid composition in guinea-pig sperm. We have recently described the induced acrosome reaction in ram spermatozoa. Fusion starts at the limit of the anterior and equatorial segments and progresses forward in the anterior segment along ramified paths, resulting in a fenestration gradient of the acrosomal cap. Fusion propagation may be controlled by fluidity increase in the plasma membrane of the anterior segment, and it is probably inhibited in the equatorial segment by the ordered structure of the acrosomal membrane.

Some factors influencing the interaction of ram spermatozoa with zona-free hamster eggs

Variability in the interaction of ram spermatozoa with zona-free hamster eggs was recorded not only amongst individual males but also between the first and second ejaculates of the same male collected 30 min apart. Fusion ability also differed according to the conditions of gamete mixing. This ability decreased after in-vitro storage of undiluted ejaculates at room temperature but lasted for 48-192 h. The kinetics of sperm-egg fusion during the time of gamete incubation varied not only with the time of sperm storage in vitro but also with the ejaculate. When the semen was frozen, the ability of the spermatozoa to fuse was markedly reduced.

Binding of secreted glycoproteins to spermatozoa in the mammalian epididymis: a fine-structure autoradiographic study

Mouse and guinea pig epididymal tissues have been investigated by light and electron microscopic autoradiography after long intervals ranging from 24 h to 5 days postinjection (p.i.) of the glycoprotein precursors, L-fucose-6-3H or D-glucosamine-1-3H. Using modified fixations to enhance glycoprotein preservation in situ, we found intense labelling of luminal contents in at least some of the epididymal segments after all the intervals investigated. At 24 h p.i., the label in guinea pig was associated with spermatozoa during remodelling of the acrosome in segment II, and at 3 days p.i., radioactivity was trapped within sperm head associations ("rouleaux") in segment IV of the epididymis. At this time, similar rouleau labelling extended from segment IV to segment VIII. In mouse, the luminal contents of the cauda epididymis were still intensely labelled at 5 days p.i.; analysis of the electron microscopic autoradiograms showed that relative grain concentration over the spermatozoa was twice that of the epididymal plasma. This concentration was especially elevated in the region of the sperm head. These findings taken together were interpreted as the binding of secreted epididymal glycoproteins to spermatozoa during sperm transit through the epididymis. In contrast to luminal contents, the labelling of the epididymal epithelium was generally lower, except on the clear cells which showed more pronounced labelling than the neighboring principal cells in mouse cauda epididymis at 5 days p.i. This label probably originated from the resorption of luminal glycoproteins.

Dynamics of zona pellucida formation by the mouse oocyte. An autoradiographic study

The dynamics of the synthesis of the mouse oocyte zona pellucida was studied using light microscope autoradiography after intrabursal injection of (3H) -fucose. Zona accretion occurred continuously from the inside, demonstrating that the oocyte itself elaborated all the raw material of the zona. The duration of zona synthesis corresponded to that of the oocyte growth phase. Zona secretion stopped one week before ovulation and there was no renewal of its material.

Studies on acrosome labelling of mammalian spermatozoa by radioactive sugars

The localization of glycoprotein synthesis and storage was studied during acrosome formation in guinea-pig using fine-structure autoradiography after (3H)-fucose incorporation. Three days after (3H)-fucose injection, labelling in spermatids was concentrated in the matrix of developing acrosomes, and it was evident that the fucosylation of acrosomal glycoproteins largely overshadowed the fucosylation of other spermatid glycoproteins. Acrosin labelling and its quantitative relation to labelling of other glycoproteins was examined in mature rabbit spermatozoa after incorporation of (14C)-fucose or (14C)-glucosamine during spermatogenesis. Cauda epididymis spermatozoa recovered 21 days after intratesticular application of (14C)-fucose or (14C)-glucosamine were analysed for acrosin specific labelling after acid extraction and gel filtration. In all the material examined, radioactivity was detected in the proacrosine fractions; radioactivity in purified proacrosin amounted to at least 2% of the total radioactivity in the epididymal sperm population. In addition to the peak with radioactive proacrosin, another radioactive peak in (14C)-glucosamine-labelled material was attributed to a glycoprotein intraacrosomal inhibitor of acrosin. It is concluded that (pro)acrosin (acrosin-inhibitor) complexes seem to contribute significantly to acrosomal glycoprotein labelling by radioactive sugars and that the distribution of these complexes may at least correspond to their cytochemically detectable component, acrosin. The superposition of the distribution of acrosin and of other acrosomal glycoproteins during acrosome reaction can be explained by the fact that the dispersal of most of the acrosomal content is linked to proacrosin activation.

Expression of beta 2-microglobulin on preimplantation pig embryos

The expression of beta-2 microglobulin (beta 2m), a protein associated with the histocompatibility antigens of the pig complex (SLA), was studied in preimplantation embryos between the segmentation stage and the beginning of elongation (day 12). The antigen was visualized at the ultrastructural level by immunocytochemical techniques using peroxidase or colloidal gold particles as labels. beta 2m expression appeared to parallel trophoblast differentiation. No positive reaction was obtained before the early blastocyst stage. From this stage on, labelling was observed on the apical surface of the trophectoderm cells.

Cytochemical studies of uterine and trophoblastic surface coats during blastocyst attachment in the ewe

A glycoprotein coat was demonstrated on the outer surface of both the uterine and trophoblastic cells using ruthenium red, cationized ferritin, concanavalin A-peroxidase and phosphotungstic acid in HCl. No changes were observed on the uterine epithelial surface of cyclic or pregnant animals before or during blastocyst attachment (Day 15). However, the cytochemical reactions were different on the trophoblastic cells of blastocysts at Days 13 and 15, the ruthenium red and cationized ferritin sites of reaction and the concanavalin A receptors being more homogeneously distributed on the outer surface of Day-15 trophoblast. The phosphotungstic acid staining demonstrated a glycoprotein substance between the trophoblast and the uterine epithelium in adhesion areas by Day 18. The results suggest that biochemical changes occur in the composition or distribution of the trophoblastic cell coat during the process of blastocyst attachment in the ewe.

The fate and role of macromolecules synthesized during mammalian oocyte meiotic maturation. II. - Autoradiographic topography of [3H]-fucose incorporation in pig oocytes cultured in vitro

Pig oocytes in different maturational stages--germinal vesicle (GV), metaphase I (MI) and metaphase II (MII)--were cultured in vitro with [3H]-fucose. The incorporation of the precursor was followed by LM or EM autoradiography on air-dried preparations and on semithin or thin sections. The cumulus cells connected with the oocytes at the GV stage were intensely labelled, while the labelling of the cumulus of MI and MII oocytes was lower. The cytoplasm of oocytes in the GV stage was characterized by nests of silver grains located mainly in a juxtanuclear position. The accumulation of label in the cortical region, observed in oocytes cultured with an intact cumulus, was less evident in cumulus-deprived oocytes. Lower labelling of the ooplasm, together with uniform distribution of the grains, was observed in later stages of meiosis. EM autoradiographs demonstrated the main localization, at the GV stage, of label in the Golgi apparatus and near the cell surface of oocytes and cumulus cells, as well as in the cytoplasmic processes of corona radiata cells. It is concluded that a relatively intense glycoprotein synthesis takes place in pig oocytes and cumulus cells during resumption of meiosis, at least before GV breakdown. Metabolic cooperation may occur as long as oocytes and cumulus cells keep membrane junctions.

Conceptus attachment in the ewe: an ultrastructural study

Scanning and transmission electron microscopic observations were made on trophoblast, caruncles and intercaruncular areas during the attachment of the conceptus. Three stages were determined: 1. From day 14 on, precontact was established and the conceptus appeared to be immobilized in the uterine lumen. On the centres of the caruncles which were depressed and folded the epithelial cells developed bulbous cytoplasmic protrusions. Throughout the free life of the conceptus, the trophoblast cells showed an abundant covering of microvilli. 2. On day 15, apposition occurred: most microvilli on the surface of the trophoblast disappeared. 3. Between days 16 and 18, adhesion began as a result of the interpenetration of the uterine microvilli and cytoplasmic projections of the trophoblast cells. During that stage trophoblast giant cells appeared and the uterine epithelium was turned into syncytial masses; however, it was apparently not destroyed later on. Between the caruncles, the trophoblast developed finger-like villi which invaded the lumen of the uterine glands from days 15 to 18. During their short life-time (they vanish at day 20), these trophoblastic differentiations may anchor the pre-attachment conceptus and absorb the histotrophic secretions of the glands.

Distribution of spermatozoa in the utero-tubal junction and isthmus of pigs, and their relationship with the luminal epithelium after mating: a scanning electron microscope study

The epithelial cell morphology and distribution in the utero-tubal junction and isthmus of pigs was documented by scanning electron microscopy around ovulation. In animals mated at different times before slaughter, our observations confirmed that the utero-tubal junction and posterior part of the isthmus regulate the transport of spermatozoa. The utero-tubal junction appears clearly as a form of mechanical valve strongly limiting the number of sperm cells penetrating the oviduct. The isthmus, and especially its posterior part poor in ciliated cells, is a storage place for spermatozoa which appear as though trapped in the epithelial folds. It remains to be demonstrated if they stay in such reservoirs due to the constriction of the lumen by the thick muscular wall of the duct, or to some chemotactic attraction by tubal secretions, or simply due to adhesion on the epithelium. Our study supports the hypothesis that transport of spermatozoa in the isthmus towards the site of fertilization depends in part on ciliary motion. The instant direction of propagation appears random for spermatozoa escaping from the reservoirs. Other factors such as tubal contractions probably ensure that the resultant movement is a progressive ascent.