Multicolour fluorescence in situ hybridisation (FISH) analysis of interphase nuclei in cleavage stage human embryos has highlighted a high incidence of postzygotic chromosomal mosaicism, including both aneuploid and ploidy mosaicism. Indeed, some embryos appear to have a chaotic chromosomal complement in a majority of nuclei, suggesting that cell cycle checkpoints may not operate in early cleavage. Most of these studies, however, have only analysed a limited number of chromosomes (3–5), making it difficult to distinguish FISH artefacts from true aneuploidy. We now report analysis of 11 chromosomes in five sequential hybridisations with standard combinations of two or three probes and minimal loss of hybridisation efficiency. Analysis of a series of arrested human embryos revealed a generally consistent pattern of hybridisation on which was superimposed frequent deletion of one or both chromosomes of a specific pair in two or more nuclei indicating a clonal origin and continued cleavage following chromosome loss. With a binucleate cell in a predominantly triploid XXX embryo, the two nuclei remained attached during preparation and the chaotic diploid/triphoid status of every chromosome analysed was the same for each nucleus. Furthermore, in each hybridisation the signals were distributed as a mirror-image about the plane of attachment, indicating premature decondensation during anaphase consistent with a lack of checkpoint control.

The aim of this study was to optimise porcine in vitro fertilisation (IVF) with cryopreserved semen with the exploitation of the oviduct secretion. The oocytes were cultured in NCSU37 supplemented with db-cAMP (1 mM), porcine follicular fluid (pFF; 10%), cysteine (0.1 mg/ml) and β-mercaptoethanol (25 μM) for 44 h (the first 20 h with 10 IU/ml hCG and PMSG). The oviductal epithelial cells (OEC) were cultured in TCM-199 medium (with 10% FCS, 0.2 mM pyruvate and 50 μg/ml gentamicin) for 48 h. To determine the effects of OEC and conditioned medium, oocytes were separated into five groups for the last 3 h of maturation and placed in: fresh maturation medium (controls), OEC-cNCSU with OEC in the maturation medium for 24 h; OEC-fNUSU with fresh OEC in maturation medium; cTCM with TCM-199 conditioned with OEC for 48 h; or fTCM with fresh TCM-199. Results indicate that OEC-cNCSU and OEC-fNCSU increase the number of oocytes reaching the two pronucleus (2PN) stage (p < 0.01) and decrease the polyspermy rate (p < 0.01) compared with controls. The rates are significantly lower than controls when cTCM and fTCM were used (p < 0.01). As regards blastocyst rates, an increase was observed in the OEC-cNCSU and cTCM groups (p < 0.05). For the second experiment, spermatozoa were incubated with OEC in IVF medium (mTBM medium supplemented with 0.1% BSA) without caffeine for 4 h prior to IVF. Results indicate that sperm treatment with OEC increases the 2PN rate (p < 0.01) compared with controls and reduces the polyspermy rate (p < 0.01). In conclusion, our study shows that co-incubation of OEC with both oocytes and sperm before IVF reduces polyspermy rates and improves embryo development.

In this study we examined the behaviour and role of an intra-acrosomal antigenic molecule, acrin 3, during mouse fertilisation in vitro by assessing the effect of its pertinent monoclonal antibody mMC101. Experiments were designed to assess the effect of mMC101 on sperm–zona pellucida binding, the acrosome reaction, zona pellucida penetration, sperm–egg fusion, and fertilisation in vitro. mMC101 did not affect sperm motility or primary and secondary binding to the zona pellucida, but significantly inhibited fertilisation of zona-pellucida-intact oocytes in a dose-dependent manner. In the presence of mMC101 at 100 μg/ml concentration in TYH medium, none of the oocytes developed to pronuclear stage by 5 h after co-incubation of the gametes, but the pronucleus formation rate recovered to some extent (45.3%) after 8 h, indicating a delay of early embryonic development. mMC101 also delayed and significantly suppressed zona pellucida penetration by sperm. Acrin 3 dispersed and did not remain on completely acrosome-reacted sperm. Although mMC101 did not influence the zona-pellucida-induced acrosome reaction, it significantly inhibited fertilisation when acrosome-reacted sperm in the presence of mMC101 inseminated zona-pellucida-free oocytes. However, fertilisation remained unaffected when acrosome-reacted sperm in the absence of mMC101 inseminated zona-pellucida-free oocytes even in its presence. Thus, acrin 3 appears to facilitate zona pellucida penetration and is also likely to be involved in sperm–oocyte fusion by modifying the sperm plasma membrane during the acrosome reaction.

In a previous study of mouse tetraploid[harr ]diploid chimaeric blastocysts, tetraploid cells were found to be more abundant in the trophectoderm than the inner cell mass (ICM) and more abundant in the mural trophectoderm than the polar trophectoderm. This non-random allocation of tetraploid cells to different regions of the chimaeric blastocyst may contribute to the restricted tissue distribution seen in postimplantation stage tetraploid[harr ]diploid chimaeras. However, the tetraploid and diploid embryos that were aggregated together differed in several respects: the tetraploid embryos had fewer cells and these cells were bigger and differed in ploidy. Each of these factors might underlie a non-random allocation of tetraploid cells to the chimaeric blastocyst. A combination of micromanipulation and electrofusion was used to produce two series of chimaeras that distinguished between the effects of cell size and ploidy on the allocation of cells to different tissues in chimaeric blastocysts. When aggregated cells differed in cell size but not ploidy, the derivatives of the larger cell contributed significantly more to the mural trophectoderm and polar trophectoderm than the ICM. When aggregated cells differed in ploidy but not cell size, the tetraploid cells contributed significantly more to the mural trophectoderm than the ICM. In both experiments the contributions to the polar trophectoderm tended to be intermediate between those of the mural trophectoderm and ICM. These experiments show that both the larger size and increased ploidy of tetraploid cells could have contributed to the non-random cell distribution that was observed in a previous study of tetraploid[harr ]diploid chimaeric blastocysts.

1-Methyladenine (1-MeAde) in starfish was the first compound to be identified as an oocyte maturation-inducing substance (MIS) among invertebrates in 1969 by Kanatani and co-workers. In starfish, the ripe ovary contains a huge number of fully grown oocytes of almost equal size. Each oocyte possesses a large nucleus (germinal vesicle, GV), which is arrested in late prophase of the first maturation division. The oocyte is surrounded by a single follicle layer. Such immature oocytes are not fertilisable. Resumption of meiosis in immature oocytes can be induced by 1-MeAde, and the mature oocytes thus become fertilisable (Kanatani et al., 1969; Kanatani, 1985). 1-MeAde is produced by ovarian follicle cells upon stimulation with a gonad-stimulating substance (GSS) released from the radial nerves (Fig. 1).

It has been demonstrated that GSS is a peptide hormone (Kanatani et al., 1971). The action of GSS on 1-MeAde production in follicle cells appears to be mediated by its receptor, G-proteins and adenylyl cyclase (Mita & Nagahama, 1991). These findings suggest that a G-protein coupled (seven transmembrane type) receptor is involved in GSS signal transduction, similarly to the pituitary-gonadal axis in vertebrates.

Thus, using degenerate probes derived from consensus sequences of the mammalian glycoprotein hormone (GTH and TSH) receptors, cDNA was cloned from mRNA of ovaries of Asterina pectinifera. The cDNA showed striking structural homology with members of the glycoprotein hormone receptor family in the transmembrane region, and contained a very large extracellular region. Expression was observed in isolated ovarian follicle cells. Thus, it seems likely that the glycoprotein hormone receptor (GTHR) family gene is related to GSS receptor in ovarian follicle cells. The phylogenic relatedness of the starfish GTHR was also assessed in relation to other vertebrate GTHRs. The analysis showed that the starfish gene diverged before differentiation of the gonadotropin (LH and FSH) and TSH receptors in vertebrates.

This study was carried out to examine how different combinations of pyruvate and glucose affect spontaneous meiotic maturation of cumulus-cell-enclosed mouse oocytes (CEO) to metaphase II (MII). Most experiments used an open system in which oocytes were cultured in 1 ml medium in plastic tubes. Initial experiments examined the dose response effects of pyruvate or glucose alone in the presence or absence of 2 mM glutamine. When medium lacked both pyruvate and glucose, more than 91% of the oocytes died in glutamine-free medium during 15 h of culture; viability was restored with the addition of glutamine, but only 11% of the CEO reached MII. In the absence of glutamine, 62–68% of oocytes completed maturation in 0.23–2.3 mM pyruvate, while 44–60% MII was observed in 0.55–27.8 mM glucose. The addition of glutamine to these cultures had a general suppressive effect on the completion of maturation. When glucose was added to pyruvate-containing cultures, the combination of 1 mM pyruvate/5.5 mM glucose was most effective in supporting maturation (about 90% MII), with little effect of glutamine. No further increase in maturation was observed when glucose was increased five-fold (to 27.8 mM). The positive effect of glucose was in part attributed to stimulation of glycolysis and increased production of pyruvate, since a reduced culture volume (8 μl), which allows the accumulation of secreted pyruvate, improved maturation in glucose-containing, but not pyruvate-containing, medium, and FSH, which stimulates glycolysis, increased progression to MII in glucose-containing, but not pyruvate-containing, medium. Yet these results also suggest that glucose has a beneficial effect on maturation apart from simple provision of pyruvate. The pyruvate effect was directly on the oocyte, because denuded oocytes responded more effectively than CEO to this energy substrate. The highest percentage of MII oocytes (96–97%) occurred in microdrop cultures containing glucose but lacking glutamine. These results indicate that glutamine supports oocyte viability but is not an adequate energy source for the completion of spontaneous meiotic maturation and may be detrimental. In addition, while pyruvate and glucose alone can each support meiotic progression of CEO to MII, optimal maturation requires the provision of both substrates to the culture medium when a large volume (1 ml) is used. It is concluded that careful attention to specific energy substrate supplementation and culture volume is important to optimise spontaneous meiotic maturation in vitro.

In zygotes of almost all animals, it has been believed that only the sperm centrosome acts as the mitotic spindle poles. As first proposed a century ago by Boveri (1887), this uniparental (paternal) inheritance of the centrosome must depend on the selective loss of the maternal centrosomes. To trace the fate and duplicating capacity of all the maternal centrosomes/centrioles, including those cast off into polar bodies, we used two kinds of procedures: (1) suppression of polar body (PB) extrusion and (2) transplantation of PB centro-somes into artificially activated eggs.

Gametes used in this study were from the starfish, Asterina pectinifera. Oocyte maturation was induced with 1-methyladenine (Kanatani, 1969). Suppression of PB extrusion and artificial activation were done according to Washitani-Nemoto et al. (1994). Micromanipulation was performed by the method of Saiki & Hamaguchi (1993). Behaviour of the centrosomes was examined by staining with an antibody against α-tubulin, polarisation and differential interference-contrast microscopy and transmission electron microscopy.

In starfish oocytes, no centriole duplication occurs in meiosis II, hence each pole of a meiosis II spindle is formed by the splitting of paired centrioles in the inner centrosome of a meiosis I spindle into singles. Eventually, each of a second PB (PB2) and a mature egg inherits only one centriole from a meiosis II spindle (a PB1 inherits a pair of centrioles). So, either PB2 and the mature egg inherit a single centriole (Fig. 1; cf. Sluder et al., 1989; Kato et al., 1990). When mature eggs were artificially activated with the Ca2+-ionophore A23187, a single monaster was formed.

Although the in vitro fertilisation index is a parameter commonly employed to investigate sperm functional activity, little attention has been given to the occurrence of parthenogenesis. The purpose of this study was to study at 6 h or 22 h incubation: (a) the cleavage-related events that occur in in vitro incubated mouse oocytes, in the absence (parthenogenesis) or presence of homologous spermatozoa; (b) the effect of mineral oil, commonly used in in vitro fertilisation assays; (c) the effect of piroxicam, a prostaglandin synthesis inhibitor, on the parthenogenetic rate; and (d) the influence on parthenogenesis of spontaneous loss of the cumulus oophorus coat during incubation. Under the experimental conditions employed, there was parthenogenetic activation and activation due to fertilisation. Both increased in a time-dependent manner. The mineral oil enhanced the parthenogenetic rate at 22 h incubation. However, it did not have any effect when the oocytes were inseminated. Since we can not discriminate how much of this activation was due to fertilisation and how much to parthenogenesis we must be very careful with this comparison. Piroxicam 10-8 M did not show any effect on the mouse oocyte parthenogenetic rate at neither 6 h or 22 h incubation. Our results suggest that oocyte susceptibility to spontaneous parthenogenetic activation may be modified by the presence of the cumulus and corona radiata cells. In conclusion, we consider that further rigorous studies on these influences are necessary in order to confer more reliability on the results.

This study confirms our previous data on the effects of sex hormones on mast cell number (MCN) in the testis of frog Rana esculenta. After 15 days of treatment with oestradiol (E2) MCN strongly increases, while testosterone has no effect. After 30 days only a small increase in MCN is observed. These differences could be due to the non-physiological effect of E2 over a prolonged period. We also confirmed a massive increase in MCN after 15 or 30 days of treatment with cyproterone acetate (CPA). This increase in MCN is also observed after administration of CPA with tamoxifen. Ultrastructural analysis of testis shows empty spaces with degenerating Leydig cells in the interstitial compartment and numerous germinal cells completely degenerated, probably apoptotic, in the adjacent germinal compartment. The same effects were observed in testes after treatment with only CPA. Chronic E2 treatment provokes an increase in MCN on day 2. From day 4 to 12 of the treatment, MCN decreases dramatically and many germinal tubules appear strongly disorganised. In conclusion, the present results confirm that E2 treatment induces changes in MCN and chronic E2 treatment modifies the morphology of the frog testes. In addition, blocking androgen receptors with CPA, alone or in combination with tamoxifen, causes a significant increase in MCN, confirming the involvement of androgens in mast cell proliferation and/or differentiation.

We show that in contrast to metaphase II oocytes, metaphase I oocytes cannot be activated by fusion with the zygote. Fusion of metaphase I oocytes with G2 zygotes was followed by premature chromosome condensation, with 60% of the hybrids becoming arrested at metaphase I, the remainder progressing and arresting at metaphase II. Hybrids of metaphase I oocytes and M-phase zygotes underwent accelerated maturation, but all arrested at metaphase II. In both cases the arrest could be overcome by treatment with the parthenogenetic activators ethanol and cycloheximide. We discuss these findings in relation to the possibility that the metaphase I oocyte contains cytostatic factor activity that is activated by its zygotic partner. Alternatively, the G2 zygote may provide an inhibitor of anaphase, normally never present in the metaphase I oocyte and which is absent from the M-phase zygote.

Pig oocytes at metaphase II were activated by penetration of spermatozoa in cycloheximide-free and cycloheximide-containing fertilisation media. The precise nuclear stage, and the kinetics of degradation of cyclin B1 and dephosphorylation of MAP kinase were assessed after insemination. After maturation culture, 96% of oocytes reached metaphase II. At 6 h after insemination in cycloheximide-free medium, 68% of the oocytes were activated and had progressed to anaphase II or beyond. After 8 h, 89% of the oocytes were activated: a female pronucleus had formed and the heads of penetrating spermatozoa had enlarged and changed to male pronuclei. In the cycloheximide-containing medium, activation of oocytes started earlier than in cycloheximide-free medium. After 4 h, 43% of the oocytes were activated, and the percentage increased to 97% after 6 h. Pig cyclin B1 disappeared in the oocytes at 6 h after insemination in both cycloheximide-containing and cycloheximide-free media. Pig oocytes at metaphase II contained two types of MAP kinase – ERK 1 and ERK 2 – in their active phosphorylated forms. At 8 h after insemination ERK 2 changed to the fast-migrating inactive form in the oocytes cultured in both cycloheximide-containing and cycloheximide-free media, although the shift-down was not complete. The change was delayed by 2 h after the degradation of cyclin B1 molecules. These results demonstrate that degradation of pig cyclin B1 molecules corresponds to the transition of the oocytes from metaphase II arrest to anaphase II/telophase II and was followed by MAP kinase dephosphorylation.

We have recently presented evidence that the structural integrity of the mouse sperm nuclear matrix may be necessary for the proper unpackaging of sperm DNA for participation in embryogenesis. It is likely that the sperm nuclear matrix contributes to the organisation of the sperm DNA and its disturbance can seriously damage the paternal genome or its expression. In this work, we confirm our previous data and further suggest that even very subtle changes in the sperm nuclear structure may have a significant impact on embryo development. As reported previously, dithiothreitol (DTT) in the presence of an ionic detergent, ATAB, destabilised the nuclear matrix as measured by the halo assay, and oocytes injected with these nuclei failed to develop. We also discovered that omitting the protease inhibitor PMSF from the buffers used to extract spermatozoa prevented sperm injected into oocytes from participating in development. The organisation of DNA into loop domains by the nuclear matrix in these nuclei appeared normal, as measured by the halo assay. Oocytes injected with sperm nuclei that had been washed with ATAB in the presence of phenylmethylsulphonyl fluoride (PMSF) but in the absence of DTT resulted in live births. Neither DTT treatment nor the absence of PMSF would be expected to disrupt the integrity of the paternal DNA. The data therefore suggest that even very subtle alterations in the structural proteins of the nucleus are enough to deprive sperm DNA of the ability to contribute to embryonic development.

While all ascidians (Urochordata) are hermaphroditic, some, including Halocynthia roretzi (Fuke, 1983) and Ciona intestinalis (Rosati & De Santis, 1978) are strictly self-sterile because of a self–nonself recognition system in the interaction between the sperm and the vitelline coat of the eggs. However, immature oocytes (Fuke & Numakunai, 1996) and acidic-seawater-treated mature oocytes (Morgan, 1939; Kawamura et al., 1991) are self-fertile. It is thought that a putative self–nonself recognition molecule, which is detached or modified by treatment with acidic seawater, may be attached to the vitelline coat during oocyte maturation. Although the existence of a self–nonself recognition system in the fertilisation process is well known, the molecular entity has yet to be conclusively identified. However, there have been several attempts to identify such a molecule in Ciona (Marino et al., 1999). In the present study, we have isolated and analysed a molecule which appears to be responsible for allorecognition in the interaction between sperm and eggs of the ascidian Halocynthia roretzi.

Biologicals. A solitary ascidian Halocynthia roretzi Type C was used in this study. The fertilisation experiment was carried out as described previously (Sawada et al., 1982).

Isolation and N-terminal Sequencing of Hr VC70. Vitelline coats were isolated from immature and mature oocytes of the ascidian by homogenisation and repeated washing with 5× diluted artificial seawater. The isolated vitelline coats were subjected to SDS-PAGE, followed by blotting to a PVDF membrane. The N-terminal amino acid sequence of the 70 kDa main component (HrVC70) was determined by a protein sequencer.

Studies with intact preimplantation mouse embryos and some types of chimaeric aggregates have shown that the most advanced cells are preferentially allocated to the inner cell mass (ICM) rather than the trophectoderm. Thus, differences between 4-cell and 8-cell stage embryos could contribute to the tendency for tetraploid cells to colonise the trophectoderm more readily than the ICM in 4-cell tetraploid[harr ]8 cell diploid chimaeras. The aim of the present study was to test whether 4-cell stage embryos in 4-cell diploid[harr ]8-cell diploid aggregates contributed equally to all lineages present in the E12.5 conceptus. These chimaeras were compared with those produced from standard aggregates of two whole 8-cell embryos and aggregates of half an 8-cell embryo with a whole 8-cell embryo. As expected, the overall contribution of 4-cell embryos was lower than that of 8-cell embryos and similar to that of half 8-cell stage embryos. In the 4-cell[harr ]8-cell chimaeras the 4-cell stage embryos did not contribute more to the trophectoderm than the ICM derivatives. Thus, differences between 4-cell and 8-cell embryos cannot explain the restricted tissue distribution of tetraploid cells previously reported for 4-cell tetraploid[harr ]8-cell diploid chimaeras. It is suggested that cells from the more advanced embryo are more likely to contribute to the ICM but, for technical reasons, are prevented from doing so in simple aggregates of equal numbers of whole 4-cell and whole 8-cell stage embryos.

Summary

Actin filaments play an important role in cell division. The present study was designed to examine the relationship between actin filament distribution and pig embryo development. When in vivo matured and fertilised pig oocytes were cultured in TCM 199 or NCSU 23, in various proportions, 45–65% of inseminated oocytes developed to the 2- to 4-cell stages but blastocyst development was observed only in NCSU 23 (34%) or NCSU 23 containing 10% TCM 199 (7%). Supplementation of NCSU 23 medium with 20% or more TCM 199 resulted in no blastocyst formation. Examination of actin filaments indicated that microfilaments were distributed in the cortex, at the junction of blastomeres and in the perinuclear area in the embryos cultured in NCSU 23, but perinuclear actin filaments were not observed in embryos cultured in TCM 199. When 2- to 4-cell stage embryos obtained from TCM 199 were transferred to NCSU 23 medium at 36 h after in vivo fertilisation, 57% of the cleaved embryos developed to blastocysts, which was no different from the proportion obtained after culture in NCSU 23 alone (56%). In addition, when 2- to 4-cell stage embryos obtained from TCM 199 were transferred to NCSU 23, most embryos showed perinuclear actin filaments within 6 h. The results indicate that the composition of the culture medium plays an important role in the polymerisation of actin filaments, which in turn influences embryo development. It is possible that pig embryo development was blocked by some components in TCM 199 which prevented actin filament polymerisation.

A common early feature in the activation of all eggs during fertilisation is an increase in the level of intra-cellular free calcium (Ca2+) that, in most species, propagates as a wave across the egg (reviewed in Strieker, 1999). In echinoderms, this Ca2+ release is the result of a signal transduction cascade that requires phospholipase Cγ (PLCγ)-mediated production of inositol trisphosphate (IP3) (Carroll et al., 1997, 1999). PLCγ is most commonly regulated by tyrosine phosphorylation (Rhee & Bae, 1997), indicating that a tyrosine kinase is a likely upstream regulator of PLCγ enzymatic activity at fertilisation. In support of this hypothesis, an increase in tyrosine kinase activity and an increase in tyrosine-phosphorylated proteins at fertilisation has been observed in echinoderm eggs (Satoh & Garbers, 1985; Ciapa & Epel, 1991; Kinsey, 1997). Moreover, the tyrosine kinase inhibitors genistein (Shen et al., 1999) and PP1 (Abassi et al., 2000) have been used to show that in sea urchin eggs a tyrosine kinase activity is required for normal Ca2+ release in response to fertilisation.

In eggs of the starfish Asterina miniata, a Src-type tyrosine kinase has been identified as a potential regulator of PLCγ activity at fertilisation (Giusti et al., 1999a). This kinase exhibits a rapid fertilisation-dependent association specifically with the Src Homology 2 (SH2) domains of PLCγ. Moreover, the timing of this association correlates with an increase in the tyrosine kinase activity bound to the PLCγ SH2 domains, and neither the Src kinase nor the associated kinase activity was observed to associate with the PLCγ SH2 domains after treating eggs with the calcium ionophore A23187 (Giusti et al., 1999a). These data identify an egg Src family kinase as a potential upstream regulator of PLCγ during starfish egg fertilisation.

In the present study the role of glycosphingolipids (GSL) in amphibian development was investigated. We analysed the de novo synthesis of neutral GSL and gangliosides through the initial stages of Bufo arenarum embryo development and their participation during gastrulation using 1-phenyl-2-palmitoyl-3-morpholino-1-propanol (PPMP), a potent inhibitor of glucosylceramide synthase. Ganglioside synthesis began at the blastula stage and reached a maximum during gastrulation (stages 10-12) while neutral GSL synthesis showed a slight gradual increase, the former being quantitatively more significant than the latter. Ganglioside synthesis was reduced by 90% while neutral GSL synthesis was inhibited by 65% when embryos at blastula stage were cultured for 24 h in 20 μM PPMP. The depletion of GSL from amphibian embryos induced an abnormal gastrulation in a dose-dependent manner. We found that PPMP had a pronounced effect on development since no embryos exhibited normal gastrulation; their developmental rate either slowed down or, more often, became totally arrested. Morphological analysis of arrested embryos revealed inhibition of the gastrulation morphogenetic movements. Analysis of mesodermal cell morphology in those embryos showed a severe decrease in the number and complexity of cellular extensions such as filopodia and lamellipodia. Mesodermal cells isolated from PPMP-treated embryos had very low adhesion percentages. Our results suggest that glycosphingolipids participate in Bufo arenarum gastrulation, probably through their involvement in cell adhesion events.

Efforts to achieve complete chemical definition of media used for in vitro capacitation of bovine spermatozoa including removal of heparin purified from porcine intestinal mucosa are presented. Fluorescent staining with chlortetracycline (CTC), known to reflect changes coincident with sperm capacitation in certain species, was studied following treatments of frozen-thawed bull spermatozoa with β-cyclodextrins, dibutyryl cAMP (dbcAMP) and progesterone in comparison with heparin. The CTC staining patterns (F, B and AR) were confirmed to correlate with known conditions that effectively prepare cryopreserved bull spermatozoa for fertilisation in vitro. In the absence of glucose, the routinely employed heparin-containing capacitating medium caused an increase in spermatozoa displaying the AR pattern. Both progesterone (100 μM) and dbcAMP (0.01–0.1 mM) were able to increase the proportion of B pattern stained sperm cells more than after exposure to control (mDM) conditions without a significant reduction in motility. Exposure to either dbcAMP or β-cyclodextrins was accompanied by an increase in proportions of spermatozoa displaying the AR pattern over those seen in controls. Exposure to β-cyclodextrins did not increase the proportion of B pattern stained spermatozoa. Comparison of spermatozoa from two bulls revealed differential responses of spermatozoa from different males to treatments with heparin and progesterone. In vitro fertilisation results demonstrated that previously cryopreserved bull spermatozoa could be capacitated in chemically defined conditions devoid of heparin or other biological components.

In starfish ovaries follicle cells that envelop each oocyte are thought to mediate the production of a maturation inducing substance (MIS), identified as 1-methyladenine, that induces maturation and spawning of oocytes after exposure to a gonadotropic substance secreted by the radial nerve (RNF). Studies were carried out to assess the possible role of extrafollicular cells within the ovarian wall in mediating this signal transduction process in the ovary of Pisaster ochraceus. Oocyte maturation and spawning occurred following the addition of RNF to intact ovarian tissue in vitro whereas no maturation occurred following the addition of RNF to germinal vesicle (GV) oocytes or GV oocytes surrounded by follicle cells. In contrast, oocyte maturation occurred when small ovarian wall fragments, lacking mature follicles, were incubated with GV oocytes and RNF. Neither actinomycin D nor cycloheximide altered RNF induction of oocyte maturation in the presence of the ovarian wall tissue whereas preheating (boiling water for 5 min) the tissue obliterated its response to RNF. Non-ovarian tissues failed to produce MIS in response to RNF. Results suggest that ovarian components other than the follicle cells that envelop fully grown immature oocyte are responsive to RNF and represent a significant and previously unrecognised intra-ovarian source of MIS.

Cell death occurs during early development in vivo and in vitro, although little is known about the mechanism of blastomere death and the relation to embryonic loss. Apoptosis, characterised by chromatin condensation, DNA fragmentation and membrane blebbing, occurs without damage to surrounding cells in contrast to necrosis. Bovine oocytes and in vitro fertilised embryos (total n = 449) were analysed for (1) DNA fragmentation using terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) and (2) morphological features of apoptosis. TUNEL labelling was detected in immature and mature oocytes (7%, n = 57 and 23%, n = 60, respectively), and at least one cell of 8- to 16-cell embryos (5%, n = 57), morulae/early blastocysts (79%, n = 39) and expanded/hatched blastocysts (100%, n = 48). In contrast, TUNEL labelling was not detected in zygotes (n = 61), 2-cell embryos (n = 46) or 3- to 7-cell embryos (n = 81). Chromatin condensation, nuclear fragmentation, absence of neighbouring cell destruction and extrusion of cells was frequent among advanced stage embryos. Although not detected during early cleavage under standard conditions, TUNEL labelling indicative of apoptosis was induced by treatment with 10 μM staurosporine for 30 h in 95% of cleavage stage embryos (n = 59). Determination of the expression and localisation of the p53 tumour suppressor gene using reverse transcription polymerase chain reaction and whole-mount immunofluorescence revealed that although p53 transcripts were present throughout early development, nuclear localisation of p53 protein could not be detected in any blastocyst suggesting p53-independent apoptosis. This study has shown that apoptosis is dependent on embryonic developmental stage after standard culture. This suggests that bovine embryos become more capable of accommodating damaged or abnormal cells as development proceeds.