Early embryonic development is largely dependent on maternal RNAs and proteins synthesised during oogenesis. Zygotic transcription is an essential event that occurs at a species-specific time after fertilisation. In the absence of zygotic transcription the embryo dies since it can no longer support requirements for successful embryo development. Molecular genetics of gene expression during early embryogenesis, especially in the bovine species, remain one of the unsolved questions in modern biology. Earlier studies suggested that embryonic transcription in cattle begins at the late 4-cell or 8-cell stage. However, more recent studies suggest that bovine zygotes and 2-cell embryos are both transcriptionally and translationally active. Moreover, changes in chromatin structure due to acetylation of core histones and DNA replication play important roles in the regulation of zygotic/embryonic gene expression. This review will summarise results of recent studies about the timing and mechanisms of zygotic/embryonic gene expression in cattle. In addition, terminology in the literature regarding gene expression during early embryogenesis will be clarified. These terminologies include: ‘zygotic/embryonic gene expression’, ‘maternal to embryonic transition in control of development (MET)’ and ‘zygotic/embryonic genome activation (ZEGA)’.

Spermatozoa leaving the testis of normal animals are not ready to fertilise oocytes. They gain this ability while passing through the epididymis. It is interesting that spermatozoa of most animals take about 10 days to pass through the epididymis despite huge interspecies variations in the length of the epididymal tubule (e.g. some 30–50 m in large farm animals and about 1 m in the laboratory mouse) (Robaire & Hermo, 1988). The site where the spermatozoa begin to acquire fertilising capacity varies according to species, but it is generally the corpus epididymis or the proximal segment of the cauda epididymis where a large proportion of the spermatozoa become fertilisationcompetent. The distal segment of the cauda epididymis is the principal site for the storage of mature spermatozoa. Prolonged sojourn in the cauda epididymis (and vas deferens), however, could be detrimental to the spermatozoa.

The genome of all cells is protected at all times by mechanisms collectively known as DNA repair activity (DRA). Such activity is particularly important at the beginning of human life, i.e. at fertilization, immediately after and at the very onset of embryonic development. DRA in early development is, by definition, of maternal origin: the transcripts stored during maturation, need to control the integrity of chromatin, at least until the maternal/zygotic transition at the 4- to 8-cell stage in the human embryo. Tolerance towards DNA damage must be low during this critical stage of development. The majority of DNA damage is due to either apoptosis or reactive oxygen species (ROS). Apoptosis, abortive or not, is a common feature in human sperm, especially in oligoasthenospermic patients and FAS ligand has been reported on the surface of human spermatozoa. The susceptibility of human sperm to DNA damage is well documented, particularly the negative effect of ROS (Kodama et al., 1997; Lopes et al., 1998a, b) and DNA modifying agents (Zenzes et al., 1999; Badouard et al., 2007). DNA damage in sperm is one of the major causes of male infertility and is of much concern in relation to the paternal transmission of mutations and cancer (Zenzes, 2000; Aitken et al., 2003; Fernández-Gonzalez, 2008). It is now clear that DNA damaged spermatozoa are able to reach the fertilization site in vivo (Zenzes et al., 1999), fertilize oocytes and generate early embryos both in vivo and in vitro. The effect of ROS on human oocytes is not as easy to study or quantify. It is a common consensus that the maternal genome is relatively well protected while in the maturing follicle; however damage may occur during the long quiescent period before meiotic re-activation (Zenzes et al., 1998). In fact, during the final stages of follicular growth, the oocyte may be susceptible to damage by ROS. With regards to the embryo there is active protection against ROS in the surrounding environment i.e. in follicular and tubal fluid (El Mouatassim et al., 2000; Guerin et al., 2001). DNA repair activity in the zygote is mandatory in order to avoid mutation in the germ line (Derijck et al., 2008). In this review we focus on the expression of mRNAs that regulate DNA repair capacity in the human oocyte and the mechanisms that protect the embryo against de novo damage.

Sand dollar eggs were microinjected with botulinum C3 exoenzyme, an ADP-ribosyltransferase from Clostridium botulinum that specifically ADP-ribosylates and inactivates rho proteins. C3 exoenzyme microinjected during nuclear division interfered with subsequent cleavage furrow formation. No actin filaments were detected in the equatorial cortical layer of these eggs by rhodamine-phalloidin staining. When microinjected into furrowing eggs, C3 exoenzyme rapidly disrupted the contractile ring actin filaments and caused regression of the clevage furrows. C3 exoenzyme had no apparent effect on nuclear division, however, and multinucleated embryos developed from the microinjected eggs. By contrast, C3 exoenzyme did not affect the organisation of cortical actin filaments immediately after fertilisation. Only one protein (molecular weight 22000) was ADP-ribosylated by C3 exoenzyme in the isolated cleavage furrow. This protein co-migrated with ADP-ribosylated rhoA derived from human paltelets when analysed by two-dimensional gel electrophoresis. These results strongly suggest that a rho-like, small GTP-binding protein is selectively in the organisation and maintenance of the contractile ring.

The effect of temperature fluctuation on spindle integrity and chromosomal organisation in the human oocyte, and the consequences of such effects on the chromosomal constitution of resulting parthenotes, were investigated. A total of 340 oocytes were stained immunocytochemically with an antibody to α-tubulin, and 502 were activated parthenogenetically. Exposure of oocytes to room temperature for 2, 10 or 30 min caused disruption of the spindle in 77%(n = 26),72%(n = 18) and 89% (n = 19) of cases respectively, with evidence of chromosomal dispersal in 50%,56% and 52.6% respectively. These effects were reversed when oocytes were returned to 37°C after exposure to room temperature for 2 min, but not after 10 min or 30 min: Temperature reduction affected rates of parthenogenetic activation of oocytes (2 min: 67%, n = 27; 10 min: 68%, n = 28; 30 min; 54%, n = 35) and cleavege of resulting parthenotes, but only if oocytes were exposed to room temperature for 30 min (30 min: 53%, n = 19).There is a direct association between temperature-induced spindle damage in the oocyte(70%, 50 of 63) and chromosomal abnormalities in parthenotes developed from oocytes exposed to room temperature (56%,23 of 41; P < 0.01).

Oocytes, in general, are greatly enriched in mitochondria to support higher rates of macromolecular synthesis and critical physiological processes characteristic of early development. An inability of these organelles to amplify and/or to accumulate ATP has been linked to developmental abnormality or arrest. The number of mitochondrial genomes present in mature mouse and human metaphase II oocytes was estimated by fluorescent rapid cycle DNA amplification, which is a highly sensitive technique ideally suited to quantitative mitochondrial DNA (mtDNA) analysis in individual cells. A considerable degree of variability was observed between individual samples. An overall average of 1.59 × 105 and 3.14 × 105 mtDNA molecules were detected per mouse and human oocyte, respectively. Furthermore, the mtDNA copy number was examined in polar bodies and contrasted with the concentration in their corresponding oocytes. In addition, the density of mtDNA in a cytoplasmic sample was estimated in an attempt to determine the approximate number of mitochondria transferred during clinical cytoplasmic donation procedures as well as to develop a clinical tool for the assessment and selection of oocytes during in vitro fertilisation procedures. However, no correlation was identified between the mtDNA concentration in either polar bodies or cytoplasmic samples and their corresponding oocyte.

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.

Ocean acidification is now recognized as a threat to marine ecosystems; however, the effect of ocean acidification on fertilization in marine organisms is still largely unknown. In this study, we focused on sperm flagellar motility in broadcast spawning reef invertebrates (a coral and a sea cucumber). Below pH 7.7, the pH predicted to occur within the next 100 years, sperm flagellar motility was seriously impaired in these organisms. Considering that sperm flagellar motility is indispensable for transporting the paternal haploid genome for fertilization, fertilization taking place in seawater may decline in the not too distant future. Urgent surveys are necessary for a better understanding of the physiological consequences of ocean acidification on sperm flagellar motility in a wide range of marine invertebrates.

Mouse antral oocytes can be classified in two different types termed SN or NSN oocytes, depending on the presence or absence, respectively, of a ring of Hoechst 33342-positive chromatin surrounding the nucleolus. The aim of the present study was to test the developmental competence to blastocyst of the two types of oocytes. Here we show that following isolation, classification and culture of cumulus-free antral oocytes, 14.7% and 74.5% of NSN and SN oocytes, respectively, reached the metaphase II stage. When fertilised and further cultured none of the metaphase II NSN oocytes developed beyond the 2-cell stage whilst 47.4% of the metaphase II SN oocytes reached the 4-cell stage and 18.4% developed to blastocyst. The findings reported in this paper may contribute to improved procedures of female gamete selection for in vitro fertilisation of humans and farm animals. Furthermore, the selection of oocytes with better developmental potential may be of interest for studies on nuclear/cytoplasm interaction, particularly in nuclear-transfer experiments.

A new methodology for blastocyst biopsy that uses a 1.48μm in diode laser is described. Trophectoderm cells are biopsied after laster zona drilling and culture, fixed and processed for fluorescent in situ hybridisation (FISH) analysis. Preliminary results on the efficiency of the procedure and blastocyst recovery rate are promising. Blastocyst laser biopsy is a useful tool in preimplantation genetic diagnosis (PGD) as it allows a more reliable diagnosis and widens the diagnostic possibilities on account of the higher number of cells obtained in the biopsy.

Careful attention has been focused recently on DNA quality in human IVF. Therefore a variety of methods has been developed to evaluate DNA integrity, especially concerning fragmentation. Using liquid chromatography and mass spectrometry (LC/MS/MS) for our best sperm samples, we have established reference values for several oxidative lesions, in order to gain insights into the cause of DNA lesions. Besides 8-oxodeoxyguanosine, we found rather high levels of two ethenonucleosides: 1,N6-ethenoadenosine and 1,N2-ethenoguanosine. These compounds probably arise from a reaction with 4-hydroxy-2-nonenal, the main aldehyde compound released during lipid peroxidation, or after occupational exposure to vinyl chloride. The quantity of chlorinated bases detected is low. All of this decay has to be repaired by the oocytes at the time of fertilization or immediately after. This aspect should not be overlooked in assisted reproductive technology, in order to understand risks and limitations.

Fertilisation and development of dysmorphic human oocytes recovered from hyperstimulated ovaries have been evaluated following intracytoplasmic sperm injection (ICSI) for treatment of male infertility. A total of 2968 oocytes at metaphase II of meiosis were injected, of which 806 (27.2%) were dysmorphic at the light microscopic level. Cytoplasmic abnormalities included granularity, areas of necrosis, organelle clustering, vacuoles, and accumulating saccules of smooth endoplasmic reticulum. Anomalies of the first polar body and zona pellucida, as well as non-spherical shapes of oocytes, were also noted. Contrary to previous findings linking some dysmorphisms to non-assisted fertilisation failure, in this study no single abnormality led to a reduction in the fertilisation rate, nor was fertilisation compromised in oocytes with multiple abnormalities. The incidence of normal fertilisation (two pronuclei and two polar bodies) was 69% in both the dysmorphic and non-dysmorphic oocytes. While overall pregnancy and implantation results were not altered in the group of patients (n = 242) in whom at least one dysmorphic oocyte was injected, exclusive replacement of embryos which originated from dysmorphic oocytes led to a higher incidence of early pregnancy loss. It is concluded that aberrations in the morphology of human oocytes – most probably a product of controlled ovarian stimulation – are of little or no consequence to fertilisation or early cleavage after ICSI. It is possible, however, that these embryos have a reduced potential for implantation and further development.

MicroRNAs (miRNAs) are small endogenous molecules that are involved in a diverse of cellular process. However, little is known about their abundance in bovine oocytes and their surrounding cumulus cells during oocyte development. To elucidate this situation, we investigated the relative expression pattern of sets of miRNAs between bovine oocyte and the surrounding cumulus cells during in vitro maturation using miRNA polymerase chain reaction (PCR) array. Results revealed that a total of 47 and 51 miRNAs were highly abundant in immature and matured oocytes, respectively, compared with their surrounding cumulus cells. Furthermore, expression analysis of six miRNAs enriched in oocyte miR-205, miR-150, miR-122, miR-96, miR-146a and miR-146b-5p at different maturation times showed a dramatic decrease in abundance from 0 h to 22 h of maturation. The expression of the same miRNAs in preimplantation stage embryos was found to be highly abundant in early stages of embryo development and decreased after the 8-cell stage to the blastocyst stage following a typical maternal transcript profile. Similar results were obtained by localization of miR-205 in preimplantation stage embryos, in which signals were higher up to the 4-cell stage and reduced thereafter. miR-205 and miR-210 were localized in situ in ovarian follicles and revealed a spatio-temporal expression during follicular development. Interestingly, the presence or absence of oocytes or cumulus cells during maturation was found to affect the expression of miRNAs in each of the two cell types. Hence, our results showed the presence of distinct sets of miRNAs in oocytes or cumulus cells and the presence of their dynamic degradation during bovine oocyte maturation.

The present study examines the use of buffalo preantral follicles as a source of oocytes for in vitro embryo production. Preantral follicles were isolated from abattoir-derived buffalo ovaries and were grown for 100 days in five different culture systems: (1) minimum essential medium (MEM); (2) coconut water; (3) MEM + ovarian mesenchymal cell (OMC) co-culture; (4) MEM + granulosa cell (GC) co-culture; or (5) MEM + cumulus cell (CC) co-culture. Low growth rates for the preantral follicles were observed when follicles were cultured in MEM or coconut water medium. Moderate growth rates were seen for OMC and GC co-cultures, and high rates of growth were observed when follicles were grown in CC co-culture. The survival of preantral follicles was low in the MEM culture (<25%), but was over 75% in the other culture systems. Oocytes were not recovered from the MEM group, while an oocyte recovery rate of 80–100% was observed when the follicles were cultured with coconut water/somatic cells. Transferable embryos could be produced only with the oocytes obtained from preantral follicles grown in the OMC and CC co-culture systems. This study demonstrates, for the first time, that it is possible to produce buffalo embryos by in vitro fertilization of oocytes derived from in vitro grown preantral follicles.

A 2×3 factorial designed experiment was conducted in order to examine whether freeze-dried rat spermatozoa can participate in full-term development following intracytoplasmic sperm injection (ICSI). A sperm suspension from cauda epididymides of Sprague–Dawley (SD) rats was prepared with or without ultrasonic treatment. The sonicated and non-sonicated sperm suspensions were processed for freeze-thawing (FT groups; 100μl sample was cooled in liquid nitrogen vapor, stored for 1 day at −196 °C, and thawed in a 25 °C water bath) and freeze-drying (FD groups; 100 μl sample was frozen in liquid nitrogen for 20 s, lyophilized for 6 h, stored at 4 °C for 2 days, and rehydrated with 100μl ultrapure water), or were subjected to immediate use for ICSI (fresh control groups). The sperm heads were microinjected into denuded SD oocytes using a piezo-driven micropipette 2–4μm in diameter. The presumptive zygotes were transferred into oviducts of pseudopregnant Wistar female rats. Viable rat offspring were produced from all six experimental groups. Ultrasonic treatment of rat spermatozoa was effective in increasing the offspring rate (23.3% vs 6.7% in fresh control groups, 35.0% vs 7.6% in FT groups, 9.2% vs 2.5% in FD groups). The acrosomal region appeared to be intact even after ultrasonic FT and FD treatments as well as in the fresh controls, while the lateral dorsal region of the sperm membrane was more or less damaged in the sonicated, FT and FD samples. Thus, the successful participation of freeze-dried spermatozoa in full-term development was demonstrated by applying ICSI in the rat.

Polyamines are polycationic molecules that contain two or more amino groups (–NH3+) and are present in all eukaryotic and prokaryotic cells. Polyamines are synthesized from arginine, ornithine, and proline, and from methionine as the methyl-group donor. In the traditional pathway for polyamine synthesis, arginase converts arginine into ornithine, which is decarboxylated by ornithine decarboxylase (ODC1) to generate putrescine. The latter is converted to spermidine and spermine. Recent studies have indicated the existence of ‘non-classical pathways’ for the generation of putrescine from arginine and proline in animal cells. Specifically, arginine decarboxylase (ADC) catalyzes the conversion of arginine into agmatine, which is hydrolyzed by agmatinase (AGMAT) to form putrescine. Additionally, proline is oxidized by proline oxidase to yield pyrroline-5-carboxylate, which undergoes transamination with glutamate to produce ornithine for decarboxylation by ODC1. Intracellular production of polyamines is controlled by antizymes binding to and inactivating ODC1. Polyamines exert effects that include stimulation of cell division and proliferation, gene expression for the survival of cells, DNA and protein synthesis, regulation of apoptosis, oxidative stress, angiogenesis, and cell–cell communication activity. Accordingly, polyamines are essential for early embryonic development and successful pregnancy outcome in mammals. In this paper the main concepts on the history, structure and molecular pathways of polyamines as well as their physiological role on angiogenesis, and reproductive physiology are reviewed.

Evaluation of apoptosis and expression level of apoptosis-related genes is useful for examining the variation in embryo quality according to environmental change. The objective of this study was to investigate DNA fragmentation and apoptosis-related gene expression patterns in frozen-thawed bovine blastocysts. In vitro produced day 7 blastocysts were frozen by two different vitrification methods (conventional 0.25 ml straw or MVC straw). After thawing, DNA fragmentation of surviving embryos was examined by TUNEL assay, and the expression patterns of their apoptotic genes (survivin, Fas, Hsp 70 and caspase-3) were evaluated using real-time quantitative reverse transcriptase polymerase chain reaction. In vitro survival rates of frozen-thawed embryos were higher following the MVC vitrification method (88.2% re-expanded at 24 h, 77.1% hatching at 48 h) than the conventional (C) vitrification method (77.0% re-expanded at 24 h, 66.7% hatching at 48 h). However, both vitrified methods resulted in a significantly higher apoptotic index (C vitrification method 11.9%, MVC vitrification method 11.0%) than in non-frozen embryos (3.0%). Expression levels of survivin, Fas, caspase-3, and Hsp 70 were also increased in the frozen-thawed embryos compared with non-frozen embryos. These results indicate that the cryopreservation procedure might cause damage that results in an increase in DNA fragmentation and apoptosis-related gene transcription, reducing developmental capacity of frozen-thawed embryos.

The involvement of cumulus cells and chromatin organisation in transcriptional activity was investigated. In addition, the relationship between transcriptional activity and meiotic competence in fully grown mouse oocytes was surveyed. Transcriptional activity was detected in fully grown oocytes in which chromatin did not surround the nucleolus in the germinal vesicle (NSN-type oocytes), but not in oocytes in which chromatin surrounded the nucleolus (SN-type oocytes). Cumulus cells seemed to downregulate transcriptional activity in NSN-type oocytes, since transcriptional activity was 3 times greater in the denuded NSN-type oocytes free of cumulus cells (DO oocytes) than in NSN-type oocytes enclosed in cumulus cells (COC oocytes). Higher transcriptional activity corresponded to lower germinal vesicle breakdown (GVB) competence of fully grown oocytes in culture. Although GVB occurred in nearly all (99%) the SN-type oocytes, it occurred in 88% of COC/NSN-type oocytes (cumulus-oocyte complex with SN-type configuration) and in 61% of DO/NSN-type oocytes (denuded oocytes with NSN-type configuration). There was a negative correlation between transcriptional activity and the capacity of a cell to complete the progression to the second metaphase (MII). In GVB oocytes, the percentage of first polar body (PBI) extrusion differed among COC/NSN-type (81%), DO/SN-type (66%), COC/NSN-type (47%) and DO/NSN-type (29%) oocytes. After activation with 10 mM Sr2+, the frequency of parthenogenetic activation was greater in SN-type oocytes (46.9%) than in transcriptionally active NSN-type oocytes (27.5%). These results suggest that transcriptional activity has a detrimental effect on the competence of meiotic maturation and subsequent activation in fully grown GV oocytes. Alternatively, active transcription in the fully grown oocytes suggests that they are still in the process of synthesising substances required for meiotic maturation and are not yet competent for these processes.

Adducin is a cytoskeletal protein that can function in vitro to bundle F-actin and to control the assembly of the F-actin/spectrin cytoskeletal network. The Drosophila Adducin-like (Add) locus (also referred to as hu-li tai shao (hts)) encodes a family of proteins of which several are homologous to mammalian adducin (Ding et al., Proc. Natl. Acad. Sci. USA90, 2512–16, 1993; Yue & Spradling, Genes Dev.6, 2443–54, 1992). We report the identification of two novel adducin isoforms: a 95 × 103Mr form (ADD-95) and an 87 × 103Mr form (ADD-87). We present a detailed analysis of the distribution patterns of ADD-95 and ADD-87 during oogenesis and embryogenesis. The isoforms are co-expressed in several cell- and tissuetypes; however, only ADD-87 is present in mid- to late-stage oocytes. ADD-87 is present throughout the oocyte cortex at stages 9 and 10 of oogenesis but is detectable only at the anterior pole from stage 11 onward, correlated with localisation of Add-hts mRNA first to the cortex and then to the anterior pole of the oocyte. ADD-87 co-localises with F-actin and spectrin in the cortex of the oocyte through stage 10 of oogenesis, consistent with a possible role in cytoskeletal assembly or function predicted by mammalian studies.

Global activation of the embryonic genome occurs at the 4– to 8–cell stage in human embryos and is marked by continuation of early cleavage divisions in the presence of transcriptional inhibitors. Here we demonstrate, using recerse transcripase–polymerase chin reaction (Rt–PCR), the presence of transcripts for wo paternal Y chromosomal genes, ZFY and SRY in human preimplantation embryos. ZFY transcripts were detected as early as the pronucleate stage, 20–24 h post-insemination In vitro and at intermediate stages up to the blastocyst stage. SRY Transcripts were also detected at 2–cell to blastocyos observed in many mammalian species focuses attention on the role of events in six determination prior to gonad differentiation.