Zygote 

About: Zygote is an academic journal published by Cambridge University Press. The journal publishes majorly in the area(s): Oocyte & Sperm. It has an ISSN identifier of 0967-1994. Over the lifetime, 1747 publications have been published receiving 26822 citations.

Zygotic and embryonic gene expression in cow: a review of timing and mechanisms of early gene expression as compared with other species.

Abstract: 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 fertilization. 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)'.

Fertility of mammalian spermatozoa: its development and relativity.

Abstract: 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.

A rho-like protein is involved in the organisation of the contractile ring in dividing sand dollar eggs.

Abstract: 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 cleavage 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 22,000) was ADP-ribosylated by C3 exoenzyme in the isolated cleavage furrow. This protein co-migrated with ADP-ribosylated rhoA derived from human platelets when analysed by two-dimensional gel electrophoresis. These results strongly suggest that a rho-like, small GTP-binding protein is selectively involved in the organisation and maintenance of the contractile ring.

DNA damage and repair in human oocytes and embryos: a review

Abstract: 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; Fernandez-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.

Apoptosis in the early bovine embryo

Abstract: 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 microM 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.