Regulation of early embryo development: functional redundancy between cyclin subtypes

Vinclozolin-induced mouse penile malformation and "small testis" via miR132, miR195a together with the Hippo signaling pathway

Vinclozolin (VCZ) is a fungicide with antiandrogen activity. Exposure to VCZ in maternal uterus may cause uterine, ovarian and testicular damage, hypospadias and prostate abnormality in the offspring. Hippo pathway, which is highly conservative and may be activated by miR132 and miR195a, can control organ size and tissue regeneration, and participate in injury and deformity. In the present study, VCZ was found to have caused penile malformation in the male offspring and also induced "small testis" when it was administered to the pregnant mice orally at a dose of 400 mg kg^-1 day^-1 on Days 12-18 of gestation. At 1, 3 and 7 weeks of age, VCZ could increase miR132, Mst1, Sav1, phosphorylated Yes-associated protein (pYap) and pLats, and decrease Yap in offspring penises and testes. Besides, it could also raise miR195a both in the testes of 1, 7-week and in the penises of all the three ages. In addition, we found the levels of some cyclin (Ccn) genes elevated in the testes, the expression of the androgen receptor (Ar) gene dereased and Jnks changed in the penises of offspring aged 1, 3 and 7 weeks. The results suggest that that gestational VCZ exposure could not only increase miR132 and miR195a in penises and testes of the offspring, but also activate Hippo pathway and down-regulate Ar. These may directly inhibit cell proliferation, accelerate cell death by up-regulating the expression of some Ccns, and ultimately lead to penile and testicular damage and malformations in the offspring.

Melatonin slightly alleviates the effect of heat shock on bovine oocytes and resulting blastocysts

Heat stress is associated with increased production of reactive oxygen species (ROS) and disruption of bovine oocyte function. Here, we examined whether the antioxidant melatonin can alleviate the deleterious effects of heat stress on oocyte developmental competence. Cumulus-oocyte complexes were matured for 22 h at 38.5 °C (control) or for 22 h at 41.5 °C (heat shock) with or without 1.0 × 10^-7 M melatonin. At the end of maturation, a subgroup of oocytes was examined for nuclear and cytoplasmic maturation, ROS level and mitochondrial membrane potential. A second subgroup of oocytes underwent fertilization (18 h), and putative zygotes were cultured in an incubator equipped with a time-lapse system for ∼190 h. Cleavage rate and the proportion of blastocysts, as well as embryo kinetics were recorded. Expanded blastocysts were collected and their transcript abundance was evaluated. Heat shock increased ROS and reduced the proportion of oocytes that resumed meiosis and reached the metaphase-II stage. Exposing oocytes to heat shock with melatonin alleviated these effects to some extent, expressed by a marginal reduction in ROS level and increased proportion of metaphase-II stage oocytes. Neither the distribution of oocyte cortical granules nor polarization of the mitochondrial membrane differed between control and heat-shocked oocytes cultured with or without melatonin. Heat shock reduced the proportion of embryos that cleaved and developed to blastocysts, characterized by alterations in kinetics of the developed embryos expressed by a delay in the first cleavage, second cleavage and blastocyst formation for heat-shock vs. control groups. Melatonin did not restore the competence or kinetics of embryos developed from heat-shocked oocytes. However, expanded blastocysts developed from heat-shocked oocytes treated with melatonin expressed a higher transcript abundance of genes associated with mitochondrial function, relative to the control and heat-shock group. In summary, melatonin improved the oxidative status of heat-shocked oocytes to some extent and had a beneficial effect on maternal mitochondrial transcripts in the developed blastocysts.

Effect of di-(2-ethylhexyl) phthalate and mono-(2-ethylhexyl) phthalate on in vitro developmental competence of bovine oocytes

In the last decade, potential exposure of humans and animals to industrial chemicals and pesticides has been a growing concern. In the present study, di-(2-ethylhexyl) phthalate (DEHP) and mono-(2-ethylhexyl) phthalate (MEHP) were used to model the effects of endocrine-disrupting compounds and their risk in relation to early embryonic losses. Exposure of cumulus oocyte complexes during maturation to 50 μM MEHP reduced the proportion of oocytes that underwent nuclear maturation (p < 0.05) and increased the proportion of apoptotic oocytes (p < 0.05). Furthermore, phthalates reduced cleavage rate in the MEHP-treated group (p < 0.05) and the proportion of embryos developing to the blastocyst stage in both DEHP- and MEHP-treated groups (p < 0.05). The total cell count for blastocysts developing from MEHP-treated oocytes was lower than in controls (p < 0.05). Exposure of oocytes to MEHP during maturation reduced (p < 0.05) the expression of ASAH1 (an anti-apoptotic factor), CCNA2 (involved in cell cycle control), and POU5F1 (responsible for pluripotency) in matured oocytes. Furthermore, the reduced mRNA expression of POU5F1 and ASAH1 lasted into two-cell stage embryos (p < 0.05). Phthalate-induced alterations in POU5F1, ASAH1, and CCNA2 expression might explain in part the reduced developmental competence of MEHP-treated oocytes.

Expression of Six1 homeobox gene during development of the mouse submandibular salivary gland

BACKGROUND

Members of the Six family of homeoproteins are expressed in numerous tissues during vertebrate embryogenesis, and are critical regulators of both cell proliferation and survival. Here we report the temporal and spatial expression of Six1 during maturation of the mouse submandibular salivary gland (SSG) from embryonic day 18.5 (E18.5) to postnatal day 28. Additionally, we examine the role of Six1 during SSG development using Six1-deficient mice.

METHODS

Six1 expression was assessed by reverse transcription-polymerase chain reaction, Western blot, and immunofluorescence. Proliferation was measured by bromodeoxyuridine (BrdU) incorporation index, and apoptosis was evaluated by TUNEL assay.

RESULTS

Six1 mRNA and protein levels are high in the epithelial SSG cells at E18.5 and decrease progressively in the postnatal maturing SSG. Although SSGs from Six1(-/-) embryos are significantly smaller than wild type SSGs, the histological structures of the SSG acini and ducts are similar. Six1(-/-) salivary epithelial cells exhibit an intrinsic defect in cell proliferation accompanied by a significant reduction in the Six1 target gene cyclin A1, previously shown to be a critical mediator of Six1-induced proliferation.

CONCLUSION

Our results suggest that the reduction in size of Six1(-/-) SSGs is result of a decrease in cell proliferation during development/maturation.

Retinoid-dependent mRNA expression and poly-(A) contents in bovine oocytes meiotically arrested and/or matured in vitro

The presence of retinoic acid (RA) during in vitro maturation (IVM) improves bovine oocyte quality and developmental potential. In this work, we investigated the underlying molecular mechanisms. Cumulus-oocyte complexes were meiotically arrested by roscovitine and/or matured in defined medium containing RA, 1% ethanol (vehicle), or no additives. Cumulus-free oocytes were analyzed for poly-(A) mRNA contents and relative mRNA expression of genes involved in cell cycle regulation (cyclin B1 and H1) and antioxidative defence (Mn-superoxide dismutase and glucose-6-phosphate dehydrogenase). Poly-(A) mRNA increased after meiotic inhibition and decreased with IVM completion, both in meiotically arrested and permissively matured oocytes, i.e., matured without previous meiotic arrest. RA dramatically increased poly-(A) mRNA in meiotically arrested oocytes, but more than half of the poly-(A) mRNA disappeared during maturation. Irrespective of oocyte origin, transcripts were detected for all the genes analyzed. IVM, with or without previous meiotic inhibition, increased expression of cyclin B1 and glucose-6-phosphate dehydrogenase, and decreased cyclin H1 and Mn-superoxide dismutase. Except for a decreasing of Mn-superoxide dismutase in meiotically arrested and matured oocytes, RA did not affect mRNA expression. Ethanol led to an abnormal poly-(A) mRNA profile and expression of all the genes analyzed. RA does not modify expression of cyclin B1 and HI genes in the bovine oocyte, and probably does not generate oxidative stress. In addition, RA enhanced mRNA amount as measured by poly-(A) mRNA contents.

Cyclin F disruption compromises placental development and affects normal cell cycle execution

Human cyclin F was originally isolated as a cDNA capable of suppressing the temperature sensitivity of a Saccharomyces cerevisiae cdc4-1 mutant. Its tightly regulated expression and high conservation in the evolutionary progression from amphibians to mammals suggest that it coordinates the timing of a critical cell cycle event. The fact that it contains an F box and can form an SCF (Skp1-Cul1/Cdc53-F-box) complex in vivo further suggests that it may also function in proteolysis. To investigate the role of cyclin F in vivo, we generated mice deficient for cyclin F and conditionally deficient mice as well as mouse embryonic fibroblasts (MEFs) conditionally deficient for cyclin F. Heterozygous animals are normal and fertile, but CycF(-/-) animals, with a myriad of developmental anomalies due in large part to failures in yolk sac and chorioallantoic placentation, die around embryonic day 10.5. Tissue-specific deletion of cyclin F revealed that it was not required for the development and function of a number of different embryonic and adult tissues. In contrast, MEFs lacking cyclin F, while viable, do exhibit cell cycle defects, including reduced population-doubling time and a delay in cell cycle reentry from quiescence, indicating that cyclin F plays a role in cell cycle regulation.

A review of in vitro gamete maturation and embryo culture and potential impact on future animal biotechnology

This review considers the relationship of in vitro gamete maturation and embryo culture to the future development of animal biotechnology. The areas reviewed are oocyte maturation in vitro and embryo culture and their importance for successful in vitro embryo production. The rapidly developing area of spermatogonial cell transplantation and culture is also reviewed. The scientific milestones leading to the development of each area, the problems and prospects for future development and the possible significance of major advances in each area are discussed.

Relative messenger RNA abundance in bovine oocytes collected in vitro or in vivo before and 20 hr after the preovulatory luteinizing hormone surge

In the cyclic cow, final maturation of the ovulatory follicle is initiated by the preovulatory luteinizing hormone (LH) surge. During the subsequent 24 hr period, the oocyte nucleus undergoes meiotic progression to metaphase II and several changes in cytoplasmic organization take place. We have previously shown that oocytes recovered at the time of the LH peak and matured in vitro are less competent to reach the blastocyst stage than their counterparts recovered 20 hr later following in vivo maturation, despite both groups undergoing IVF and culture in parallel. The objective of this study was to compare, using real-time quantitative RT-PCR, the relative abundance of various developmentally important gene transcripts in these oocytes. The groups used were mature bovine oocytes originating from: (1) 2-6 mm follicles from slaughterhouse ovaries; (2) preovulatory follicles punctured by ovum pick-up just before the LH surge (i.e., immature) and matured in vitro; or (3) preovulatory follicles punctured 20 hr later, just prior to ovulation (i.e., in vivo matured). In addition, immature oocytes from 2-6 mm follicles were examined. We examined the relative mRNA expression of five enzymes involved in protection against free oxygen radicals (mitochondrial Mn-superoxide dismutase, MnSOD, cytosolic Cu/Zn superoxide dismutase, Cu/ZnSOD, gamma-glutamyl-cysteine transferase, GCS, glutathione peroxidase, GPX, sarcosine oxidase, SOX), a transcript involved in follicular development (growth differentiation factor-9, GDF-9), transcripts involved in glucose metabolism (glucose-6-phosphate dehydrogenase, G6PDH, glucose transporter type-1 and -8, Glut-1, Glut-8) and genes involved in cell cycle events, Cyclin A and B, and poly(A) polymerase (PAP). Transcripts for all genes were detected, irrespective of oocyte origin. While differences were not significant in all cases, variations in levels of transcript abundance between the groups were related to developmental competence. In particular, transcripts for GDF-9 were expressed at significantly higher levels in oocytes recovered at the LH peak and matured in vitro than in those matured in vivo. The observations with GDF-9 are interesting as this gene is believed to be essential for normal folliculogenesis and may be important in the regulation of early follicle and oocyte growth. In conclusion, the results of this study demonstrate differences in the relative mRNA abundance of several developmentally important gene transcripts in bovine oocytes which may be related to developmental competence.

Time and development

The role that biological timers play in gametogenesis and development is reviewed through use of selected examples. Some general features of biological timers are also reviewed, and two types of timing mechanism are discussed in more detail: circadian rhythms and cell-cycle-based timers. In particular, the recent evidence that oscillatory ion channel activity may play an important role in timing mechanisms is summarized. The activity and properties of an oscillatory K(+) channel present during preimplantation mouse development are described, and preliminary results from its neutralization are discussed.

Aspects of the molecular regulation of early mammalian development

Many regulatory systems operate in the early mammalian embryo. This brief overview surveys several systems and their integration including polarities and axes, left-right differentiation, timers in cells, tissues and in gene expression, and imprinting. Polarities are essential from the very earliest stages of oocyte formation, and maintain their significance until blastocyst stages and beyond. They determine cleavage axes and the distribution of maternal proteins in the oocyte, distinct distributions being identified at the animal pole especially. Left-right axes are no doubt expressed from the earliest embryonic stages, and perhaps even in determining slight differences in the axes of cleavage and of maternal protein distribution. Timers, equally fundamental, have been demonstrated to control many functions in oocytes and embryos. Many fundamental processes in early mammalian oocytes and embryos are closely timed. They are classified into circadian rhythms, hourglass timers, clocks regulating major aspects of development including transcription, longevity via telomere clocks and long-range systems. Imprinting and methylation, increasingly important in establishing stable phenotypes in early embryos, might develop abnormally under some circumstances including intracytoplasmic sperm injection and cloning. A general summary briefly describes some other aspects of regulation, especially chromosomal anomalies in human embryos.