[Malformations in rabbit embryos after maternal blood loss].
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A comparative study of the mechanisms by which X-irradiation and genetic mutation cause loss of vibrissae in embryo mice.
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Animals↗
[Comparative study of reproduction in 4 genetic varieties of Biomphalaria glabrata (Say 1818). II - Embryonal development, hatching and loss of eggs and embryos].
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Animals↗
Imprinting defects in mouse embryos: stochastic errors or polymorphic phenotype?
Defects in expression of imprinted genes are believed to cause developmental abnormalities and play a role in carcinogenesis. To determine whether spontaneous imprinting defects may occur in mouse embryos, we studied the expression of two imprinted genes H19 and Igf2 in individual postimplantation 7.5 d.p.c. and 8.5 d.p.c. embryos. Biallelic expression of H19 was found in 1.6% of the embryos, whereas biallelic expression of Igf2 was found in 0.5% of the embryos. The loss of H19 imprinting (LOI) observed in a small fraction of early postimplantation embryos may be purely stochastic. Alternatively, since we never observed it in an inbred background, it may depend on genetic factors acting in trans. Either mechanism could explain the occurrence of polymorphic imprinting as well as the genesis of sporadic imprinting defects, including cancer. The frequency of LOI of H19 was higher than the incidence of sporadic imprinting disorders in humans (about 1 in 20,000). This contradiction may be explained by different incidence of imprinting errors in different imprinted regions of the genome, in different species, or by loss of the majority of nonmosaic embryos with imprinting defects before birth.
Alleles↗
Induction of tolerance to fast desiccation in black spruce (Picea mariana) somatic embryos: relationship between partial water loss, sugars, and dehydrins.
Events associated with the induction of tolerance to fast desiccation in black spruce (Picea mariana) somatic embryos were investigated. An experimental approach using an initial period of partial water loss was developed to induce either no, partial, or complete tolerance to fast desiccation. Tolerance to subsequent fast desiccation was not promoted by decreasing embryo water content from 1.5 to 1.1 g H2O g-1 DW (g g-1) throughout the first 24 h of slow desiccation. However, tolerance increased from 10 to 95% germination during the second 24-h period of slow desiccation after partial water loss from 1 to 0.55 g g-1. Emphasis was also placed on the relationship between observed tolerance, and sugar and dehydrin contents. Compared to controls, sucrose content in embryos doubled after 24 h of slow desiccation and more than tripled after 48 h. Conversely, starch content was decreased by one half after 24 h and by three quarters after 48 h. Sucrose abundance and raffinose occurrence after 48 h of slow desiccation were congruent with complete tolerance to fast desiccation. The period of slow desiccation between 24 and 48 h also increased the content of a 24-kDa dehydrin and the appearance of a 42-kDa dehydrin. The relationship between partial water loss, sugars and dehydrins is discussed with respect to tolerance to fast desiccation in black spruce somatic embryos.
Journal Article↗
FTDC1/2, oocyte-specific cofactors of DNMT1 required for epigenetic regulation and embryonic development.
The unique epigenetic patterns during gametogenesis and embryonic development indicate the existence of specialized methylation machinery. In the present study, we describe the discovery of two oocyte-specific cofactors of DNA methyltransferase 1 (DNMT1), encoded by uncharacterized genes, ferritin domain containing 1 and 2 (Ftdc1 and Ftdc2). Genetic ablation of Ftdc1 or Ftdc2 causes midgestation defects and female infertility. FTDC1 or FTDC2 depletion induces the progressive loss of DNA methylation including imprinted regions in early embryos. This loss correlates with a marked reduction in DNMT1 protein due to increased degradation, likely via the ubiquitin-proteasome pathway. Mechanistically, we find that FTDC1, FTDC2 and DNMT1 form a complex by direct interactions, thereby stabilizing each other. Surprisingly, knockout of Ftdc1 or Ftdc2 displayed stronger DNA demethylation phenotypes and earlier embryonic lethality than the Dnmt1-null mutant, implying their unique functions. These data suggest that FTDC1/2 are crucial players specifically involved in maintaining genomic methylation during embryogenesis, offering new insights into the epigenetic control of mammalian development.
DNA (Cytosine-5-)-Methyltransferase 1↗
Kinematics of trophectoderm projections and locomotion in the peri-implantation hamster blastocyst.
The behavior of golden hamster blastocysts was studied in vitro by continuous time-lapse videomicrography and computer imaging, during and immediately following escape from the zona pellucida. This study revealed numerous small cytoplasmic trophectoderm projections (TEPs) approximately 18 microns long that penetrated the zona pellucida both radically and tangentially and appeared to be actively involved in zona escape in vitro. After escape from their zonae, some blastocysts moved across the culture dish by an endogenous means of locomotion, most likely involving activity of the small TEPs. Several hours after zona escape, embryos expressed large TEPs up to 46 microns long that moved in an undulating manner and showed rapid cycles of extension and retraction; the timing of their appearance suggested that these TEPs are normally involved in attachment to the uterine epithelium. Embryos fixed in utero, during the developmental interval between zona loss and embryo attachment, exhibited large TEPs similar in morphology to those expressed by cultured blastocysts. These observations document for the first time that mammalian blastocysts are capable of endogenous locomotion, confirm TEPs as components of normal blastocyst activity, reveal that there are two kinds of TEPs that differ temporally and morphologically, and extend earlier reports of TEP activity in guinea-pig embryos to the hamster.
Animals↗
Cytogenetic analysis of human blastocysts.
UNLABELLED: The human blastocyst is key to understanding the aetiology of constitutional chromosome abnormalities in our species. OBJECTIVES: To investigate the range and incidence of chromosome abnormalities in a large series of human blastocysts, using classic cytogenetic techniques. METHODS: Using thymidine, cell division is synchronized in spare five-to-eight-day-old human blastocysts generated by IVF. A simple acetic acid disaggregation step produces discrete metaphases for G-band analysis. Subsequent FISH analysis of both metaphase and interphase nuclei allows further exploration of an abnormality detected by G-banding, including the investigation of any mosaicism. RESULTS: A total of 438 blastocysts have been prepared. Where analysis was possible, 3% appeared polyploid (mainly tetraploid), 29% were diploid : tetraploid mosaics and 68% were uniformly diploid. Abnormalities observed include triploidy, trisomy 16, trisomy 2, trisomy for unidentifiable D-group chromosome, mosaic trisomy 3, and mosaic trisomy 3 and trisomy 7. CONCLUSION: Comparison of results with existing data from both first trimester pregnancies and cleavage stage embryos suggests significant loss of haploid and monosomic embryos, as well as loss of some trisomies, prior to the blastocyst stage. It appears that the general range and incidence of most main groups of constitutional abnormalities observed in the first trimester (including mosaic forms) are in place by the blastocyst stage.
Adult↗
Xwnt-8 and lithium can act upon either dorsal mesodermal or neurectodermal cells to cause a loss of forebrain in Xenopus embryos.
When Xenopus gastrulae are made to misexpress Xwnt-8, or are exposed to lithium ions, they develop with a loss of anterior structures. In the current study, we have characterized the neural defects produced by either Xwnt-8 or lithium and have examined potential cellular mechanisms underlying this anterior truncation. We find that the primary defect in embryos exposed to lithium at successively earlier stages during gastrulation is a progressive rostral to caudal deletion of the forebrain, while hindbrain and spinal regions of the CNS remain intact. Misexpression of Xwnt-8 during gastrulation produces an identical loss of forebrain. Our results demonstrate that lithium and Wnts can act upon either prospective neural ectodermal cells, or upon dorsal mesodermal cells, to cause a loss of anterior pattern. Specifically, ectodermal cells isolated from lithium- or Wnt-exposed embryos are unable to form anterior neural tissue in response to inductive signals from normal dorsal mesoderm. In addition, although dorsal mesodermal cells from lithium- or Wnt-exposed embryos are specified properly, and produce normal levels of the anterior neural inducing molecules noggin and chordin, they show a greatly reduced capacity to induce anterior neural tissue in conjugated ectoderm. Taken together, our results are consistent with a model in which Wnt- or lithium-mediated signals can induce either mesodermal or ectodermal cells to produce a dominant posteriorizing morphogen which respecifies anterior neural tissue as posterior.
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Comparison of pregnancy rates from transfer of fresh versus cooled, transported equine embryos.
Donor mares of mixed, light-horse breeds, maintained at Colorado State University, provided 104 embryos for immediate transfer (fresh embryos). One hundred and thirty-six additional embryos were collected on various breeding farms in the United States and were shipped to Colorado State University via commercial airlines (cooled embryos). Embryos were harvested 7 d after ovulation, graded, and either transferred into a mare immediately (<1 h) or placed in Ham's F-10 medium plus 10% fetal calf serum in an atmosphere of 5% CO2, 5% O2, 90% N2 and packaged in a passive cooling unit (Equitainer) for shipment to our laboratory. All embryos were measured and graded just prior to surgical transfer via flank incision into synchronized mares. Recipients had ovulated 1 or 2 d before (+1, +2), on the same day as (0), or 1, 2 or 3 d after (-1, -2, -3) the donor mare. Pregnancy of recipients was determined by ultrasonography on 12, 35, and 50 d after ovulation of the donor. Pregnancy rates at 12, 35, and 50 d were similar for fresh (74, 64, 61%) and cooled embryos (80, 67, 66%), respectively. Overall, embryo size affected (P<0.05) pregnancy rates at 12, 35 and 50 d. Embryos of Grade 1 (excellent) or 2 resulted in more pregnancies than those of Grade 3 or 4 (poor) embryos. Embryonic losses between 12 and 35 d or between 35 and 50 d were not altered (P>0.05) by treatment (fresh or cooled) nor by age of the donor mare (P>0.05), but embryonic losses between 12 and 35 d were greater (P<0.06) for embryos stored for >12 h (25%) versus those stored for <12 h (10%). The duration needed for shipment (<12 h or >12 h) of cooled embryos did not alter pregnancy rates at 12 d (P>0.05). Age of donor mare had no effect (P>0.05) upon pregnancy rates of cooled or fresh embryos transferred nor on embryo quality. In summary, equine embryos can be cooled to 5 degrees C and maintained in storage for up to 24 h without decreased fertility, compared with those of embryos transferred in <1 hour.
Journal Article↗
Effects of mating dynamics and crowding on sex ratio variance in mice.
Mating units of six virgin females and one adult stud male were established to test for the effects of timing of mating and crowding of pregnant females on litter sex ratios in mice. Females either copulated during periods when no other female of the mating unit copulated simultaneously (single mating condition) or when more than one female copulated (multiple matings condition). Two crowding conditions were imposed on the animals: the females of 14 mating units were placed into individual cages after mating (isolated condition), while females of the other 13 mating units remained in the original group until shortly before littering (crowded condition). Sex ratio variance did not deviate from random expectation in litters arising from the multiple matings periods. However, in litters arising from single mating periods, extreme sex ratios were found significantly less frequently than expected by chance. Higher sex ratio variance in litters arising from multiple matings periods is attributed to the timing of mating being at higher variance under this condition, which is known to affect sex ratios in other rodents. Crowding significantly reduced sex ratio variance further. Reduced sex ratio variance under single mating and crowded conditions is speculated to follow from competition for resources between preimplantation embryos, which may be further increased by stressful effects of crowding. Loss of embryos after implantation appeared not to be responsible for the above effects.
Animals↗
Chromosome studies on early human embryos fertilized in vitro.
The majority of early spontaneous abortions carry a lethal chromosomal anomaly. While it is recognized that several factors would be responsible for some IVF failures, it is important to determine the contribution of chromosomal aberrations to the preimplantation loss of embryos produced in vitro. Chromosome analysis of embryos not destined for replacement in the uterus could help to elucidate this phenomenon of early embryonic loss. Fifty-five out of 239 embryos fertilized in vitro were successfully karyotyped and amongst these the overall rate of diploidy was 25.5% in this study, which mainly comprised rejected embryos. Embryos without cleavage had mostly a chromosomal defect (20/38) and only a minority (9/38) were unfertilized. Numerical abnormalities were found in a total of 33/46 (71.7%) morphologically normal embryos. In contrast a diploid chromosomal complement was found in only 11.1% (1/9) of morphologically abnormal embryos.
Blastocyst↗
Male excess among anatomically normal fetuses in spontaneous abortions.
Estimates of the sex ratio in miscarriages, obtained mainly by cytogenetic or nuclear sexing methods, have yielded conflicting results. We report the results of a study of the anatomic sex ratio among embryos and fetuses derived from a consecutive series of 3,469 miscarriages. The overall sex ratio (M:F) was 1.25. The male excess was confined to normally formed specimens (1.30) and was present at all gestational ages up to 23 weeks and all sizes over 5 cm. Among malformed specimens the sex ratio was close to unity (0.92). Agreement between chromosomal and anatomic sexing was excellent, and the cytogenetic sex ratio among anatomically normal abortuses showed a similar excess of males. We hypothesize that an excess of anatomic males among fetal deaths suggests the presence of a discrete cause or causes that operate on normally formed embryos and fetuses, whereas loss of malformed embryos and fetuses may be due to other mechanisms that affect females as often as males.
Abortion, Spontaneous↗
Continuous replication of Friend virus complex (spleen focus-forming virus-lymphatic leukemia-inducing virus) in mouse embryo fibroblasts. Retention of leukemogenicity and loss of immunosuppressive properties.
Exposure of NIH Swiss mouse embryo fibroblasts (MEF) to infectious Friend virus (FV) complex [containing defective spleen focus-forming virus (SFFV) and endogenous NB-tropic leukemia-inducing helper virus (LLV-F)] resulted in the productive infection of these cells by both SFFV and LLV-F. Stocks of SFFV derived after extensive growth in this Swiss MEF cell culture system are fully leukemogenic in adult mice for the induction of erythroleukemia and spleen foci. In addition, in vitro-derived LLV-F, when isolated free of SFFV, is fully leukemogenic for the induction of lymphatic leukemia when inoculated into susceptible newborn BALB/c mice. The host range of in vitro-derived FV complex (i.e., FV-TC) for focus formation in vivo is NB-tropic. Unlike in vivo-derived FV complex, FV-TC does not suppress the responsiveness of murine thymocytes to concanavalin A (Con A) in vitro. Rather, FV-TC acts as a mitogen to nonspecifically stimulate the proliferation of BALB/c thymocytes. The mitogenicity of in vitro-derived FV complex is directly associated with the presence of type-C virus particles, is a heat-labile and UV-sensitive property of the virus, and may be primarily due to LLV since equivalent amounts of LLV with or without SFFV present are equally mitogenic. One in vivo passage of FV-TC resulted in the total loss of this mitogenic property with the reappearance of full immunosuppressive properties. This result demonstrates a clear association between in vivo growth of FV and its ability to suppress mouse thymocytes, and suggests that FV complex (SFFV-LLV) is not inherently immunosuppressive for these cells. While the mechanism of this interconversion between immunostimulatory and fully suppressive virus is unknown, both virus markers appear to be dependent upon the presence of infectious FV.
Animals↗
[How high are the "normal" early embryonic losses, that is, preclinical and clinical abortions?].
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Abortion, Spontaneous↗
The maternal sex determination gene daughterless has zygotic activity necessary for the formation of peripheral neurons in Drosophila.
The daughterless (da) gene is known to have separate maternal and zygotic functions: Maternally supplied daughterless activity is required for proper sex determination and dosage compensation in female embryos, whereas loss of zygotically supplied da+ activity causes embryonic lethality in both male and female embryos. We have found that the zygotic da+ activity is necessary for neural development: The use of neuron-specific antibodies and beta-galactosidase-marked X chromosomes has revealed that in both male and female embryos deletions or strong mutations of the da gene remove all peripheral neurons and associated sensory structures without disrupting the epithelium from which they derive. Partial da+ function causes partial removal of peripheral neurons. Our results indicate that da+ is required for the formation of peripheral neurons and their associated sensory structures.
Animals↗
Combined activities of hedgehog signaling inhibitors regulate pancreas development.
Hedgehog signaling is known to regulate tissue morphogenesis and cell differentiation in a dose-dependent manner. Loss of Indian hedgehog (Ihh) results in reduction in pancreas size, indicating a requirement for hedgehog signaling during pancreas development. By contrast, ectopic expression of sonic hedgehog (Shh) inhibits pancreatic marker expression and results in transformation of pancreatic mesenchyme into duodenal mesoderm. These observations suggest that hedgehog signaling activity has to be regulated tightly to ensure proper pancreas development. We have analyzed the function of two hedgehog inhibitors, Hhip and patched 1 (Ptch), during pancreas formation. Our results indicated that loss of Hhip results in increased hedgehog signaling within the pancreas anlage. Pancreas morphogenesis, islet formation and endocrine cell proliferation is impaired in Hhip mutant embryos. Additional loss of one Ptch allele in Hhip-/-Ptch+/- embryos further impairs pancreatic growth and endodermal cell differentiation. These results demonstrate combined requirements for Hhip and Ptch during pancreas development and point to a dose-dependent response to hedgehog signaling within pancreatic tissue. Reduction of Fgf10 expression in Hhip homozygous mutants suggests that at least some of the observed phenotypes result from hedgehog-mediated inhibition of Fgf signaling at early stages.
Animals↗
[A trial of histological preparation of early mouse embryos with the Technovit 7100 system].
A reproducible procedure was devised for making histological preparations of early mouse embryos cultured in vitro. This method was characterized by use of a resinous embedding material, Technovit 7100, and a 96-well U-bottomed microplate, which enabled efficient rinsing and dehydration of fixed embryos without loss. Technovit 7100 polymerized or hardened at room temperature slowly enough to allow sedimentation of embryos to the bottom, which enabled more correct prediction of the place of the embryos at sectioning. The present method will lead to easier microscopic observation of early embryos in embryology.
Animals↗