1,720,974 research outputs found
Amphibian and mammal somatic-cell cloning: different species, common results? (Cover page)
No full textGenome of non-living cells: trash or recycle?
No full textReproductive technologies have been often used as a tool in research not strictly connected with developmental biology. In this study, we retrace the experimental routes that have led to the adoption of two reproductive technologies, ICSI and somatic cell nuclear transfer (SCNT), as biological assays to probe the 'functionality' of the genome from dead cells. The structural peculiarities of the spermatozoa nucleus, namely its lower water content and its compact chromatin structure, have made it the preferred cell for these experiments. The studies, primarily focused on mice, have demonstrated an unexpected stability of the spermatozoa nuclei, which retained the capacity to form pronuclei once injected into the oocytes even after severe denaturing agents like acid treatment and high-temperature exposure. These findings inspired further research culminating in the production of mice after ICSI of lyophilized spermatozoa. The demonstrated non-equivalence between cell vitality and nuclear vitality in spermatozoa prompted analogous studies on somatic cells. Somatic cells were treated with the same physical stress applied to spermatozoa and were injected into enucleated sheep oocytes. Despite the presumptive fragile nuclear structure, nuclei from non-viable cells (heat treated) directed early and post-implantation embryonic development on nuclear transfer, resulting in normal offspring. Recently, lyophilized somatic cells used for nuclear transfer have developed into normal embryos. In summary, ICSI and SCNT have been useful tools to prove that alternative strategies for storing banks of non-viable cells are realistic. Finally, the potential application of freeze-dried spermatozoa and cells is also discussed.[...
GENETIC RESCUE OF AN ENDANGERED MAMMAL BY CROSS-SPECIES NUCLEAR TRANSFER USING POST-MORTEM SOMATIC CELLS.
No full textSince the advent of procedures for cloning animals, conservation biologists have proposed using this technology to preserve endangered mammals. Here we report the successful cloning of a wild endangered animal, Ovis orientalis musimon, using oocytes collected from a closely related, domesticated species, Ovis aries. We injected enucleated sheep oocytes with granulosa cells collected from two female mouflons found dead in the pasture. Blastocyst-stage cloned embryos transferred into sheep foster mothers established two pregnancies, one of which produced an apparently normal mouflon. Our findings support the use of cloning for the expansion of critically endangered populations.[...
Asymmetric nuclear reprogramming in somatic cell nuclear transfer?
No full textDespite the progress achieved over the last decade after the birth of the first cloned mammal, the efficiency of reproductive cloning remains invariably low. However, research aiming at the use of nuclear transfer for the production of patient-tailored stem cells for cell/tissue therapy is progressing rapidly. Yet, reproductive cloning has many potential implications for animal breeding, transgenic research and the conservation of endangered species. In this article we suggest that the changes in the epi-/genotype observed in cloned embryos arise from unbalanced nuclear reprogramming between parental chromosomes. It is probable that the oocyte reprogramming machinery, devised for resident chromosomes, cannot target the paternal alleles of somatic cells. We, therefore, suggest that a reasonable approach to balance this asymmetry in nuclear reprogramming might involve the transient expression in donor cells of chromatin remodelling proteins, which are physiologically expressed during spermatogenesis, in order to induce a male-specific chromatin organisation in the somatic cells before nuclear transfer.[...
Nucleus transfer in mammals: noninvasive approaches for the preparation of cytoplasts
No full textNucleus transfer in mammals:noninvasive approaches for thepreparation of cytoplastsJosef Fulka Jr1, Pasqualino Loi2, Helena Fulka1, Grazyna Ptak2 and Taku Nagai31Institute of Animal Production, POB 1, Prague 10, Czech Republic2University of Teramo, Department of Comparative Biomedical Sciences, Teramo 64100, Italy3National Institute of Livestock and Grassland Science, Tsukuba, Ibaraki 305-0901, JapanThe production of cloned animals is a difficult and complexprocedure that requires two basic steps. First, thecytoplast must be prepared by the enucleation of metaphaseII oocytes. Second, the nucleus is transferredeither by fusion or by direct microinjection into the cytoplast.The preparation of cytoplasts is a crucial stepbecause they must be able to reprogram the transferrednucleus and to secure the development of reconstructedembryos. Moreover, the classicalmechanical enucleationof metaphase II oocytes is rather technically difficult,requiring good equipment and considerable micromanipulationskill. For this reason the simplification of thisstep is permanently in the centre of interest of thosescientists who are involved in the production of clones.[...
Nucleus transfer in mammals: how the oocyte cytoplasm modifies the transferred nucleus
No full textSuccessful development of clones depends on the reprogramming of transferred nuclei in enucleated oocytes. Thus far, oocytes are the only cells that can convert nuclei, which are already differentiated, into undifferentiated stages resembling pronuclei in freshly fertilized zygotes and that can then complete development of the reconstructed embryos. However, we still don't know exactly how the enucleated oocyte (cytoplast) secures this reprogramming. Oocytes exhibit a number of cytoplasmic activities that may be involved reprogramming. We discuss how these activities may be involved in reprogramming of transferred nuclei. (C) 2001 by Elsevier Science Inc
- …
