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A K Tarkowski

Publications and source records attributed to A K Tarkowski.

At least 37 records · Page 2Linked to original sources
PubMed1984

Behaviour of thymocyte nuclei in non-activated and activated mouse oocytes.

Cells originating from the thymus of newborn mice were fused with mouse oocytes using polyethylene glycol. The behaviour of thymocyte nuclei was studied in non-activated metaphase II oocytes, and in oocytes activated in vitro with ethanol. In non-activated oocytes all thymocyte nuclei undergo premature chromosome condensation with individualization of chromosomes; the chromosomes form separate groups in the cytoplasm, or are assembled around the metaphase II spindle, or located on the extra-spindle. In activated oocytes thymocyte nuclei start to develop along a pronucleus-like pathway (decondensation, visualization of nucleoli, swelling) and increase up to 200 times in volume during 24 h culture in vitro, eventually reaching the size of a fully grown pronucleus. Activation/fusion timing seems to be critical for the full remodelling of thymocyte nuclei. Nuclei introduced before (10-30 min) or shortly after (up to 60 min) activation often grow larger than the female pronucleus. Those introduced into oocytes long before activation (greater than 30 min) undergo premature condensation with subsequent reformation of nuclei that are sometimes deficient (as indicated by the presence of micronuclei), or of hybrid character. Nuclei introduced late after activation (greater than 60 min) are mostly doomed to retarded development. The implications of the present observations for nuclear transfer experiments in mammals are discussed.

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PubMed1984

Autonomous cortical activity in mouse eggs controlled by a cytoplasmic clock.

Mouse eggs of Swiss albino origin, both parthenogenetic and fertilized, were bisected into nucleate (NHs) and anucleate halves (AHs) and observed in vitro (semicontinuous observations) for up to 40 h for possible manifestations of cortical activity. Three experimental groups were studied: (1) Non-fertilized eggs activated 17 h after administration of hCG with a heat-shock and bisected 4 h later. (2) Non-fertilized eggs first bisected, and the resulting sister halves activated 17 h after administration of hCG with ethyl alcohol. (3) In vivo fertilized eggs bisected 27 h after administration of hCG into an AH and a binucleate half. Parthenogenetic eggs (intact, zona-free, and incompletely bisected), and fertilized eggs collected 17, 20, and 27 h after administration of hCG were also studied. In the middle of the first cell cycle the cell surface in all types of cells studied changed from smooth to slightly undulate. In nucleate cells the surface deformations lasted for several hours and disappeared shortly before the first mitosis. In contrast, in AHs the indentations of the cell surface deepened, and developed into manifold furrows, thus leading to fragmentation. However, in 20% of AHs fragmentation was partially or completely reversed. The incidence and the intensity of fragmentation were lower, and its reversibility was more common in AHs carrying the 2nd polar body. We suggest that the interphase nucleus, i.e. the pronucleus in whole eggs and NHs, and the 2nd polar body nucleus (if 2nd polary body is attached to an AH) exerts a moderating effect on cortical activity. However, the initiation of cortical activity is nucleus-independent, as shown by the behaviour of AHs separated before activation. We believe that the observed phenomena reflect autonomous cortical activity which is regulated by a cytoplasmic clock.

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PubMed1982

A method for obtaining chimaeric mouse blastocysts with two separate inner cell masses: a preliminary report.

Pairs of zona-free mouse blastocysts aggregated in the presence of inactivated Sendai virus and subsequently cultured in vitro will fuse to form a chimaeric blastocyst with one common blastocoelic cavity. Depending on the relative position of the inner cell masses in the apposed 'parental' blastocysts, the resulting chimaeric blastocyst contains either a single inner cell mass (ICM) of dual origin or two discrete ICMs each originating from one embryo. In the present experiments, fusion between the two aggregated blastocysts occurred in 23% of the pairs and 64% of these chimaeric blastocysts contained two ICMs. Blastocysts of the latter type could potentially give rise to pairs of embryos which as regards the topography of the foetal membrane would resemble spontaneous identical twins, although they would be genetically dissimilar. Possible applications of the described method are discussed.

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PubMed1980

Nucleo-cytoplasmic interactions in cell hybrids between mouse oocytes, blastomeres and somatic cells.

With the help of the technique of Sendai virus-mediated cell fusion, hybrid cells were produced between two maturing oocytes, between maturing oocytes or mature secondary oocytes and interphase blastomeres from 2-cell embryos, and between secondary oocytes and follicle cells (FC). In the first case giant oocytes form and in these the two groups of condensing bivalents join on a common spindle, undergo a first meiotic division, and become arrested in metaphase II; these hybrids are heterozygous diploids. When blastomeres are fused with oocytes undergoing maturation, then the blastomere nucleus undergoes premature chromosome condensation (PCC), and two sets of chromosomes (meiotic and mitotic) come close to each other but the mitotic chromosomes are not fully incorporated into the meiotic spindle. The behaviour of the nuclei from blastomeres or from follicle cells fused with secondary ovulated oocytes, depends on whether or not the oocyte undergoes activation. When the oocyte is not activated, then the introduced nuclei undergo PCC but the chromosomes remain separate from the spindle of metaphase II. When the oocyte is activated, then the introduced nuclei remain in interphase; the FC nuclei may increase their volume eight times and undergo some other structural changes but during the 6 h period after fusion their appearance remains distinct from that of the female pronucleus. Since some oocytes are not activated after fusion has occurred, it follows that the fusion process itself is not sufficient to trigger egg activation.

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PubMed1976

Diploid parthenogenetic mouse embryos produced by heat-shock and Cytochalasin B.

Swiss albino and C57BL/10 eggs from induced ovulations, and spontaneously ovulated A eggs, were activated in vitro by a heat shock of 44 degrees C for 5 to 7-5 min and cultured in the presence of 10 mug/ml of Cytochalasin B (CB) for 5-8 h. The activation rate was about 70% in Swiss albino, 40% in C57BL and 90% in A eggs. CB suppressed second polar body (2P.B.) formation in over 90% of activated eggs, with the majority containing two pronuclei. When eggs were placed in CB-free medium their surface became wrinkled and they formed protrusions of various sizes, which in some eggs detached to form enucleate or pronucleate cytoplasmic fragments; some eggs broke down completely into fragments. In most eggs, however, the surface smoothed out in a few hours and suppression of 2P.B. appeared to be permanent. The rate of development of these eggs after transplantation to the oviduct was delayed in terms both of cell divisions and of the time of blastocyst formation. Out of 41 implants collected on the 8th-10th day of pregnancy only two healthy looking egg-cylinders were found on the 8th and 9th day; both were retarded, at the stage characteristic for the 7th day of normal development. The reasons for delayed preimplantation development and low implantation rate are discussed. The present experiments corroborate earlier observations that parthenogenetic mouse embryos, even if diploid, rarely survive in the uterus beyond the egg-cylinder stage.

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