In Memoriam - Prof. Andrzej Krzysztof Tarkowski (1933-2016).

Professor Andrzej Krzysztof Tarkowski passed away last September (2016) at the age of 83. His findings, have become indispensable tools for immunological, genetic, and oncological studies, as well as for generating transgenic animals which are instrumental for studying gene function in living animals. His work and discoveries provided a tremendous input to the contemporary developmental biology of mammals.

Individual blastomeres of 16- and 32-cell mouse embryos are able to develop into foetuses and mice.

Cell and developmental studies have clarified how, by the time of implantation, the mouse embryo forms three primary cell lineages: epiblast (EPI), primitive endoderm (PE), and trophectoderm (TE). However, it still remains unknown when cells allocated to these three lineages become determined in their developmental fate. To address this question, we studied the developmental potential of single blastomeres derived from 16- and 32-cell stage embryos and supported by carrier, tetraploid blastomeres.

Blastomeres of the mouse embryo lose totipotency after the fifth cleavage division: expression of Cdx2 and Oct4 and developmental potential of inner and outer blastomeres of 16- and 32-cell embryos.

Sixteen inner or outer blastomeres from 16-cell embryos and 32 inner or outer blastomeres from 32-cell embryos (nascent blastocysts) were reaggregated and cultured in vitro. In 24 h old blastocysts developed from blastomeres derived from 16-cell embryos the expression of Cdx2 protein was upregulated in outer cells (new trophectoderm) of the inner cells-derived aggregates and downregulated in inner cells (new inner cell mass) of the external cells-derived aggregates. After transfer to pseudopregnant recipients blastocysts originating from both inner and outer blastomeres of 16-cell embryo developed into normal, fertile mice, but the implantation rate of embryos formed from inner cell aggregates was lower.

Mouse chimaeras developed from electrofused blastocysts: new evidence for developmental plasticity of the inner cell mass.

Blastocysts obtained from mice differing in pigmentation (albino versus pigmented) and the isoforms of glucose phosphate isomerase (GPI 1A versus 1B) were electrofused and those containing a single chimaeric inner cell mass (ICM) were transferred to the uterus of pseudopregnant recipients. The pups were recovered on the 20(th) day by Caesarian section and fostered by females that had littered on the previous night or 24 h earlier. Altogether nine adult animals and two pups, which died soon after delivery, were available for GPI analysis.

Identical triplets and twins developed from isolated blastomeres of 8- and 16-cell mouse embryos supported with tetraploid blastomeres.

We studied the developmental potential of single blastomeres from early cleavage mouse embryos. Eight- and sixteen-cell diploid mouse embryos were disaggregated and single blastomeres from eight-cell embryos or pairs of sister blastomeres from sixteen-cell embryos were aggregated with 4, 5 or 6 tetraploid blastomeres from 4-cell embryos. Each diploid donor embryo gave eight sister aggregates, which later were manipulated together as one group (set).

Experimentally produced diploid-triploid mouse chimaeras develop up to adulthood.

Spontaneous diploid-triploid chimaeras occur sporadically in various mammalian species including man, but so far have never been produced experimentally. In order to get a deeper insight into the developmental consequences of this anomaly, we have developed two procedures that enabled for the first time to produce routinely diploid-triploid embryos, foetuses, and animals in the mouse. These procedures are: (1) aggregation of cleaving diploid embryos with triploid embryos produced by suppression of the second polar body in zygotes, and (2) fusion of a haploid karyoplast with one blastomere of the two-cell diploid embryos.