Mammalian chimaeras / Anne McLaren.

  • McLaren, Anne.
Date:
[1976]
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Mammalian chimaeras / Anne McLaren. Source: Wellcome Collection.

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    Injection chimaeras 31 The decidualized uterus is also characterized by binucleate cells and cells with up to sixty-four times the haploid amount of DNA. Electrophoretic analysis of GPI-1 types was therefore applied to chimaeric decidua on the 8th day of pregnancy (Ansell et al., 1974). Again no hybrid enzyme could be detected electrophoretically, indicating that the increase in DNA content was due to DNA replication without cell division, rather than to cell fusion. Injection chimaeras The injection of two to five cells from dissociated blastocysts of a pigmented genotype (CBA-T6T6 x PDE) into the cavity of blastocysts from an albino strain (PDE) resulted in overt chimaerism, both at mid-gestation and after birth (Gardner, 1968). The proportion of chimaeras was low (less than 20 %), but in those animals that were chimaeric the injected cells had made a sub¬ stantial contribution to the phenotype. At mid-gestation two foetuses showed strong pigmentation in the eye, and 15-20% of donor-type metaphases (T6T6); of the two chimaeras that survived to weaning, one showed extensive pigmentation of the coat and underlying skin, while the other (from a reci¬ procal transfer of albino cells into a pigmented blastocyst) showed only limited chimaerism. In a recent study (Ford et al. 19756), a further two adult chimaeras of the same type (CBA-T6T6 x PDE) ^ PDE, were analysed. Identification of the T6 marker chromosomes showed that the contribution of the donor cells was remarkably high in a number of different tissues, including bone marrow, thymus, Peyer's patches, spleen, lymph nodes, gut, cornea (left and right), ovaries, testes, blood, skin and kidney. The proportions of donor cells ranged from 9 % (bone marrow) to 91 % (cornea) in one animal, and from 6 % (testis) to 68 % (blood) in the other. Since the reciprocal strain combination has not been studied, it is difficult to know to what extent the high incidence of donor cells reflects a selective advantage on the part of the donor strain, leading for example to a higher rate of cell division, and to what extent it implies that the total number of cells in the blastocyst contributing descend¬ ants to the foetus is normally very low. The distribution of the donor cells will be discussed further in Chapter 10. The degree to which cells of a different developmental age can contribute to the embryo has been examined by Moustafa & Brinster (1972йг, b). When cells from embryos 0,4 and 8 days older were labelled with tritiated thymidine and injected into blastocysts, autoradiography revealed tht the donor cells were still detectable in the blastocysts after 40 hours' in-vitro culture, and indeed had increased somewhat in numbei. However, it seems that hetero- chronic cells are less likely to get incorporated in the developing embryo than are those of the same age. Use of a pigment marker showed that donor cells 0, 2, 4 and 8 days older than the recipient blastocysts gave rise