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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    The statistical approach 113 organ. For example, AKR cells combined with those of other strains tend to predominate in all tissues except melanocytes and germ cells, and to con¬ stitute the overwhelming majority in lymphomyeloid tissues, whether ex¬ amined cytogenetically (Ford et al., 1974) or by enzyme determinations and serum allotypes (Barnes, Tuifrey, Drury & Catty, \91Щ. In C3H<->C57BL chimaeras the two strains tend to have approximately equal representation in the kidney, the C3H component predominates in liver and mammary gland, while the C57BL component appears to be at a selective advantage in erythropoietic tissue and gamma-globulin-producing cells - hence the concept of Sam, the Statistical Allophenic Mouse (Mintz, 1970é'), each of whose tissues has the most likely composition for the given strain combination. Without prior knowledge of the appropriate Sam's properties, the binomial approach is likely to fall into serious error. Rapidly dividing tissues should show the effects of cell selection particularly clearly. If cell division continues into postnatal life, as in spermatogenesis and haematopoiesis, a change with age in the balance of the two components may be seen. Evidence for temporal shifts in germ cell and erythrocyte popu¬ lations is cited in Chapters 4 and 7 respectively. A more elaborate (though related) statistical approach examines the com¬ parison between the proportions of the two chimaera components in different cell populations within an individual. Correlation analyses are used to esti¬ mate whether the two cell populations are independent, or are members of a single, larger population. The overall picture that emerges from these studies is of successive sampling events, with gradual restriction of developmental potential. Granulocytes and erythrocytes appear to derive from a common pool of stem cells at the time of X-inactivation; lymphocytes derive from different precursors (Gandini et ai, 1968), but with a common ancestral cell pool at an earlier stage (Mintz, 19716), producing a correlation between the relative proportions of the two haemoglobin and the two gamma-globulin types in chimaeras (Mintz & Palm, 1969; Wegmann & Gilman, 1970). Within the lymphomyeloid system, cells of the bone marrow, thymus and Peyer's patches seem to belong to one population and spleen and lymph node cells to another (Ford et al. 19756); both populations seem to derive from a single cell pool earlier in development (Gornish et ai, 1972). The lymphomyeloid system as a whole (Ford et al, 1974) shows some correlation with the melanocyte population, judged by coat colour, which in turn is positively correlated with the expression of the two components in the skeletal system (Grüneberg & McLaren, 1972). The most comprehensive application of such covariance analysis has been made, not on chimaeras but on X-inactivation mosaics (see Chapter 9), by Nesbitt (1971). In a variety of tissues of mice heterozygous for Cattanach's X-autosome translocation she examined the proportion of cells that had the translocated X chromosome inactive rather than the normal one. Dif-