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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    Differentiation of ICM and trophectoderm 23 Table 2. The timing of development in the mouse* Days after Event fertilization 2-cell stage 8-celI stage Embryos enter uterus 3 Differentiation of trophectoderm and inner cell mass 3-3^ Blastocyst stage 3^ Implantation begins 4 Differentiation of primary endoderm and ectoderm 4-5 Appearance of proamniotic cavity 5^-6 Appearance of primitive streak 6^-7 Somite formation begins 8-8^ Formation of chorioallantoic placenta 9-10 X chrómosome inactivation not yet detectable, by genetic 4^ criteria X chromosome inactivation detectable, by late DNA 6-7 replication Primordial germ cells first seen, near base of allantois 7^-8 Primordial germ cells enter genital ridge 10^-11 Female germ cells commence meiosis 13-14 Melanoblasts leave neural crest 8^-9^ Haematopoiesis begins in yolk sac 8^-9 Haematopoiesis begins in foetal liver 9^-10 Haematopoiesis begins in foetal bone marrow 16-17 Birth 19-20 Days after birth Hairs erupt 6-7 Vaginal opening 28-35 Sexual maturity 35-42 * The times given are based on the randomly bred Q strain. Some inbred strains develop more slowly, with a total gestation period of up to 1 day more. in which three of the four embryos were reared to adulthood, descendants of each single blastomere were found distributed among most organs of the body. A similar result was obtained when pairs of 8-cell blastomeres were followed into post-implantation development, suggesting that totipotency continues at least until the 8-cell stage. Differentiation of inner cell mass and trophectoderm It seems that formation of the fluid-filled blastocyst involves the differentia¬ tion of a new tissue, the outer trophectoderm layer, whose properties (including the appearance of intercellular 'tight junctions') both allow the accumulation