Properties of Cultured Preimplantation Mouse and Rabbitembryos, and Cell Strains Derived from Them. In: Wolstenholme GEW, O'connor M, editors. Ciba Foundation Symposium - Preimplantation Stages of Pregnancy. Chichester: John Wiley & Sons, Ltd.; 1965. pp. 82-122. [DOI: 10.1002/9780470719435.ch5]

Use of the Coelomic Grafting Technique for Prolonged ex utero Cultivation of Late Preprimitive Streak-Stage Rabbit Embryos

Due to its morphological similarity with the early human embryo, the pregastrulation-stage rabbit may represent an appropriate mammalian model for studying processes involved in early human development. The usability of mammalian embryos for experimental studies depends on the availability of whole embryo culture methods facilitating prolonged ex utero development. While currently used culture methods yield high success rates for embryos from primitive streak stages onward, the success rate of extended cultivation of preprimitive streak-stage mammalian embryos is low for all previously established methods and for all studied species. This limits the usability of preprimitive streak-stage rabbit embryos in experimental embryology. We have tested whether the extraembryonic coelom of 4-day-old chick embryos may be used for prolonged ex utero culture of preprimitive streak-stage rabbit embryos (stage 2, 6.2 days post coitum). We found that, within this environment, stage 2 rabbit blastocysts can be cultured at decreasing success rates (55% after 1 day, 35% after 2 days, 15% after 3 days) up to a maximum of 72 h. Grafted blastocysts can continue development from the onset of gastrulation to early organogenesis and thereby form all structures characterizing age-matched controls (e.g. neural tube, somites, beating heart). Compared to normal controls, successfully cultured embryos developed at a slower rate and finally showed some structural and gross morphological anomalies. The method presented here was originally developed for whole embryo culture of mouse embryos by Gluecksohn-Schoenheimer in 1941. It is a simple and inexpensive method that may represent a useful extension to presently available ex utero culture systems for rabbit embryos.

Stem cells today: A. Origin and potential of embryo stem cells

The study of embryo stem cells began in 1963, initially using disaggregates of cleaving rabbit and mouse embryos. Their differentiation in vitro was modest, and usually curtailed at best to the formation of trophectoderm cells, which attached to plastic. Rabbit morulae and blastocysts adhered more readily, trophectoderm forming a sheet of cells which was overgrown by stem cells from inner cell mass. Whole-blastocyst cultures on collagen-coated surfaces produced a pile of cells, and its outgrowths included neural, blood, neuronal, phagocytic and many other types of cell. When inner cell mass was freed and cultured intact or as cell disaggregates, lines of embryo stem cells (ES) were established which possessed good rates of cleavage, and immense stability in their secretion of enzymes, morphology and chromosomal complement. Developmental capacities of single mouse embryo stem cells were measured by injecting one or more into a recipient blastocyst, and extent of colonization in resulting chimaeras measured their pluripotency. In mouse, cell clumps were termed embryoid bodies, which produced similar outgrowths as in rabbit. Component cells again differentiated widely, depending to a limited extent on their exposure to various cytokines or substrates. Markers for differentiation or pluripotency were established, which revealed how neural, cardiac, haematological and other ES lines could be established in vitro. These have proved useful to study early differentiation and their use in grafting to sick recipients. Displaying similar properties, human ES cells emerged in the late 1990s. Models for the clinical use of ES cells showed how they colonized rapidly, travelled to target tissues via fetal pathways, differentiated and colonized target organs. No signs of inflammation or tissue damage were noted; injured tissues could be repaired including remyelination, and no cancers were formed. ES cells offer wide therapeutic potentials for humans, although extensive clinical trials are still awaited.

The chromosomes of giant trophoblast cells of the mouse

Treatment of mouse trophoblast cells with actinomycin D causes the nuclear contents to condense into discrete bodies. A similar effect is observed when the antibiotic is applied to diploid or tetraploid blastocyst cells and in these cases the number of condensed bodies produced correlates closely to the known chromosome number. It is therefore argued that these bodies represent chromosomes. In the highly DNA-enriched trophoblast nuclei the number of these chromosomes generally does not exceed 40, the diploid number for mouse, indicating a considerable degree of polyteny in these cell nuclei.