Cultivation of Post-implantation Mouse and Rat Embryos on Plasma Clots.

INTRODUCTION D E S P I T E recent successes with the cultivation of mouse and rabbit eggs (references in Austin, 1961, pp. 144-7) techniques for the cultivation of post-implantation mammalian embryos have not hitherto advanced beyond those devised in the 1930's. Jolly & Lieure (1938) obtained development of rat and guinea-pig embryos explanted into homologous serum at stages between primitive streak and a few somites. They report that of their explanted rat embryos 37 per cent, developed an embryonic axis with a rhythmically beating heart, but only 9 per cent, a functioning circulation. None formed limb buds or a functioning allantoic circulation. Nicholas & Rudnick (1934, 1938) appear to have had a similar degree of success with rat embryos explanted into heparinized rat plasma and embryo extract. Waddington & Waterman (1933) explanted rabbit blastodiscs of primitive streak to 3-somite stages on to plasma clots; in the most successful cultures a 6-9 somite embryo was obtained with neural tube and beating heart, but without any blood circulation. These results are much inferior to those obtained with qhick embryos in vitro, and have only proved of very limited value for mammalian embryology. We therefore attempted to devise an improved technique. Preliminary trials with a variety of methods suggested that mouse embryos explanted on to plasma clots and grown in 5 per cent. CO2 were particularly promising. This method has now been tested thoroughly and found to give extensive development in a high proportion of explanted embryos of both the mouse and the rat. The following account describes the basic technique, a few modifications, and the percentages of explanted embryos that develop to different stages.