Embryonic development in culture of two dasyurid marsupials, Sminthopsis crassicaudata (gould) and Sminthopsis macroura (spencer), during cleavage and blastocyst formation

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Abstract
Embryos of Sminthopsis crassicaudata and Sminthopsis macroura were cultured for up to 96 hours during cleavage and early expansion of the blastocyst in Dulbecco's modified Eagle's medium (DMEG), DMEG containing 2.76 gm/liter sodium lactate (DMEGL), DMEG containing 3.5 gm/liter galactose (DMEGAL), DMEG containing 15 ng/ml progesterone (DMEGP) or 150 ng/ml progesterone (DMEGP10), and DMEGL containing 15 ng/ml progesterone (DMEGLP). The disappearance of sperm was used to indicate the time of ovulation (day 0). Fertilized eggs were found in the uterus at the end of day 1, four-cell stages at the end of day 2, and embryos completing the fourth division by the end of day 3 in S. macroura and day 4 in S. crassicaudata. Estimated developmental times in culture were similar to those obtained in vivo. In both species, the first two divisions take about 24 hours, cleavage is arrested for 24 hours or longer at the rounded four-cell stage, and the third and fourth divisions take a further 24 hours. The blastocyst expands during the next 24 hours in which time the fifth and sixth divisions occur. It was possible to culture embryos from S. macroura but not S. crassicaudata over the four-cell stage to early expanding blastocysts. DMEGAL did not support cleavage in culture. DMEG, DMEGL, DMEGP, DMEGP10, and DMEGLP all supported culture during cleavage and early blastocyst expansion. Blastocyst expansion was slightly enhanced using media containing sodium lactate. More embryos completed the fifth division and formed expanding blastocysts in DMEG, DMEGL, and DMEGLP.