Time‐Lapse analysis and normal stages of development of cleavage and blastocyst formation in the marsupials the brown antechinus and the stripe‐faced dunnart

The first six normal stages of cleavage and blastocyst formation in vitro of the brown antechinus and the stripe-faced dunnart are described based on 429 embryos from 37 dunnarts and 143 embryos from 32 antechinus and an information from previous studies. Embryos were cultured in Dulbecco's modified Eagle's medium with high glucose and 10% foetal calf serum at 35 degrees C and 5% CO2 in air. Seven antechinus and 18 dunnart embryos were cultured in Rose chambers and filmed by time-lapse cinematography, with an exposure of 0.2 sec and at a rate of 1 frame/30 sec. A rim of zona was formed around the yolk mass during early cleavage. Blastomeres attached to this rim, ensuring that the zona in the hemisphere containing the yolk mass was the first to be lined by blastomeres during blastocyst formation, which is completed at about the 32-cell stage. Two foci were established during cleavage. The descendants of the first cell to divide at the four-cell stage included, at both the fourth and fifth division, the first cell to divide and the cell with the shortest cell cycle time and had the shortest average cell cycle time at each division. The descendants of the cell opposite the first cell to divide at the four-cell stage included, at both the fourth and fifth divisions, the last cell to divide and the cell with the longest cell cycle time and had the longest average cell cycle time at each division.