| dc.description.abstract |
The development of Antechinus stuartiifrom the 2-cellstage to the blastocyst stage in vivo was examined byroutine transmission electron microscopy. The 2-8-cell stages had asimilar organization of organelles, whereas the 16- to 32-cell stages hadpluriblast cells and trophoblast cells forming an epithelium closely apposedto the zona pellucida. Specialized cell-zona plugs were formed at the8-cell stage, and primitive cell junctions appeared in later conceptuses. Thecytoplasmic organelles included mitochondria, lysosomes, aggregates of smoothendoplasmic reticulum, lipid and protein yolk bodies and fibrillar arrays,possibly contractile in function. Nuclei had uniformly-dispersed densechromatin. Nucleoli of 2-4-cell conceptuses were dense, compact andfibrillar, and those of 8-cell conceptuses and later conceptuses were finelygranular and became progressively reticulated. The embryonic genome isprobably not switched on before the 8-cell stage. Sperm tails were detected incells in several early conceptuses. The yolk mass had the same organelles ascells. Centrioles were discovered for the first time in marsupial conceptuses.These were prominently situated at a spindle pole in a 32-cell blastomere andwere associated with a nucleus and sperm tail at the 4-cell stage. It is verylikely that the paternal centrosome is inherited at fertilization andperpetuated in Antechinus embryos during cleavage. |
|