Variation in ultrastructure of mucoid coat and shell membrane secretion of a dasyurid marsupial

In the dasyurid marsupial Sminthopsis crassicaudata, the shell membrane of cleaving embryos has a compact granular structure but becomes fibrous around blastocysts. Polyclonal antibodies were raised against the extracellular coats, mucoid and shell membrane, of oocytes and early embryos, Immunogold cytochemistry resulted in labelling of secretory granules in the epithelia of both the ampulla and isthmus of the oviduct, although the secretory granules of these two regions differed in their ultrastructural appearance. Those in the ampulla were heterogeneous with areas of varying electron density, whereas those in the isthmus were electron dense and homogeneous. Shell membrane precursors were found in secretory granules in the epithelia of the uterotubal junction and endometrial glands and were electron lucent.