The morphological and functional ultrastructure of cells in pre-implantation embryos.

Cells of pre-implantation embryos are equipped with many morphological and functional systems through which they can synthesize specific proteins and effectively ensure the protection of early embryonic development. Here we present evidence for the existence of these systems in morphologically normal and abnormal bovine blastocyst stage embryos in vivo at the ultrastructural and actin cytoskeleton levels. The appearance of organelles in the trophectoderm (TE) and inner cell mass (ICM) cells, responsible for their synthetic activities and their role in the development of early bovine embryos are described. We point out the importance of endocytic processes and the participation of extracellular vesicles in the formation of intercellular contacts and homeostasis of the embryo microenvironment. Several changes in the ultrastructural morphology of embryos produced by different methods (ICSI, parthenogenetic AC/DC electrical activation, IVF with separated sperm) and freezing/thawed embryos are described. We also show alterations occurred in the organelles after viral contamination of embryos with BHV-1 and BVDV viruses, and in embryos from over-conditioned cows. Recorded changes in organelles and appearance of cellular autophagic structures (vesicles, multivesicular bodies and autophagolysosomes) may negatively affect embryo metabolism and lead to the emergence of pathological processes in TE and ICM cells of preimplantation embryos.