Characterization of bovine placental trophoblast giant cell migration by three-dimensional reconstruction

The bovine trophoblast giant cells (TGC) migrate towards the mater-nal epithelium to deliver hormonal products to the maternal com-partment. To do so, TGC forms pseudopodia towards the maternal epithelium. Since the literature contains little work about the actual migration dynamics, the aim of the study was to analyse TGC mi-gration three-dimensionally by serial block face scanning electron microscopy (SBF-SEM). Placenta samples from eight cows (gestation days 120, 150, 177, 205, 266, 270, 278 and 284) were collected, fix-ated in Karnovsky and embedded in Durcupan. Stacks, each of 3000 sections (60 nm thickness), were created by SBF-SEM. Analyses, il-lustrations and model presentations were done with the software Microscopy Image Browser and IMOD. Volume calculations were performed with the software Amira. Transmission electronic micros-copy images were generated for further details. Pseudopodia were observed in both, the TGC's rear end closely associated with the foetal basement membrane and the migration front making contact with the uterine epithelium. They contained pale organelle with poor fluid and were in contact with the cell through openings of vary-ing sizes. Pseudopodia were observed in all stacks examined. One TGC could have up to four pseudopodia. The volume of pseudopo-dia varied between 50 and 2000 μm3. As part of the work, the term ‘pale bleb-like pseudopodium’ was elaborated. In theory, increased hydrostatic pressure leads to the separation of the cell membrane from the actin cortex, which allows ‘pale’ cytosol to flow in. Then, the actin cortex is degraded and organelle-rich parts can enter.