Fig. 9. Gestational ontogeny of hypoxia activation of the invasive endovascular trophoblast cell lineage.

Maternal hypoxia exposure (equivalent to 11% oxygen) was initiated on gestation day 6.5 (panels B and C), day 8.5 (panels E and F), day 10.5 (panels H and I), or day 11.5 (panels K and L) and continued until day 13.5 of gestation when animals were sacrificed. Gestationally matched pair-fed rats exposed to ambient conditions were used as controls (panels A, D, G, and J). Invasive trophoblast cells were monitored by cytokeratin immunostaining. Panels C, F, I, and L are high magnifications of areas highlighted in the boxes shown in panels B, E, H, and K, respectively. Chromogen: AEC; counterstain: hematoxylin; scale bars: panels A, B, D, E, G, H, J and K = 0.5 mm; panels C, F, I, and L = 0.25 mm. Panel M, quantification of the depth of cytokeratin positive cell penetration into the uterine mesometrial vasculature. Values are means ± the standard error of each mean (n=5 for all groups except day 8.5 to day 13.5, normoxia, n=7 and day 8.5 to day 13.5, hypoxia, n=6). The asterisks indicate a significant difference between pair-fed normoxia controls and maternal hypoxia exposed placentation sites (day 6.5 to day 13.5, P<0.0001; day 8.5 to day 13.5, P<0.04). Abbreviations: PF-N, pair-fed normoxia; HYP, maternal hypoxia; Invasion Index, see Materials and Methods or legend to Fig. 3. Please note that exposure to hypoxia from gestation day 6.5 to day 10.5 was critical to activation of endovascular trophoblast invasion.