Figure 1: Localization of Na+, K+-ATPase activity following progesterone-induced maturation of stage-VI Xenopus oocytes. We see slight up-regulation (A) and then immediate complete downregulation of Na+, K+-ATPase activity (B-H). A: An up-regulation of Na+, K+-ATPase activity within 1 hr after progesteroneinduction. B: A substantial and near complete down-regulation of Na+, K+-ATPase activity following 3 hr of progesterone induction. C: Complete absence of Na+, K+-ATPase activity over the vegetal hemisphere. (D, E) Presence of vesicle associated reaction deposits in the sub cortical region of the oocyte following 3 hr of progesterone induction, suggesting endocytotic removal of the membrane Na+, K+-ATPase molecules from the plasma membrane. G: Presence of countable number of Na+, K+-ATPase molecules over the animal pole region of polar body extrusion following GVBD. Na+, K+-ATPase activity is completely down-regulated by GVBD, and vesicle-associated reaction deposits are absent from the cytoplasm of subcortical region. We believe the side that has maximum ATPase activity forms the dorsal side of the fertilized egg. This observation was only made possible by EM enzyme Histocytochemical technique: (I) Complete absence of reaction deposits, when K+ is completely removed. (F, J) Complete absence and near complete absence of Na+, K+-ATPase activity over two different regions over the animal hemisphere in the presence of 10 μM Ouabain. (H) The presence of countable number of Ca2+, Mg2+- ATPase activity at the region of polar body extrusion over animal pole region following GVBD. Magnifications/bar sizes: (A) 15,000/1 mm; (B) 6,000/1 mm; (C) 5,000/1 mm; (D) 5,000/100 nm; (E) 30,000/1 mm; (F) 15,000/1 mm; (G-I) 10,000/1 mm; (J) 8,000/1 mm. (Adopted from Mohanty and Gupta, 2012).