Fig. 2. XCL100 phosphatase prevents both sperm chromatin decondensation in early embryos and nuclear accumulation of GFP-PCNA in embryos and Ca²⁺ ionophore-activated eggs. (A) Wide-field fluorescence microscopy of embryos microinjected with GFP-PCNA (control) and, in addition, with XCL100 (1.5 µM and 2.5 µM final concentration) before fertilization and imaged at 65 minutes after fertilization, just before NEB. XCL100 (2.5µM) blocked the cell cycle and NEB did not subsequently occur. Arrow indicates uncondensed sperm chromatin. (B) Nuclear GFP-PCNA fluorescence intensity (mean±s.e.m., control, n=6; 1.5 µM XCL100, n=3; 2.5 µM XCL100, n=4; 2.5 µM XCL100 unfertilized eggs, n=3) measured during the course of the cell cycle in the experiments shown in A. Five different females were used in experiments with embryos (graphs and bars) and three females in the experiments with unfertilized control eggs. Inset shows that 2.5 µM XCL100 prevented NEB. (C) Confocal images of nuclear GFP-PCNA in control (n=3) and XCL100-microinjected eggs (n=4) activated with A23187 (20 µM). The time-course of GFP-PCNA fluorescence intensity in the nucleus is also shown. NEB was not observed in the presence of XCL100. Scale bar: 50 µm.