Fig. 4. An activated nuclear Smad2 pool is inherited through mitosis and persists for at least 4 hours. (A) The absolute increase in cell number, during the activin competence period, as a function of stage is depicted. (B) Nuclear Smad2 is relocalised to the nucleus after mitosis. Confocal microscopy observation, in real time, of GFP-Smad2 localisation in activin treated cells undergoing mitosis. The nuclear GFP-Smad2 concentration was quantitated and the values are shown on the right. (C) Transient activin treatment leads to the formation of a stable pool of phosphorylated Smad2. The experiment was designed as described in Fig. 3A. (D) GFP-Smad2 is localised in the nucleus for several hours after activin treatment. Dissociated animal cap cells from GFP-Smad2-injected embryos were treated with activin and loaded onto fibronectin substrates. The localisation of GFP-Smad2 was observed in the same cell, over a period of 4.5 hours, by confocal microscopy in real time. The quantitation of the nuclear GFP-Smad2 concentration is shown on the right. (E) Confocal microscopy observation, in real time, of GFP-Smad2 distribution in activin treated cells cultured on a fibronectin substrate. Yellow arrows indicate cells containing a small pool of GFP-Smad2, and red arrows cells with a bigger pool of GFP-Smad2.
