Differential Protein Distribution Related to Dorsoventral Polarity in Pleurodeles waltl Cleaving Egg

The molecular basis for the initial specification of dorsoventral polarity in the Amphibian egg prior to the mid‐blastula transition still remains an open question. Regional differences in the protein pattern of Pleurodeles egg were investigated during early cleavage (8‐ and 512‐cell stages, prior to the mid‐blastula transition). Animal‐dorsal, animal‐ventral, vegetal‐dorsal and vegetal‐ventral quarters were separated and proteins were analyzed by 2D‐electrophoresis. The comparison of acidic protein patterns from dorsal and ventral quarters revealed differences between vegetal cells but no difference was detected between animal cells. One protein (p11, 30 kDa) was characterized in the dorsal side as early as the 8‐cell st. and two dorsal spots were detected at the 512‐cell st. (p11 and p5, 65 kDa). Similarly one protein (p7b, 46 kDa) appears to be ventral‐specific from the 8‐cell st. The p11 spot was shown to appear in ventral cells as a consequence of a dorsalizing LiCl‐treatment at the 32‐cell stage. Conversely, p11 disappeared from dorsal cells and p5 did not appear at 512‐cell stage after UV‐irradiation of the uncleaved egg, which results in the expression of the ventral‐specific protein p7b in the dorsal part of the egg. Therefore differential protein expression is already present at very early cleavage stages. Its significance needs further investigation.