Christiane Daguzan

Lithium induces dorsal-type migration of mesodermal cells in the entire marginal zone of urodele amphibian embryos

SummaryThe effect of lithium (Li+) on gastrulation movements was investigated during the development of the urodele amphibianPleurodeles waltl. Attention was focused on mesodermal cell migration. Under conditions of Li+ treatment providing a maximal enhancement of dorsoanterior structures, it was found that the dorsoventral polarity of gastrulation was abolished. In particular, vital staining and scanning electron microscopy observations on embryo fractures showed that mesodermal cells migrated radially after Li+ treatment, which led to the formation of rounded embryos. Epiboly movements thus were accelerated. Nevertheless, contrasting with the precocious disappearance of the early-formed yolk plug, archenteron invagination was constantly retarded and commenced with a delay of several hours as compared to control gastrulae. Cell-lineage analysis of the progenies from ventral or dorsal equatorial blastomeres of 32-cell-stage embryos provided evidence that both dorsal and ventral mesoderm contributed to notochordal tissue after Li+ treatment. Dorsalization of the entire marginal zone was confirmed by the ability of the entire mesoderm rudiment to behave as a dorsal organiser after Li+ treatment. Comparison of the migratory behaviour of isolated animal hemispheres from Li+-treated or control embryos cultured on fibronectin-coated substrate indicated that all marginal cells acquired the autonomous capacity for migration of dorsal marginal cells under the action of lithium.

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.