The unfertilized ascidian egg displays a visible polar organization along its animal-vegetal axis. In particular, the myoplasm, a mitochondria-rich subcortical domain inherited by the blastomeres that differentiate into muscle cells, is mainly situated in the vegetal hemisphere. We show that, in the unfertilized egg, this vegetal domain is enriched in actin and microfilaments and excludes micro...

We performed some experiments to investigate the temporal and spatial details of the dorsal induction exerted by dorsal vegetal cells in Xenopus embryo. Two dorsal vegetal cells (D1 cells) were transplanted into the ventral vegetal region of a recipient at the 32-cell stage. At various times after transplantation, the ventral animal-equatorial part was explanted and cultured. The explants isola...

J TORRA*, A CIRUJEDA , J RECASENS*, A TABERNER* & S B POWLES§ *Departament d Hortofructicultura, Botànica i Jardineria, ETSEA, Universitat de Lleida, Lleida, Spain, Unidad de Sanidad Vegetal, CITA, Diputación General de Aragón, Zaragoza, Spain, Servei de Sanitat Vegetal, Unitat de Malherbologia, Departament d Agricultura, Ramaderia i Pesca, Generalitat de Catalunya, Lleida, Spain, and §Western ...

Specification of the dorsoventral axis is a subject of great importance in amphibian embryogenesis. We have found that cytoplasm of the vegetal dorsal cells of a 16-cell embryo of Xenopus laevis, when injected into the ventral vegetal cells of a recipient at the same stage, can induce formation of a second axis. In the present experiments,using the same assay procedure, we found that the cytopl...

Gastrulation is the morphogenetic process by which, in metazoans, the germ layers are established in their characteristic spatial arrangement: ectoderm on the outside, endoderm inside, and mesoderm, if present, in between these two layers. Most often, the main activity of gastrulation involves the movement of the endoderm and mesoderm from the surface of the embryo to the interior, and a variet...

During the period of mitosis, two surface contraction waves (SCWs) progress from the animal to vegetal poles of the Xenopus egg. It has been shown that these SCWs occur in parallel with the activation of MPF and with its subsequent inactivation in the animal and vegetal hemispheres, suggesting that they are responses to propagated waves of MPF activity across the egg. We have analysed the mecha...

A main achievement of gastrulation is the movement of the endoderm and mesoderm from the surface of the embryo to the interior. Despite its fundamental importance, this internalization process is not well understood in amphibians. We show that in Xenopus, an active distortion of the vegetal cell mass, vegetal rotation, leads to a dramatic expansion of the blastocoel floor and a concomitant turn...

Aphidicolin, an inhibitor of DNA polymerase alpha, blocks DNA synthesis and cell division in sea urchin embryos. The effects of this inhibition appear to be stage dependent. Blastulae treated with aphidicolin before the thickening of the vegetal plate undergo developmental arrest prior to gastrulation. The extent of inhibition of DNA synthesis varies from 60 to 93% in these embryos. However, wh...

The developmental potential of different blastomeres of the sea urchin embryo was re-examined. We have employed a new method to isolate substantial numbers of different kinds of blastomeres from 16-cell-stage embryos, and we have used newly available molecular markers to analyze possible vegetal differentiation. We have found that, while isolated mesomere pairs behave according to the classical...

VegT is a T-box transcription factor whose mRNA is synthesized during oogenesis and localized in the vegetal hemisphere of the egg and early embryo. We show that maternally expressed VegT controls the pattern of primary germ layer specification in Xenopus embryos. Reduction of the maternal store completely alters the fates of different regions of the blastula so that animal cell fate is changed...