Search PubMed⌕ Search

Biomedical subjects

G A Wray

Publications and source records attributed to G A Wray.

24 records · Page 2Linked to original sources
PubMed1990

The dorsoventral axis is specified prior to first cleavage in the direct developing sea urchin Heliocidaris erythrogramma.

Previous fate mapping studies as well as the culture of isolated blastomeres have revealed that the dorsoventral axis is specified as early as the 2-cell stage in the embryos of the direct developing echinoid, Heliocidaris erythrogramma. Normally, the first cleavage plane includes the animal-vegetal axis and bisects the embryo between future dorsal and ventral halves. Experiments were performed to establish whether the dorsoventral axis is set up prior to the first cleavage division in H. erythrogramma. Eggs were elongated and fertilized in silicone tubes of a small diameter in order to orient the cleavage spindle and thus the first plane of cell division. Following first cleavage, one of the two resulting blastomeres was then microinjected with a fluorescent cell lineage tracer dye. Fate maps were made after culturing these embryos to larval stages. The results indicate that the first cleavage division can be made to occur at virtually any angle relative to the animal-vegetal and dorsoventral axes. Therefore, the dorsoventral axis is specified prior to first cleavage. We argue that this axis resides in the unfertilized oocyte rather than being set up as a consequence of fertilization.

Animals↗
PubMed1989

Early inductive interactions are involved in restricting cell fates of mesomeres in sea urchin embryos.

Isolated intact caps of animal blastomeres, obtained from either 8- or 16-cell embryos, differentiate as swollen ectodermal vesicles. These findings agree with earlier studies demonstrating that mesomeres contribute only to larval ectoderm during normal development. In contrast, we find that pairs of mesomeres isolated from 16-cell embryos can differentiate endodermal and mesenchymal cells in a substantial number of cases (23%). Thus, mesomeres have a greater developmental potential than is realized during normal development. Further results support hypotheses that graded distributions of morphogenetic determinants exist within these embryos, since the extent of differentiation of isolated mesomeres is related to the relative position of the third cleavage plane along the animal-vegetal axis. When the third cleavage plane is subequatorial and the resulting animal blastomeres inherit a fraction of the vegetal hemisphere, more cases (39%) differentiate endodermal and mesenchymal cell types. A significant number of mesomere pairs (9-14%), however, can still differentiate endodermal and mesenchymal cells when the mesomeres are formed within the animal hemisphere. Thus, putative vegetal morphogenetic determinants may extend into the animal hemisphere in some cases. Further results indicate a temporal restriction in the developmental potential of mesomeres or mesomere progenitor cells since their differentiative capability is greater if they are isolated earlier during development. Aggregates of isolated mesomere pairs also display a decreased developmental potential when compared to isolated mesomere pairs. These results suggest that associations with adjacent cells (vegetal cells as well as adjacent mesomeres) restrict the development of mesomeres between third and sixth cleavages.

Animals↗
PubMed1989

Evolutionary modification of cell lineage in the direct-developing sea urchin Heliocidaris erythrogramma.

The sea urchin Heliocidaris erythrogramma undergoes direct development, bypassing the usual echinoid pluteus larva. We present an analysis of cell lineage in H. erythrogramma as part of a definition of the mechanistic basis for this evolutionary change in developmental mode. Microinjection of fluoresceinated tracer dye and surface marking with vital dye are used to follow larval fates of 2-cell, 8-cell, and 16-cell blastomeres, and to examine axial specification. The animal-vegetal axis and adult dorsoventral axis are basically unmodified in H. erythrogramma. Animal cell fates are very similar to those of typically developing species; however, vegetal cell fates in H. erythrogramma are substantially altered. Radial differences exist among vegetal blastomere fates in the 8-cell embryo: dorsal vegetal blastomeres contribute proportionately more descendants to ectodermal and fewer to mesodermal fates, while ventral vegetal blastomeres have a complementary bias in fates. In addition, vegetal cell fates are more variable than in typical developers. There are no cells in H. erythrogramma with fates comparable to those of the micromeres and macromeres of typically developing echinoids. Instead, all vegetal cells in the 16-cell embryo can contribute progeny to ectoderm and gut. Alterations have thus arisen in cleavage patterns and timing of cell lineage partitioning during the evolution of direct development in H. erythrogramma.

Animals↗
PubMed1988

The origin of spicule-forming cells in a 'primitive' sea urchin (Eucidaris tribuloides) which appears to lack primary mesenchyme cells.

The calcareous larval skeleton of euechinoid sea urchins is synthesized by primary mesenchyme cells which ingress prior to gastrulation. In embryos of the cidaroid sea urchin Eucidaris tribuloides, no mesenchyme cells ingress before gastrulation, yet larvae later contain skeletons. This apparent paradox is resolved by immunochemical, cell lineage and morphological evidence showing that spicule-forming cells of Eucidaris are homologous to primary mesenchyme cells of euechinoids. In particular, these two cell types share expression of two cell lineage-specific gene products, are derived from the same cellular precursors, the micromeres, and undergo a similar migratory phase prior to skeletogenesis. Despite these similarities, there are far fewer spicule-forming cells in Eucidaris than in typical euechinoids and they assume a different pattern during spiculogenesis. The homology between Eucidaris spicule-forming cells and euechinoid primary mesenchyme cells indicates that a heterochrony in the time of spicule-forming cell ingression has occurred since the divergence of their respective lineages.

Animals↗