Early embryogenesis has been examined experimentally in several echinoderm and hemichordate classes. Although these studies suggest that the mechanisms which underlie regional specification have been highly conserved within the echinoderm + hemichordate clade, nothing is known about these mechanisms in several other echinoderm classes, including the Ophiuroidea. In this study, early embryogenesis was examined in a very little studied animal, the ophiuroid Ophiopholis aculeata. In O. aculeata, the first two cleavage planes do not coincide with the animal-vegetal axis but rather form approximately 45° off this axis. A fate map of the early embryo was constructed using microinjected lineage tracers. Most significantly, this fate map indicates that there is a major segregation of ectodermal from endomesodermal fates at first cleavage. The distribution of developmental potential in the early embryo was also examined by isolating different regions of the early embryo and following these isolates though larval development. These analyses indicate that endomesodermal developmental potential segregates unequally at first, second, and third cleavage in O. aculeata. These results provide insight into the mechanisms of regional specification in O. aculeata and yield new material for the study of the evolution of echinoderm development.
Bibliographical noteFunding Information:
I thank Gary Freeman and Judy Lundelius for help in preparing the manuscript. In addition, I would like to thank Gary Freeman for his incessant technical and intellectual support. I also thank the FHL community and specifically George von Dassow and Richard Strathmann for technical help and thoughtful discussions. Finally, I thank Friday Harbor Laboratories and the Center for Cell Dynamics for the use of facilities necessary for this work. This work was supported by NSF grant IBN 9982024 to Gary Freeman.
- Blastomere isolation
- Early embryogenesis
- Fate map
- Regional specification