Meeting Abstract

91.6  Thursday, Jan. 7  A Secondary Embryonic Axis Induced by Transplanted D-quadrant Micromeres in an Oligochaete Annelid NAKAMOTO, A.*; SHIMIZU, T.; Univ. of Arizona; Hokkaido Univ. monaka@email.arizona.edu

In many animals, a specific region in the early embryo has a remarkable potential to act as an organizer. For example, the Spemann and Mangold’s organizer not only instructs ectodermal cells to differentiate into neural tissues but also induces the secondary axis when transplanted to the ectopic position of the host embryo. In the embryos which undergo spiral cleavage (e.g., mollusks and annelids), it has been known that the one blastomere at the four cell stage, called D-quadrant, plays an important role in axial pattern formation. In annelids, various embryological experiments have suggested that the D-quadrant functions as an organizer of embryonic axis. However, so far, this long-held view remains to be demonstrated directly. To address this issue, we carried out a series of D-quadrant micormere transplantation experiments in the oligochaete annelid Tubifex tubifex. When D-quadrant micromeres (2d and 4d) were transplanted to an ectopic position in an intact host embryo, the resulting chimeric recombinant embryo formed a secondary embryonic axis with duplicated heads and/or tails. Cell lineage analyses show that neuroectoderm and mesoderm along the secondary axis are derived from the transplanted D-quadrant micromeres and the endoderm along the secondary axis originates from the host embryo. These results show that D-quadrant micromeres of Tubifex have a capability to organize embryonic axis, indicating the potential homology to other metazoan organizers.