EMBO Fellows Meeting 2012

Aldine Amiel
EMBO Fellows Meeting 2012
Early development of the annelid polychaete Capitella teleta: new insights into the
organizing activity and axes establishment in lophotrochozoan
Abstract
Formation of body axes is a crucial biological process for successful animal development. In well-studied
metazoan model organisms such as Xenopus (Vertebrata), sea urchins (Echinodermata) and fruit flies
(Ecdysozoa), the formation of signaling center(s) during early embryogenesis is involved in establishment of
body axes. These signaling centers are composed of a specialized group of cells that induce the surrounding
cells, and orchestrate the formation of the organism via cell-cell signaling and morphogenetic movements
during embryogenesis. Lophotrochozoa, (i.e molluscs, annelids) are the third largest group of animals, and
although they display a high diversity of body forms, the embryology of this group is largely understudied. How
their diverse body forms emerged and how body axes are established remain important questions in this vast
group of animals. The currently available data from lophotrochozoans show the presence of an organizing
activity in one or two cells in the early cleavage stage embryo, namely 3D in the mollusks L. obsoleta, 4d in C.
fornicata, and 2d1 plus 4d in the oligochaete annelid T. tubifex. Molecular data describing the mechanisms
involved in organizing activity have been shown from only the mollusks, and are controversial. The identity of
an organizing activity has not yet been characterized in polychaetes. The purpose of the present study is to
investigate whether a similar organizing activity is present in the polychaete annelid Capitella teleta, an
emerging model organism well suited for embryological approaches. The stereotypic spiralian cleavage
program in Capitella and its known cell lineage allows identification of each cell and its resulting larval fate.
Over 12 uniquely identifiable individual blastomeres were deleted in Capitella using the XY clone laser deletion
system and resulting larval phenotypes analyzed. For many of the blastomere deletions, resulting larvae lacked
structures that normally arise from the deleted cell, but were otherwise normal. However, our results show
that an organizing activity in Capitella is necessary for the formation of the bilateral symmetry and the D/V axis
of the head and arises from one cell in the D quadrant. This cell possesses a different identity than in mollusks
(3D, 4d) or oligochaetes (2d1 plus 4d), and its activity occurs at an earlier stage of development. These results
highlight developmental variations among lophotrochozoans, and may ultimately give insight into the presence
of the high diversity of body forms in Lophotrochozoa and the evolution of the organizing activity during axes
establishment in Metazoa.
Aldine R. Amiel, Jonathan Q. Henry, and Elaine C. Seaver
14-17 June 2012, Heidelberg, Germany