Meeting Abstract

87.1  Monday, Jan. 6 10:15  The Molecular Basis of the Leech O-P Equivalence Group and the Evovability of Metazoan Patterning Mechanisms KUO, D.-H.; National Taiwan University, Taipei, Taiwan dhkuo@ntu.edu.tw

The O-P equivalence group is a classical experimental paradigm in leech embryology. In leeches and their clitellate annelid allies, embryogenesis largely follows a stereotyped pattern of cell lineage. In these animals, segmental ectoderm and mesoderm arise from five bilateral pairs of teloblasts. Each teloblast undergoes repeated rounds of asymmetric cell divisions to produce a column of segmental founder cells (blast cells), each of which then follows a lineage-specific developmental pattern to give rise to a definitive set of differentiated pattern elements. Among the five pairs of teloblasts, the M teloblast primarily contributes to the mesoderm, and N, O/Ps, and Q to the ventral, lateral and dorsal ectoderm, respectively. Experimental evidences suggested that fate specification of the M, N and Q lineages occurs at the birth of each of these teloblasts and appears to be cell-autonomous. In contrast, the developmental potential of the O/P teloblasts is initially equivalent, and the specification of O and P fates only occurs later in the blast cells and depends on localized cell-cell interactions. Recent molecular analyses of the O-P equivalence group suggested that the patterning mechanism of this system is homologous to BMP-mediated dorsoventral patterning of neuroectoderm observed in many other metazoan species. However, the deployment and the effects of the BMP signal in the O-P equivalence group appear to have deviated significantly from the general model of BMP-mediated neuroectoderm dorsoventral patterning. Here, I will illustrate how these mechanistic differences can provide insights into the evolution of patterning mechanisms in metazoan embryonic development.