Evolutionary implications of the mode of D quadrant specification in coelomates with spiral cleavage
Our recent research has focused on the development of two cell lines typical of the Spiralia (i.e., phyla with spiral cleavage
): (1) the stem cell of the mesodermal bands (the mesentoblast) and (2) the trochoblasts.
, which characterizes the embryos of phyla belonging to the Spiralia, typically involves the generation of four quartets of micromeres from the four macromeres produced by the first and second cleavages.
In particular, remarkable similarities in their embryonic cleavage pattern (spiral cleavage
) and cell lineages have been observed (1, 2).
These animals share many common features of embryonic development including a stereotypic pattern of cell divisions referred to as spiral cleavage
. In most molluscs and annelids, first cleavage occurs oblique to the future plane of bilateral symmetry and generates two blastomeres, designated AB and CD.