Similarly in mollusks the stem cell of the mesentoblast (macromere
3D) and its daughter cell (mesentoblast 4d) act as organizers and specify the developmental fate of a large number of blastomeres (Damen 1994, Damen and Dictus 1994a,b).
cell fates during sea urchin development.
In equal-cleaving embryos without polar lobes the dorsal (D) cell quadrant is determined later during development by virtue of cell-cell inductive interactions between derivatives of the first quartet micromeres (la1-Id") and one of the vegetal macromeres
(presumptive 3D macromere
) after the birth of the third quartet (van den Biggelaar and Guerrier, 1979; Arnolds et al., 1983; Martindale et al, 1985; Kuhtreiber et al., 1988; Boring, 1989; van den Biggelaar, 1996; Henry, 2002).
obsoleta Hb-like proteins are expressed in every micromere and macromere
nucleus from one cell to at least the sixth cleavage division.
During second cleavage, the macromere
with most of the red cytoplasm failed to separate completely at its vegetal pole (Fig.
Classical experiments performed on gastropod embryos demonstrate that the D macromere
plays a critical role in axial patterning as the founder cell of the dorsal lineage.
It is not clear how morphogenesis of the rest of the gut (e.g., mouth and stomodaeum) might be affected by macromere
ablation, but it is possible that a simple reduction of endodermal cell volume might permit the development of a complete larval gut.
At this stage, the embryo is designated a morula, and the uniformly distributed pigment granules become unevenly distributed to specific cells, with most going to the 8 macromere
3D) and gave rise to micromeres and macromeres
. The cleavage was total and spiraled, and no polar lobes were observed.
Asi, reconocen las series Macromeres
, Aulacothelae y Glanduliferae.
rosaceus follows the typical pattern for echinoids with planktotrophic larvae, beginning with three equal cleavages followed by the formation of mesomeres, macromeres
, and micromeres at the 16-cell stage (Fig.