Because of the crucial significance of macromere
3D and mesentoblast 4d for the specification of the developmental fate of the embryonic cells, it may be assumed that heterochronic changes in 3D induction may have far reaching morphogenetic consequences.
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.
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.
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
becomes the mesentoblast precursor cell (5).
In a few cases we managed to destroy two adjacent M macromeres
, and one single E macromere
, and in most cases these formed tentacles.
Asi, reconocen las series Macromeres
, Aulacothelae y Glanduliferae.
6) M k Cladophoropsis macromeres
M a,c,e,k,m Taylor (6-8,14,17,25,35,40) C.