[25.] Voronina E, Lopez M, Juliano CE, Gustafson E, Song JL (2008) Vasa protein expression is restricted to the small
micromeres of the sea urchin, but is inducible in other lineages early in development.
As a rule, specification of 3D and formation of the mesentoblast occur as soon as the presumptive ectodermal
micromeres and endodermal macromeres have been separated.
In early development there is an apparent lack of a hyaline layer, irregularly arranged blastomeres, variable numbers of
micromeres, and an absence of primary mesenchyme (Schroeder, 1981).
Third cleavage leads to the formation of the first quartet of
micromeres located at the animal pole (1a-1d).
During cleavage, gastropod Hb-like expression is uniform and labels both
micromere and macromere nuclei (Fig.
In addition, an apical sensory organ, often associated with a tuft of long cilia, arises from cells generated from the 1st
micromere tier, and additional cells anterior to the mouth may bear short cilia.
For example, patellogastropods (true limpets) and euthyneuran gastropods (pulmonates and opisthobranchs) with equally cleaving eggs depend on regional segregation of morphogenetic determinants to specify the animal-vegetal axis (4), but an inductive interaction between
micromeres and one of the macromeres later specifies the dorsoventral axis of the embryo (5, 6).
Micromere differentiation in the sea urchin embryo: immunochemical characterization of primary mesenchyme cell-specific antigen and its biological roles.
In S2, there was a differentiation of vegetative (macromeres) and animal (
micromeres) poles, while the embryo was 49.5 [+ or -] 4.7 mm in diameter.
Su, et al., (1982) reported that both species Coptotermes heimi and
Micromeres obesi do not penetrate Permethrin treated soil.
Eight species (Chaenactis glabriuscula, Cryptantha
micromeres, C.
At this stage, the blastomeres divided unequally, creating cells of various sizes, including macromeres and
micromeres (Fig.