Micromeres


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Micromeres

 

the small cells that form by complete unequal cleavage of an ovum. Micromeres differ from the macromeres of the same embryo by their smaller size and yolk content. The micromeres are usually found in the animal hemisphere of the embryo (for example, in frogs), although sometimes they are located in the vegetal hemisphere (in sea urchins).

References in periodicals archive ?
Juliano CE, Voronina E, Stack C, Aldrich M, Cameron AR (2006) Germ line determinants are not localized early in sea urchin development, but do accumulate in the small micromere lineage.
When the ectodermal micromeres divide faster than the macromeres, then 3D induction and mesentoblast formation occur at a more advanced cell stage.
The first mesenchyme cells to ingress are called primary mesenchyme and are derived from the small micromeres that arise at the vegetal pole of the embryo during an unequal fourth cleavage.
The first two cleavages were equal and the third unequal, producing four micromeres and four macromeres at the animal and vegetal poles, respectively (Fig.
Third cleavage leads to the formation of the first quartet of micromeres located at the animal pole (1a-1d).
2] cells, which themselves are the vegetal daughters of the first quartet of micromeres formed at third cleavage).
Feeding veligers acquire a metatroch and food groove, which in Crepidula fornicata originate from progeny of a group of 2nd tier micromeres (Hejnol et al.
AmqNK2/3/4 transcripts are first detected during cleavage in a small number of micromeres per embryo (Fig.
How the genome changed the identification of network genes is well illustrated by the recent identification of HesC as the Repressor of Micromeres (Revilla-i-Domingo et al.
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).
Spicules of the sea urchin embryo are synthesized by primary mesenchyme cells (PMCs), which are descendants of the micromeres of the 16-cell-stage embryo (Gustafson and Wolpert, 1967; Okazaki, 1975; Ettensohn et al.
Recently, MAP kinase (MAPK) signaling cascades in the gastropod Ilyanassa obsoleta have been linked to cell fate specification within the D macromere lineage and the micromeres of the A, B, and C quadrants (Lambert and Nagy, 2001).