Pluriblast

The pluriblast is a pluripotent population of cells in the early mammalian conceptus that is distinct from the trophoblast, and gives rise to the germ layers of the embryo proper, as well as extraembryonic endoderm and extraembryonic mesoderm. Both the pluriblast and trophoblast arise from the totipotent cells of the early conceptus. By definition, the pluriblast does not give rise to trophoblast cells during normal development, although it may retain this potential under experimental conditions.

In most eutherian mammals the pluriblast is termed the inner cell mass, as it forms a mass of cells within the fluid-filled blastocyst, bounded by the trophoblast. However in metatherian (marsupial) mammals, and indeed in a small number of eutherian mammals, the pluriblast forms part of the blastocyst wall and no structure exists that can be described as an inner cell mass. "Inner cell mass" is thus a morphological term peculiar to the majority of eutherian mammals, whereas "pluriblast" is a functional term more widely applicable to conserved aspects of mammalian development.

References

* Johnson MH and Selwood L (1996). Nomenclature of early development in mammals. Reproduction, Fertility and Development. 8:759-764.