Bruce M. Carlson

“Fig. 3.7 The cell polarity model of differentiation of blastomeres. A, If the plane of cleavage of a blastomere is perpendicular to the surface of the embryo, each daughter cell becomes trophoblast. B, If the plane of cleavage is parallel to the surface, the daughter blastomere located at the surface becomes trophoblast, whereas the daughter cell located on the interior becomes part of the inner cell mass. Even though by the 16-cell stage the”
― Bruce M. Carlson, Human Embryology and Developmental Biology [with Student Consult Online Access]

“Experimental evidence suggests that a key element underlying a daughter cell's becoming an outer cell is inheritance of a patch of outer cell membrane containing microvilli and the actin microfilament-stabilizing protein, ezrin. The proteins that produce polarity in the outer cells are postulated to direct their differentiation toward the trophoblastic lineage. Common to the inside-outside hypothesis and the cell polarity model is the recognition that a cell that does not contact the surface does not differentiate into trophoblast, but rather becomes part of the inner cell mass.”
― Bruce M. Carlson, Human Embryology and Developmental Biology [with Student Consult Online Access]