43. Which of the following is TRUE of a morphogen? It is a signaling molecule that (A) is required for cell-to-cell contact within the embryo. (B) induces the differentiation of cells within the embryo. (C) induces blastulation of the developing embryo. (D) induces implantation of the embryo into the uterus of mammals. (E) that separates out cytoplasmic factors to their respective cells within the developing embryo.