Isolated large micromeres from a 16-cell embryo can independently form:
Classical isolation experiments by Sven Hörstadius cultured separated micromeres from 16-cell sea urchin embryos in isolation. Even without ectodermal cues, large micromeres undergo epithelial-mesenchymal transition, migrate within culture droplet and secrete calcium carbonate forming characteristic triradiate spicules typical of larval skeleton. They autonomously express Alx1, Sm50, Msp130 and other biomineralization genes under Pmar1-HesC circuit control. This proves skeletogenic program intrinsic to micromeres, not requiring inductive interactions. Other lineages lose ability to form gut or
Ref: Hörstadius, Experimental Embryology of Echinoderms, 1973; Gilbert 12th ed., Chapter 8: Micromere autonomy tests.
