Embryonic pattern formation without morphogens.

One of the earliest and most-fundamental pattern- formation events in embryonic development is endoderm and mesoderm specification. In sea urchin embryos, this process begins with blimp1 and wnt8 gene expression at the vegetal pole as soon as embryonic transcription begins. Shortly afterwards, wnt8/blimp1 expression spreads to the adjacent ring of mesoderm progenitor cells and is extinguished in the vegetal-most cells. A little later, the ring of wnt8/blimp1 activity moves out of the mesoderm progenitors and into the neighboring endoderm cells. Remarkably, this moving ring of gene expression has now been shown to be controlled entirely by transcriptional cis-regulatory logic.1.