Regional differences in cells and embryos can be specified in other ways besides localization of RNAs in the cortex. Two of those ways have been studied in great detail: the “sugar code” and the “bioelectric code.”
Most proteins in living cells — including those in membranes — are chemically bonded to carbohydrates called “glycans” (from the Greek word for “sweet”). The nucleotides in DNA are linked together end-to-end in a linear molecule, so DNA sequence information is one-dimensional. In living cells, the subunits in proteins (with a few exceptions) are also linked in a linear chain. But glycans can be linked together in complex three-dimensional ways, so their information-carrying capacity exceeds that of DNA and proteins by many orders of magnitude.3
The information carried by glycans has been called the “sugar code.”4 The sugar code is “interpreted” by proteins called lectins, which “recognize” specific three-dimensional structures of glycan molecules. Glycans and lectins play an essential role in communication among cells and help to guide cell movements in a developing embryo. Experiments have shown that membrane patterns of glycans change in the course of embryo development.5
In addition to the sugar code, probably all living cells (not just nerve and muscle cells) generate electric fields across their membranes. They do this by pumping charged ions through channels in their membranes, creating a “bioelectric field.” The pattern of membrane channels determines the form of the bioelectric field, and the form of the field changes during embryo development.
Bioelectric fields are correlated with important developmental events. In frog embryos, for example, large ionic currents start flowing out of the sites where the hind limbs will develop long before the limbs actually appear. More.
These, and the many other systems described, cannot have come about simply by natural selection acting on random mutation (Darwinism), no matter what they are teaching in school.
See also: How much does DNA influence cell shape?
2013 paper: Bioelectric code helps govern embryo shape