By default, the information is derived from experiments at the mRNA level, unless specified ???at the protein level???.</p><p><a href='../manual/tissue_specificity' target='_top'>More...</a></p>Tissue specificityiExpressed in a gradient at the caudal end of the embryo during gastrulation and later in the distal-most aspect of several structures that extend from the body such as the limbs and genit