THE PATTERN OF PROTEIN AND GLYCOPROTEIN-SYNTHESIS IN PRESUMPTIVE LENS AND NONLENS ECTODERM OF THE CHICKEN-EMBRYO

Lens induction is a classic example of the tissue interactions that lead to cell specialization during early vertebrate development. Previous studies have shown that a large region of head ectoderm, but not trunk ectoderm, of 36 h (stage 10) chicken embryos retains the potential to form lenses and synthesize the protein delta-crystallin under some conditions. We have used polyacrylamide gel electrophoresis and fluorography to examine protein and glycoprotein synthesis in presumptive lens ectoderm and presumptive dorsal (trunk) epidermis to look for differentiation markers for these two regions prior to the appearance of delta-crystallin at 50 h. Although nearly all of the proteins incorporating H-3-leucine were shared by presumptive lens ectoderm and trunk ectoderm, these two regions showed more dramatic differences in the incorporation H-3-sugars into glycoproteins. When non-lens head ectoderm that has a capacity for lens formation in vitro was labeled, a hybrid pattern of glycoprotein synthesis was discovered: glycoproteins found in either presumptive lens ectoderm or trunk ectoderm were oftentimes also found in other head ectoderm. Therefore, molecular markers have been identified for three regions of ectoderm committed to different fates (lens and skin), well before features of terminal differentiation begin to appear in the lens.