A gradient of gap junctional communication along the anterior-posterior axis of the developing chick limb bud

A modification of the scrape-loading/dye transfer technique was used to study gap junctional communication along the anterior-posterior (A-P) axis of embryonic chick wing buds at an early stage of development (stage 20/21) when positional values along the A-P axis are being specified. Extensive intercellular transfer of the gap junction-permeable dye, lucifer yellow, from scrape-loaded mesenchymal cells to contiguous cells occurs in the posterior mesenchymal tissue of the wing bud adjacent to the zone of polarizing activity, which is thought to be the source of a diffusible morphogen that specifies A-P positional identity according to its local concentration. Considerably less transfer of lucifer yellow dye occurs in scrape-loaded mesenchymal tissue in the middle of the limb bud compared to posterior mesenchymal tissue, and little or no transfer of lucifer yellow is observed in the mesenchymal tissue in the anterior portion of the limb bud. No intercellular transfer of the gap junction-impermeable dye, rhodamine dextran, occurs in any region of the limb bud. These results indicate that there is a gradient of gap junctional communication along the A-P axis of the developing chick wing bud. This gradient of gap junctional communication along the A-P axis might generate a graded distribution of a relatively low molecular weight intracellular regulatory molecule involved in specifying A-P positional identities.