The role of gap junctions in patterning of the chick limb bud

Abstract

The role of gap junctional communication during patterning of the chick limb has been investigated. Affinity-purified antibodies raised against rat liver gap junctional proteins were used to block communication between limb mesenchyme cells. Co-injection of the antibodies and Lucifer yellow into mesenchyme cultures demonstrated that communication was inhibited almost immediately. When antibodies were loaded into mesenchyme tissue by DMSO permeabilization, [3H]nucleotide transfer was prevented for at least 16 h. Polarizing region tissue from the posterior limb bud margin causes digit duplications when grafted to the anterior margin. Quail polarizing region cells were loaded with gap junction antibody and grafted into chick wing buds. The antibody had no effect on growth or survival of the grafted cells. As very few polarizing region cells are required to initiate duplications, the number of polarizing region cells in the grafts was reduced by diluting 1:9 with anterior mesenchyme tissue. When either polarizing region or anterior mesenchyme tissue in the graft was loaded separately with antibody, there was little effect on respecification of the digit pattern. However, loading both tissues in the graft caused a significant decrease in duplications. This indicates that a major role of gap junctions in limb patterning may be to enable polarizing region cells to communicate directly with adjacent anterior mesenchyme. A role for gap junctional communication between anterior mesenchyme cells cannot be excluded. The results are discussed in relation to the role of retinoic acid as a putative morphogen.

Cellular Mechanisms of Pattern Formation in the Developing Limb

“…It appears that the signalis not transmitted across the entire AP axis ofthe limb, and that cooperation between the polarizingcells and an intact apical ectodermal ridge (AER) is important for positional signaling (Tickle et aL., 1975). Furthermore, functional gap junctions are required for polarizing region cells to communicate with anterior mesenchyme, since blocking antibodies to rat liver gap junctional proteins block polarizing zone induced limb duplications (AlIen et aL., 1990). It appears that only cells in the progress zone are capable of responding to the duplicating property of the ZPA (Summerbell, 1974a).These may be the same cells that express Hox7.1 (Hill et aL., 1989;Robert et aL., 1989).…”

“…It is apparent that although the models discussed above would satisfy several of the entries in such a list, they are too simple to satisfy all ofthem (see, e.g., Martin and Lewis, 1986;Wolpert, 1989;Wolpert and Hornbruch, 1990).Recent experimental observations suggest a hierarchy of control mechanisms wherein parameters in the above models, which have largely been assumed constant in the theory, vary in space and time and may themselves be the solutions of other models operating at a different level in the hierarchy. For example, the diffusion coefficientsin the RD systems may vary due to the spatial and temporal differences in gapjunction permeability (AlIen et al, 1990)which may, in turn, be controlled by some other mechanism.…”

Cellular responses in the FGF10‐mediated improvement of hindlimb regenerative capacity in Xenopus laevis revealed by single‐cell transcriptomics

“…We compared gene expression profiles of both samples at the whole transcriptome level, and detected gap junction protein alpha 1.L ( gja1.L ) as a downregulated gene in the FGF10‐treated sample (Table S3). gja1 encodes connexin 43, a component of a gap junction channel (Söhl & Willecke, 2004) that is required for the appropriate expression of morphogens and thus limb bud patterning (Allen et al, 1990; Makarenkova & Patel, 1999; Söhl & Willecke, 2004). Downregulation of gja1.L in the FGF10‐treated sample might suggest that precise control of its expression is required for limb morphogenesis.…”