Cellular and molecular characteristics of blastoderm adhesion of the chick embryo.

OBJECTIVE: During early avian development, the blastoderm border must adhere to the vitelline membrane (VM) in order to spread tissue evenly. Classical studies have demonstrated that blastoderm edge tissue possesses intrinsic adhesive properties to the VM; however, the spatial extent, developmental changes, and molecular characteristics of this adherence remain poorly understood. This study aimed to characterize the molecular and functional properties of blastoderm adhesion to the VM.

METHODS: Explant assays were performed using chick embryos at different developmental stages. Tissues were isolated from defined blastoderm regions and cultured on the VM to assess intrinsic regional adhesive properties. Edge-associated gene expression and cytoskeletal organization were analyzed by in situ hybridization and immunohistochemistry.

RESULTS: Explants derived from blastoderm edge regions adhered to the VM at all the newly generated cut edges. However, the adhesive properties became restricted distally during development, with later-stage explants showing loss of attachment at the proximal regions, indicating that adhesive properties are intrinsic to edge regions of blastoderms and become confined distally during development. In explants, the adhesive area extended beyond the narrow distal edge observed in intact embryos. Moreover, the molecular features of edge cells in intact embryos (e.g., edge-associated gene expression and cytoskeletal enrichment) displayed a regionally biased distribution within the expanded edge of the explants.

CONCLUSION: Blastoderm adhesion to the VM is governed by intrinsic tissue properties that are developmentally regulated and locally specific. Physical attachment to the VM and molecular edge identity are spatially uncoupled, suggesting that epithelial adhesion during early morphogenesis is regulated through coordinated but partially independent molecular and mechanical processes.