Non-migratory mode of ventral body wall closure: Primary mid-ventral covering is replaced by prospective definitive body wall.

BACKGROUND: During ventral body wall closure in amniotes, the skeleton and muscles such as sternum, ribs, and pectoral muscles undergo a striking positional change from the dorso-lateral to mid-ventral region. The precise process of ventral body wall closure has poorly been explored. We have presented and examined two opposing models: the invading closure model, in which musculoskeletal components infiltrate into the mid-ventral tissue, and the replacing closure model, in which the original mid-ventral tissue degenerates to be replaced by the dorso-lateral body wall.

RESULTS: We developed a new method that enables direct cell labeling with PKH dyes in late chicken embryos. Our PKH labeling has shown that the original mid-ventral tissue, including both mesodermal and ectodermal cells, is progressively confined to the midline as the closure proceeds, contradicting the invading closure model. Moreover, the dorso-lateral tissue, including not only musculoskeletal but also non-musculoskeletal components, eventually contributes to the mid-ventral region. These results support the replacing closure model.

CONCLUSION: The ventral body wall closure is achieved in a replacing manner. The mid-ventral region of the early body wall is a transient structure to cover the ventral surface, which is eventually eliminated to be replaced by the dorso-lateral region that represents the future definitive body wall.