Chemokine signaling controls endodermal migration during zebrafish gastrulation.

Directed cell movements during gastrulation establish the germ layers of the vertebrate embryo and coordinate their contributions to different tissues and organs. Anterior migration of the mesoderm and endoderm has largely been interpreted to result from epiboly and convergent-extension movements that drive body elongation. We show that the chemokine Cxcl12b and its receptor Cxcr4a restrict anterior migration of the endoderm during zebrafish gastrulation, thereby coordinating its movements with those of the mesoderm. Depletion of either gene product causes disruption of integrin-dependent cell adhesion, resulting in separation of the endoderm from the mesoderm; the endoderm then migrates farther anteriorly than it normally would, resulting in bilateral duplication of endodermal organs. This process may have relevance to human gastrointestinal bifurcations and other organ defects.