ACTIVIN CAN INDUCE THE FORMATION OF AXIAL STRUCTURES AND IS EXPRESSED IN THE HYPOBLAST OF THE CHICK

We show that PIF/activin can induce the formation of axial structures including a full-length notochord, segmented somites, and a neural tube in isolated epiblasts from chick blastulae. Using degenerate PCR primers, we have cloned a fragment of the activin βB chain from chick hypobiast cDNA, and a fragment of the activin βA chain from chick genomic DNA. Furthermore, we show that in the chick, activin is transcribed precisely when axial mesoderm is being induced. Since exogenous PIF/activin can induce the formation of axial structures and since activin βB is transcribed at the time and place where the mesodermal axial structures are being induced, we propose that in the chick, activin B is the endogenous inducer of the body axis. © 1990.