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Abstract:
Background: Bone morphogenetic proteins (Bmps) are
required for the specification of ventrolateral cell fates
during embryonic dorsoventral patterning and for
proper convergence and extension gastrulation movements,
but the mechanisms underlying the latter role
remained elusive.
Results: Via bead implantations, we show that the Bmp
gradient determines the direction of lateral mesodermal
cell migration during dorsal convergence in the zebrafish
gastrula. This effect is independent of its role during
dorsoventral patterning and of noncanonical Wnt signaling.
However, it requires Bmp signal transduction
through Alk8 and Smad5 to negatively regulate Ca2+/
Cadherin-dependent cell-cell adhesiveness. In vivo,
converging mesodermal cells form lamellipodia that attach
to adjacent cells. Bmp signaling diminishes the
Cadherin-dependent stability of such contact points,
thereby abrogating subsequent cell displacement
during lamellipodial retraction.
Conclusions: We propose that the ventral-to-dorsal
Bmp gradient has an instructive role to establish a
reverse gradient of cell-cell adhesiveness, thereby
defining different migratory zones and directing lamellipodia-
driven cell migrations during dorsal convergence
in lateral regions of the zebrafish gastrula.
