Developmental system drift in dorsoventral patterning is linked to transitions to autonomous development in Annelida (opens in new tab)

The Bone Morphogenetic Protein (BMP) pathway is the ancestral signalling system patterning the dorsoventral axis in bilaterally symmetrical animals. However, in Spiralia, a large bilaterian clade including molluscs and annelids, BMP’s axial function varies across species, obscuring the ancestral developmental role of this pathway. Here, we study four annelid species to demonstrate that BMP is ancestrally downstream of ERK1/2 and promotes dorsoventral development in Annelida. Importantly, this...