Fig. 8. A model for the roles of Bmp in ventral fate specification beyond the early gastrula stages. Depiction of the posterior body of an 18 hpf wild-type embryo. The kidney terminus (KT) is migrating around the end of the yolk extension to reach the ventral limit of the tail, where it will subsequently remodel and form the presumptive cloaca. Between the mid-gastrula and early somitogenesis stages (4-10 hours prior to the stage illustrated), continuous ventral Bmp signaling is necessary for patterning the tissues shaded in pink, which include the ventral tail fin (VTF), ventral mesoderm (VM; where hrT is expressed) and the proctodeum (Pr). Within the ventral mesoderm, HrT plays a crucial role in suppressing blood fate and activating the transcription of factors that are important for the proper morphogenesis of the cloaca. We hypothesize that a signaling factor secreted from the proctodeal cells guides the migration and remodeling of the kidney terminus to form the cloaca.