Fig. 7. TBX-37, TBX-38 expression and the first and second Notch interactions. Schematic diagrams of ABa and ABp development in wild-type embryos, apx-1 embryos, and apx-1; tbx-37 tbx-38 mutant embryos. (A) Arrows extending from MS indicate ABa and ABp descendants that contact MS or its sister, E (not shown). (B) When ABa or ABp descendents express TBX-37, TBX-38 and are signaled by MS or E, they adopt the tertiary fates shown and become mesodermal precursors. (C) The ABp descendants are assumed here to adopt secondary fates in the apx-1; tbx-37 tbx-38 mutant embryos because these embryos form tails. Fates of ABa descendants presumably are the same as in tbx-37 tbx-38 mutant embryos, but were not examined directly (indicated by?).