derriere: a TGF-beta family member required for posterior development in Xenopus

TGF-beta signaling plays a key role in induction of the Xenopus mesoderm an d endoderm, Using a yeast-based selection scheme, we isolated derriere, a n ovel TGF-beta family member that is closely related to Vg1 and that is requ ired for normal mesodermal patterning, particularly in posterior regions of the embryo. Unlike Vg1, derriere is expressed zygotically, with RNA locali zed to the future endoderm and mesoderm by late blastula, and to the poster ior mesoderm by mid-gastrula, The derriere expression pattern appears to be identical to the zygotic expression domain of VegT (Xombi, Brat, Antipodea n), and can be activated by VegT as well as fibroblast growth factor (FGF), In turn, derriere activates expression of itself, VegT and eFGF, suggestin g that a regulatory loop exists between these genes. derriere is a potent m esoderm and endoderm inducer, acting in a dose-dependent fashion, When mise xpressed ventrally, derriere induces a secondary axis lacking a head, an ef fect that is due to dorsalization of the ventral marginal zone. When misexp ressed dorsally, derriere suppresses head formation, derriere can also post eriorize neurectoderm, but appears to do so indirectly. Together, these dat a suggest that derriere expression is compatible only with posterior fates. In order to assess the in vivo function of derriere, we constructed a domi nant interfering Derriere protein (Cm-Derriere), which preferentially block s Derriere activity relative to that of other TGF beta family members. Cm-d erriere expression in embryos leads to posterior truncation, including defe cts in blastopore lip formation, gastrulation and neural tube closure. Norm al expression of anterior and hindbrain markers is observed; however, parax ial mesodermal gene expression is ablated, This phenotype can be rescued by wild-type derriere and by VegT, Our findings indicate that derriere plays a crucial role in mesodermal patterning and development of posterior region s in Xenopus.