Nodal and Churchill regulate the expression of a Notch ligand during the segregation of germ layers in Xenopus.

LÓPEZ, SILVIA L.; FAVAROLO, MARÍA BELÉN; SABAJ, DANIELA

Buenos Aires

Congreso; Xth Latin American Society for Developmental Biology (LASDB) Meeting.; 2019

Latin American Society for Developmental Biology (LASDB)

We previously showed that Notch1 participates in the segregation of the three germ layers in Xenopus by refining the boundary between the endomesoderm and the ectoderm and between the mesoderm and the endoderm. The Dll1 ligand is expressed during gastrulation in the pre-involuted mesoderm and is involved in the former step (Revinski et al., 2010).We wondered if Nodal (a key player in endomesoderm induction) modulates Notch signaling. We demonstrate that secreted Nodal from the vegetal cells activates its effector smad2 in the endomesoderm, promoting endoderm specification and repressing dll1 and mesoderm specification in a cell-autonomous way. In turn, these endodermal cells secrete Nodal, which induces mesoderm and the expression of dll1 in a non-cell autonomous way. This sequential activation of Nodal signaling contributes to endomesoderm segregation into endoderm and mesoderm and ensures that dll1 is expressed in the presumptive mesoderm.The transcription factor Churchill (ChCh) favors neuroectodermal vs. mesodermal fates in birds. We detected Xenopus ChCh transcripts in the dorsal animal region from midblastula stage and in neuroectoderm in neurulas. Therefore, we wondered if ChCh modulates Notch signaling during germ layers segregation. Blocking ChCh function expanded the dll1 domain, while a ChCh transactivating construct inhibited dll1 expression. We conclude that ChCh negatively regulates dll1.