Notch1 controls dorso-ventral polarity by a dual mechanism during the establishment of the body axes.

ENCINAS, PAULA I; LÓPEZ, SILVIA L.; DIEGO R. REVINSKI; RODRÍGUEZ ABINAL, MATEO; CASTRO COLABIANCHI, AITANA MANUELA; MONTI, RENATO JOSÉ

Medellin

Congreso; IX LASDB Meeting; 2017

Latin American Society for Developmental Biology

Notch1 controls dorso-ventral polarity by a dual mechanism during the establishment of the body axesAitana M. Castro Colabianchi (*), Diego R. Revinski, Paula I. Encinas, Renato J. Monti, Mateo Rodríguez Abinal, Silvia L. López (**)(*) Presenting autor. (**) Corresponding author.An antagonistic interplay between two signalling centers patterns the dorsoventral and anteroposterior body axes in vertebrates. The ventral center, described at gastrula stage, secretes BMP4 and Wnt8. These morphogens induce ventral-posterior fates in the embryo. The dorsal center (the gastrula Spemann-Mangold?s organizer) secretes antagonists and expresses transcriptional repressors of the ventral morphogens, thus protecting the dorsal region from being ventralized and posteriorized. Before gastrulation, dorsal accumulation of maternal nuclear ß-catenin induces the ?blastula chordin- and noggin- expressing center? (BCNE), which contains the precursors of the brain and gives rise to the Spemann-Mangold?s organizer. The BCNE secretes BMP antagonists and expresses transcriptional repressors, initiating a double inhibition of BMP signalling at blastula stages, critical for brain formation. While it is well accepted that β-catenin triggers the transcriptional cascade that establishes the dorsal center, nothing is known about the early events that lead to the establishment of the ventral center.We previously showed that gain of function of Notch1 produces a strong ventralized phenotype in Xenopus. Through functional experiments, we proposed that an early ventral Notch activity restricts the BCNE center to the dorsal side of the blastula by destabilising β-catenin. Now, we are investigating how Notch activity is spatially regulated and whether it can control the development of the ventral center.By immunofluorescence, we found that Notch1 protein is distributed in a ventral to dorsal gradient from the beginning of the embryogenesis in both Xenopus and zebrafish embryos, in a complementary fashion relative to β-catenin, confirming our hypothesis. Lithium chloride decreased the levels of Notch1 protein, indicating that phosphorylation by GSK3 stabilizes Notch1 in early embryos. Gain and loss of function experiments showed that Notch1 controls the expression of ventral center markers. We conclude that ventral accumulation of Notch1 protein is the earliest sign of ventral development, preceding the appearance of the strong localized expression of Wnt8 and BMP4 in the ventral center. Thus, Notch1 is the first and earliest signaling player reported until now to be involved in establishing this center. Together with our previous findings, our results indicate that during early embryogenesis, ventrally located Notch1 controls dorsoventral polarity by a dual mechanism: 1) By promoting the development of the ventral center; 2) By destabilizing the dorsal determinant β-catenin.Key-words: Notch, ventral center, dorsal center, β-cateninUniversidad de Buenos Aires, CONICET, IBCN, Facultad de Medicina, Buenos Aires, Argentina