Role of Notch signalling in Xenopus blastula

ACOSTA, HELENA; LÓPEZ, SILVIA LILIANA; PAGANELLI, ALEJANDRA R.; CARRASCO, ANDRÉS E.

Buenos Aires

Congreso; 4th International Meeting of the Latin American Society of Developmental Biology; 2008

Latin American Society for Developmental Biology

Two signalling centers coexist in the Xenopus blastula: 1) the dorsal-animal region constitutes the BCNE center, which expresses chordin, noggin, nodal-3 and siamois, and contains the precursor cells of the Spemann-Mangold organiser and its derivatives (the floor plate and the notochord) and the prospective brain; 2) the Nieuwkoop center, more vegetally located, which expresses nodal-2, nodal-6 and Cerberus, and later forms the head endoderm (Kuroda et al., 2004; Plos Biol 2, 623-633). We have previously shown that Notch signalling is involved in the development of the organiser derivatives in Xenopus laevis (López et al., 2003; Development 130: 2225-2238). However, it is not clear whether this pathway has a role during earlier stages of development, before gastrulation. We began to study whether Notch signalling participates in the development of the blastula centers. We found that constitutively active NotchICD strongly decreases the expression of the BCNE markers chordin, foxA4 and Xnr3. This suggests that Notch may be an inhibitor of BCNE specification. To confirm this, we performed experiments where Notch signalling was blocked either by injection of Su(H)DBM mRNA (which interferes with the canonical CSL-dependent pathway) or by knock-down with an antisense morpholino against Notch (Notch Mo). Both strategies resulted in an increase of the expression of chordin, foxA4 and Xnr3. However, while blocking the CSL pathway gives more variable results (i.e. decrease of foxA4a in some embryos), the results with the Notch Mo were more consistent. Moreover, we also observed an expansion of the three markers analysed towards the vegetal region of the blastula, which normally contains the Nieuwkoop center. These results suggest that Notch signalling may be refining the limits between both centers and that non-canonical mechanisms may be contributing.