Notch3is a genetic modifier of NODAL signalling for patterning asymmetry during mouse heart looping

The TGFβ secreted factor NODAL is a major left determinant required for the asymmetric morphogenesis of visceral organs, including the heart. Yet, when this signalling is absent, shape asymmetry, for example of the embryonic heart loop, is not fully abrogated, indicating that there are other factors regulating left-right patterning. Here, we used a tailored transcriptomic approach to screen for genes asymmetrically expressed in the field of heart progenitors. We thus identifyNotch3as a novel left-enriched gene and validate, by quantitative in situ hybridization, its transient asymmetry in the lateral plate mesoderm and node crown, overlapping withNodal. In mutant embryos, we analysed the regulatory hierarchy and demonstrate thatNodalin the lateral plate mesoderm amplifiesNotch3asymmetric expression. The function ofNotch3was uncovered in an allelic series of mutants. In single neonate mutants, we observe thatNotch3is required with partial penetrance for the development of ventricles, in addition to its known role in coronary arteries. In compound mutants, we reveal thatNotch3acts as a genetic modifier ofNodal, able to modulate heart looping direction and the curvature of the outflow tract. WhereasNotch3was previously associated with the CADASIL syndrome, its contribution to asymmetric organogenesis is now relevant to severe laterality defects such as the heterotaxy syndrome.