Sequential signaling crosstalk regulates endomesoderm segregation in sea urchin embryos

Segregation of endoderm and mesoderm lineages is a fundamental event in early embryogenesis. Using sea urchin embryos, Sethi et al. (p. [590][1]) found that Notch and canonical Wnt pathways crosstalk progressively partitions the endomesoderm to discrete endoderm and mesoderm fates. This three-step signaling exchange demonstrates how the timing of signaling crosstalk is regulated in vivo through temporally and spatially staggered genetic circuits that intersect only at specific developmental stages. [1]: /lookup/doi/10.1126/science.1212867