Wnt dynamics at the blastopore and stomodeum during sea urchin gastrulation

In the sea urchin embryo, as many as ten Wnts are expressed by cells that undergo gastrulation movements. Here, Wnt1, 5, 6, 7, 8 and 16 are examined to learn details of expression and function over time using results from a temporal scRNA-seq analysis coupled with hybridization chain reaction in situ analysis in which multiple wnt genes are localized simultaneously in the same embryo. The data reveal that many cells express two or three wnt genes at the same time. A single sharp boundary of expression is seen just lateral to the blastopore. Other boundaries of expression are graded and change over developmental time. Functionally, experiments show that Wnts control expression and/or patterning of other wnt genes, and they control expression of marker genes during and following invagination of the archenteron. Stomodeum formation also requires Wnt signaling, indicating that the entire gut uses Wnt signaling for diversification of endodermal fates.