Pitx2c orchestrates embryonic axis extension via mesendodermal cell migration.

Pitx2c, a homeodomain transcription factor, is classically known for its left-right patterning role. However, an early wave of expression occurs at the onset of gastrulation in several species, indicating a possible earlier role that remains relatively unexplored. Here we show that in zebrafish, maternal-zygotic (MZ) mutants exhibit a shortened body axis indicative of convergence and extension (CE) defects. Live imaging reveals that MZ mutants display less persistent mesendodermal migration during late stages of gastrulation. Transplant data indicate that Pitx2c functions cell non-autonomously to regulate this cell behavior by modulating cell shape and protrusive activity. Using transcriptomic analyses and candidate gene approaches, we identify transcriptional changes in components of the chemokine-ECM-integrin dependent mesendodermal migration network. Together, our results define pathways downstream of Pitx2c that are required during early embryogenesis and reveal novel functions for Pitx2c as a regulator of morphogenesis.