Pitx2c regulates 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 pitx2 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) pitx2c mutants exhibit a shortened body axis indicative of convergence and extension (CE) defects. Live imaging reveals that MZpitx2c mutants display less persistent mesendodermal migration during later stages of gastrulation. Transplant experiments 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 Pitx2 that are required during early embryogenesis and reveal novel functions for Pitx2 as a regulator of morphogenesis. MZpitx2c and WT embryos were collected at shield stage to assess the loss of Pitx2c function by microarray. For gain-of-function analysis, embryos were injected at the 1-cell stage with mRNA encoding pitx2c and collected at dome stage for microarray.