Expression profiles suggest a role for Pax7 in the establishment of tectal polarity and map refinement.

The role for Pax7 in establishing tectal polarity and map refinement was authenticated by gene expression studies in vivo and in vitro. Throughout development (stages E2-E12 were examined) a rostral(low)-caudal(high) and dorsal(high)-ventral(low) Pax7 expression gradient was detected immunohistochemically in the chick optic tectum, indicating a role for Pax7 in establishing tectal polarity. Chick retino-recipient tectal cells positive for Pax7 also co-expressed ephrin-A2, a molecule involved in the establishment and refinement of the retinotopic map. In vitro, PAX7 up-regulated ephrin-A2 when transfected into undifferentiated P19 cells; cells became negative for both Pax7 and ephrin-A2 protein following treatment with anti-sense oligonucleotides. These results suggest that in addition to being involved in the early establishment of tectal polarity, Pax7 plays a later role in retino-tectal map formation and refinement.