Correlation between tectum formation and expression of two PAX family genes, PAX7 and PAX6, in avian brains.

Heterotopic transplantation of brain vesicles between chick and quail were performed, and the correlation between tectum formation and the expression of two PAX family genes, PAX7 and PAX6, analyzed. Reciprocal transplantation between the prosencephalon and mesencephalon showed that formation of the tectum always coincided with induction/maintenance of PAX7 and suppression of PAX6, indicating that switch-on or -off of these two PAX family genes in region specific manners are responsible for the differentiation of brain vesicles into the tectum. On the other hand, transplantation of the mesencephalic floor plate into the dorsal mesencephalon suppressed PAX7 expression in the dorsal mesencephalon and changed its fate from the tectum to the tegmentum, indicating that factors in the mesencephalic floor plate suppress PAX7 and limit tectum territory to the dorsal part of the mesencephalon.