13-P117 Dazap2, a novel cdx-independent posteriorizing factor, is required for FGF activity in neural patterning

In the embryonic telencephalon, Pax6 is expressed in the progenitors of the pallium in a caudal to rostral gradient and governs the anteroposterior and dorsoventral patterning of the telencephalon. The pallial–subpallial boundary (PSPB) is both a physical and gene expression boundary separating dorsal and ventral telencephalon. Previous studies have indicated that Pax6 is required for establishment and maintenance of this boundary. However, it is largely unknown how Pax6 exerts its effects at the molecular level at the PSPB. We have performed microarray analysis on tissue from the lateral telencephalon, including the PSPB, to compare gene expression at the onset of neurogenesis (E12) in Pax6 DTy54 and Pax6 DTy54 embryos. The novel DTy54 Pax6 reporter mouse in which cells capable of expressing Pax6 are tauGFP positive allows the PSPB to be visualized by the high expression of tauGFP. The GFP positive cells which express Pax6 were isolated by fluorescence activated cell sorting (FACS) and dissociated to carry out the microarray comparison of gene expression. This analysis identified many novel downstream targets of Pax6 as well as some novel biological processes with which Pax6 has not formerly been associated. Cell cycle processes are prominent themes in the up-regulated gene set of the microarray data. This is consistent with the important role of Pax6 in regulating cell cycle progression in the cortical ventricular zone. To address this issue, we are testing the changes in cell cycle and cell proliferation at the PSPB in Pax6 DTy54 and Pax6 DTy54 embryos using bromodeoxyuridine (BrdU) and iododeoxyuridine (IddU) double labeling.