06-P004 Co-operative EphA4 reverse and EphB2 forward signaling control proliferation and apoptosis during distal ureter morphogenesis

ing the duplication generates increased levels of EFNB1 transcript, compared to the normal chromosome. We also show that imbalance of ephrin-B1 between X chromosomes in a mouse model containing a hypomorphic Efnb1 conditional allele results in aberrant cell mixing of the cranial primordia during development and hypertelorism. Taken together these data suggest that cellular mosaicism for different levels of ephrin-B1 (as well as simple presence/absence) is an important contributor to craniofacial abnormalities in humans and mice.