Regulatory interrelations among topographic molecules CBF1, CBF2 and EphA3 in the developing chick retina

It has been shown that topographic expression of two winged-helix transcription factors, CBF1/c-qin and CBF2, and a receptor tyrosine kinase EphA3 (Mek4/Cek4) play important roles in establishing the topographic retinotectal projection map along the rostrocaudal axis. The interrelationship among these topographic molecules in the chick retina was studied during development. The topographic expression of CBF1 and CBF2 preluded the graded expression of EphA3, but their precise expression profiles did not exactly fit together. However, interestingly, CBF1 and CBF2 were properly expressed, together with EphA3, in immortalized cell lines derived from the quail retina, which maintained position-specific characteristics. The expression of another topographic molecule SOHo-1, the sensory organ homeobox-1 transcription factor, was separate from EphA3 expression. Ectopic expression of CBF1 using in ovo electroporation repressed the expression of CBF2, and misexpression of CBF2 influenced the graded localization of EphA3 in the retina, albeit imperfectly. Taken together, it is suggested that retinal cells first begin to express CBF1 or CBF2 according to their topographic positions, generate cellular descendants in which the expression of CBF1 and CBF2 is maintained cell-autonomously, and then establish the nasotemporal gradient of EphA3 under the control of CBF2, although indirect.