Notch signaling can inhibit Xath5 function in the neural plate and developing retina

Neuronal differentiation Is regulated by both positive and negative regulat ory factors; however, precisely how these factors interact to regulate reti nogenesis Is still unclear. We have examined the ability of the Notch pathw ay to modulate the function of the basic helix-loop-helix factor Xath5. Ove rexpression of Xath5 by RNA injection into cleavage-stage blastomeres promo tes ectopic neurogenesis at neural plate stages and ganglion cell different iation in the developing retina. We found that these activities of Xath5 co uld be inhibited by coexpression of activated Notch. Notch inhibition of Xa th5 function was reversed by coexpression with the zinc finger protein X-My T1. The Notch effector enhancer-of-split related 1 (ESR1) also blocked Xath 5 activity but efficient inhibition by ESR1 required the DNA binding basic domain and the conserved WRPW motif. In addition, ESR1 inhibited the abilit y of Xath5 to directly activate the expression of XBrn3d, a transcription f actor involved in retinal ganglion cell development. Xath5 could upregulate expression of X-Delta-1, ESR1, and ESR3, suggesting that Xath5 participate s in a regulatory loop with the Notch pathway.