NF-protocadherin and TAF1 regulate retinal axon initiation and elongation in vivo.

NF-protocadherin (NFPC)-mediated cell-cell adhesion plays a critical role in vertebrate neural tube formation. NFPC is also expressed during the period of axon tract formation, but little is known about its function in axonogenesis. Here we have tested the role of NFPC and its cytosolic cofactor template-activating factor 1 (TAF1) in the emergence of the Xenopus retinotectal projection. NFPC is expressed in the developing retina and optic pathway and is abundant in growing retinal axons. Inhibition of NFPC function in developing retinal ganglion cells (RGCs) severely reduces axon initiation and elongation and suppresses dendrite genesis. Furthermore, an identical phenotype occurs when TAF1 function is blocked. These data provide evidence that NFPC regulates axon initiation and elongation and indicate a conserved role for TAF1, a transcriptional regulator, as a downstream cytosolic effector of NFPC in RGCs.