Chick PTPσ (cPTPσ), also known as CRYPα, is a receptor-like protein tyrosine phosphatase found on axons and growth cones. Putative ligands for cPTPσ are distributed within basement membranes and on glial end feet of the retina, optic nerve, and optic tectum, suggesting that cPTPσ signaling is occurring along the whole retinotectal pathway. We have shown previously that cPTPσ plays a role in supporting the retinal phase of axon outgrowth. Here we have now addressed the role of cPTPσ within retinal axons as they undergo growth and topographic targeting in the optic tectum. With the use of retroviruses, a secretable cPTPσ ectodomain was ectopically expressed in ovo in the developing chick optic tectum, with the aim of directly disrupting the function of endogenous cPTPσ. In ovo, the secreted ectodomains accumulated at tectal sites in which cPTPσ ligands are also specifically found, suggesting that they are binding to these endogenous ligands. Anterograde labeling of retinal axons entering these optic tecta revealed abnormal axonal phenotypes. These included the premature stalling and arborization of fibers, excessive pretectal arbor formation, and diffuse termination zones. Most of the defects were rostral of the predicted termination zone, indicating that cPTPσ function is necessary for sustaining the growth of retinal axons over the optic tectum and for directing axons to their correct sites of termination. This demonstrates that regulation of cPTPσ signaling in retinal axons is required for their topographic mapping, the first evidence of this function for a receptor-like protein tyrosine phosphatase in the retinotectal projection.

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Keywords Axon guidance, Dil, Optic tectum, Retina, Topographic, Tyrosine phosphatase, PTPσ
Journal Journal of Neuroscience
Rashid-Doubell, F. (Fiza), McKinnell, I.W, Aricescu, A.R. (A. Radu), Sajnani, G. (Gustavo), & Stoker, A. (Andrew). (2002). Chick PTPσ Regulates the Targeting of Retinal Axons within the Optic Tectum. Journal of Neuroscience, 22(12), 5024–5033.