The Journal of Neuroscience, June 15, 2002, 22(12):5024-5033
Chick PTP
Regulates the Targeting of Retinal Axons within the
Optic Tectum
Fiza
Rashid-Doubell,
Iain
McKinnell,
A. Radu
Aricescu,
Gustavo
Sajnani, and
Andrew
Stoker
Neural Development Unit, Institute of Child Health, London WC1N
1EH, United Kingdom
Chick PTP
(cPTP
), also known as CRYP
, is a receptor-like
protein tyrosine phosphatase found on axons and growth cones. Putative
ligands for cPTP
are distributed within basement membranes and on
glial end feet of the retina, optic nerve, and optic tectum, suggesting
that cPTP
signaling is occurring along the whole retinotectal pathway. We have shown previously that cPTP
plays a role in
supporting the retinal phase of axon outgrowth. Here we have now
addressed the role of cPTP
within retinal axons as they undergo
growth and topographic targeting in the optic tectum. With the use of retroviruses, a secretable cPTP
ectodomain was ectopically expressed in ovo in the developing chick optic tectum, with the
aim of directly disrupting the function of endogenous cPTP
.
In ovo, the secreted ectodomains accumulated at tectal
sites in which cPTP
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 cPTP
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 cPTP
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.
Key words:
tyrosine phosphatase, PTP
; axon guidance; topographic; retina; optic tectum; DiI
Copyright © 2002 Society for Neuroscience 0270-6474/02/22125024-10$05.00/0