Journal of Neuroscience, Vol 7, 3764-3782, Copyright © 1987 by Society for Neuroscience
Healing and growth of half-eye "compound eyes" in Xenopus: application of an interspecific cell marker
S O'Gorman, J Kilty and RK Hunt
Salk Institute for Biological Studies, La Jolla, California 92037.
Surgically constructed compound eyes have been widely used to examine the
development of retinotectal projections in amphibians. Such studies have
been limited, however, by the lack of an adequate cellular marker with
which to assess the contributions of grafted and host tissues to the later
larval and adult retina. We have followed the growth of graft- and
host-derived ocular tissues in interspecific compound eyes prepared by
orthotopic and heterotopic exchanges of half-eye fragments between
pigmented Xenopus borealis and albino Xenopus laevis embryos. This
genotypic combination allowed the growth of graft-derived choroid and
pigment epithelium to be studied in the living animal, and permitted
cell-by-cell resolution of graft- and host-derived neurons in
quinacrine-stained paraffin sections. At mid- and late-larval stages
graft-derived neurons occupied large and usually coherent territories of
retina in all classes of orthotopic and heterotopic compound eyes. In
successfully healed cases, sample means of the percentage of the total
retina occupied by graft-derived neurons ranged from 43 to 51%.
Graft-derived territories originated near the optic nerve head and extended
into the germinal neuroepithelium at the retinal periphery. As compared to
orthotopic compound eyes, graft-derived territories in all classes of
heterotopic compound eyes were slightly smaller and significantly more
variable. Despite this variability, the correlation between graft-derived
pigment epithelial and retinal territories was quite good in heterotopic
compound eyes. While graft-host borders were generally sharp, there was
also evidence of local cell mixing over distances of several cell diameters
in the inner nuclear and ganglion cell layers. Single displaced cells,
isolated from other members of their genetic cohort by 5 or more cell
diameters, were also present in the inner nuclear and ganglion cell layers.