Neuronal locus specificity: altered pattern of spatial deployment in fused fragments of embryonic xenopus eyes.

Before optic nerve outgrowth in Xenopus laevis embryos, a change of state occurs in the differentiating retinal cell population which renders the cells refractory to information about subsequent changes in their positions, and commits individual ganglion cells to develop specific position-dependent properties (locus specificities) which subserve the formation of orderly retinotopic connections in the optic tectum. When different parts of eye primordia from stages before optic nerve outgrowth are fused, each piece in such a reconstructed eye does not generate ganglion cells with the partial-set of locus specificities normally arising from that region of the intact eye. It is inferred that separate parts of the early embryonic retina do not contain stable programs for spatial deployment of locus specificity, and that development of definitive locus specificities in retinal ganglion cells requires additional cellular interactions among the retinal cells later in development.