The study of pattern formation and regeneration in embryonic and larval Xenopus laevis retinal tissue.

摘要

In embryonic form, the retina of the frog Xenopus laevis has provided a reliable system for the study of regeneration and visuotectal pattern formation. Regeneration involves the restoration and/or replacement of appropriate missing tissues. Pattern formation involves the acquisition and interpretation of a cell's positional information. During both normal development and regeneration, newly created cells are assigned positional values and then interpret this information as a result of pattern formation (Wolpert, 1978). It has been hypothesized that retinal ganglion cells learn unique positional addresses in the eye primordium's positional field and, that ganglion cells use these addresses to form correct connections with visual brain cells (visuotectal pattern formation; Sperry, 1951).;Previous studies have shown that the embryonic Xenopus retina readily regenerates after partial extirpation of the developing eye bud (Feldman and Gaze, 1975; Berman and Hunt, 1975; Hunt and Berman, 1975; Ide et al. 1979; Ling et al. 1979; Straznicky et al. 1980; Ide et al. 1987). It has also been shown that during the regeneration of nasal one-third sized fragments made at embryonic stage 32, retinal ganglion cells form twinned or mirror image duplicated projections to the midbrain optic tectum (Ide et al. 1984, 1987). In the regenerating Xenopus retinal system, the duplication of visuotectal pattern implies that some modification has been made in the original patterning of these tissues. In this situation, two distinct retinal areas contain identical positional information for connectivity with the same visual brain location.;This study explores the morphological expression of healing and growth which underlies successful regeneration and, relates these data to pattern formation observed during regeneration. In the embryonic and larval retinal regenerating systems, cell movements and extra cell division directly correlate with pattern duplication seen during regeneration. Similarities in cell behavior during regeneration suggest that similar mechanisms are controlling these two events. By studying cellular aspects of pattern formation during regeneration, we can better understand the rules by which cell fate is determined. These data provide a starting point for further studies concerning molecular mechanisms which underlie regenerative pattern formation.