Genetic analysis of metamorphic and premetamorphic Xenopus ciliary marginal zone

A major event affecting the eye during amphibian metamorphosis is an asymmetrical growth of the ventrotemporal portion of the retina compared with its dorsonasal counterpart. This event is due to an increased proliferation of the precursors of the ventral ciliary marginal zone (CMZ). Here, we analyze the expression patterns of several key homeobox genes implicated in eye development (Xrx1, Xvax2, Xsix3, Xpax6, Xchx10, Xotx2) to understand whether they are active at the time in which the metamorphic changes of the retina occur. We also analyze their expression patterns in the ventral and dorsal CMZ and compare them with bromodeoxyuridine incorporation in the CMZ. Our results suggest that the metamorphic CMZ maintains the functional subdivisions described during embryonic development. Moreover, we find that genes involved in proliferation and cell type determination of the embryonic retina are actively transcribed in the proliferating CMZ, thus indicating a potential regulatory role for these genes in the metamorphic retina.