The LIM-homeodomain gene family in the developing Xenopus brain: Conservation and divergences with the mouse related to the evolution of the forebrain

A comparative analysis of LIM-homeodomain (LIM-hd) expression patterns in t he developing stage 32 Xenopus brain is presented. x-Lhx2, x-Lhx7, and x-Lh x9 were isolated and their expression, together with that of x-Lhx1 and x-L hx5, was analyzed in terms of prosomeric brain development and LIM-hd combi natorial code and compared with mouse expression data. The results show an almost complete conservation of expression patterns in the diencephalon. Th e Lhx1/5 and Lhx2/9 subgroups label the pretectum/ventral thalamus/zona lim itans versus the dorsal thalamus, respectively, in alternating stripes of e xpression in both species. Conversely, strong divergences in expression pat terns are observed between the telencephalon of the two species for Lhx1/5 and Lhx2/9. Lhx7 exhibits particularly conservative patterns and is propose d as a medial ganglionic eminence marker. The conservation of diencephalic segments is proposed to mirror the conservative nature of diencephalic stru ctures across vertebrates. In contrast, the telencephalic divergences are p roposed to reflect the emergence of significant novelty in the telencephalo n (connectivity changes) at the anamniote/amniote transition. Moreover, the data allow the new delineation of pallial and subpallial domains in the de veloping frog telencephalon, which are compared with mouse subdivisions. In the pallium, the mouse combinatorial expression of LIM-hd is notably riche r than in the frog, again possibly reflecting evolutionary changes in corti cal connectivity.