Fig. 8 | Nature Communications

Fig. 8

From: A Hox-TALE regulatory circuit for neural crest patterning is conserved across vertebrates

Fig. 8

Evolutionary model for regulation of Hox2 genes in vertebrates. a A model for evolution of the neural crest (NC) Hox code, based on our data. a NC gene regulatory network (GRN) and NC Hox -code evolved in ancestral vertebrates and are conserved between cyclostomes and gnathostomes. In ancestral vertebrates, Hox2 NC expression was regulated by TALE (Three-Amino-Acid-Loop-Extension) and Hox factors, through a putative ancestral enhancer with shared NC and hindbrain activities. b A model for the divergence of lamprey and mouse Hox2 NC/hindbrain enhancers. Enhancer activity domains are depicted in blue in schematic dorsal views of the hindbrain and pharyngeal arches. Conserved functional motifs (Krox20, Sox, Meis, Pbx-Hox) present upstream of lamprey and mouse Hox2 genes are shown. Lamprey and mouse enhancers show divergent activities. Comparison between expression domains and conserved motifs leads us to suggest that a putative ancestral vertebrate Hox2 enhancer contained cis-elements for r3/r5 expression (Krox20, Sox) and r4/NC expression (Meis, Pbx-Hox).These scenarios assume that duplication events that gave rise to four Hox clusters in early vertebrates occurred prior to the cyclostome/gnathostome split, as the most parsimonious explanation22,81. However, it is also possible that independent genome duplication events may have occurred in cyclostome and gnathostome lineages (see Holland and Ocampo Daza82 for a recent discussion)

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