Distinct regulation of Hox genes by Polycomb Group genes in a crustacean

Non-insect crustaceans exhibit tremendous body plan diversity. The evolution of diverse patterns of Hox gene expression has been implicated as a primary driver of body plan evolution between crustacean groups, but the mechanisms underlying Hox regulatory evolution remain unknown. We identify Polycomb and Trithorax Group proteins, crucial for proper Hox regulation across bilaterians, in the genome of the amphipod crustacean Parhyale hawaiensis, and demonstrate their essential functions in crustacean Hox regulation and embryonic development using CRISPR-Cas9 mutagenesis. Examination of Hox misexpression patterns between individual Hox genes with respect to timing, tissue, and PcG mutant gene in mutant embryos reveals that each crustacean Hox gene follows its own idiosyncratic regulatory mechanism. These results suggest a distinct regulation of Hox genes that may have enabled crustacean body plan evolution. Primary Findings- The genome of the amphipod crustacean Parhyale hawaiensis contains all core Polycomb Group (PcG) and Trithorax Group (TrxG) proteins - CRISPR-Cas9 mutagenesis of PcG proteins induces homeotic transformations and misexpression of Hox genes that differ from similar experiments in insects - PcG knockout embryos show proper initiation of Hox expression boundaries at early developmental stages - Each of the three posterior Hox genes in Parhyale displays distinct patterns of misexpression in response to PcG knockout - Hox regulation appears to occur via different mechanisms in the nervous system vs. limbs - PcG phenotypes reveal the potential for distinct layers of Hox regulation in crustaceans O_FIG O_LINKSMALLFIG WIDTH=193 HEIGHT=200 SRC="FIGDIR/small/485719v1_ufig1.gif" ALT="Figure 1"> View larger version (59K): org.highwire.dtl.DTLVardef@7508a7org.highwire.dtl.DTLVardef@18b0c2dorg.highwire.dtl.DTLVardef@1cc602corg.highwire.dtl.DTLVardef@bdf7fc_HPS_FORMAT_FIGEXP M_FIG C_FIG