New insights into the functional role of Hoxc genes in the limb ectoderm

Abstract

To clarify the genetic networks controlling limb elongation, we have performed the temporal expression profiling of the distal mouse limb ectoderm. Comparison between successive stages showed that major changes occurred between E9.5 and E10.5 (295 differentially expressed genes) while only a few genes changed between E10.5 and 11.5 and between E11.5 and E12.5. Interestingly, several members of the HoxC cluster were among the identified regulated genes and the RNA-seq tracks revealed a pattern of Hoxc gene collinear activation in the distal limb ectoderm which was confirmed by in situ hybridization. Since it is known that Hoxc13 is involved in hair and nail development and that HOXC13 is causative for the Pure Hair and Nail Ectodermal Dysplasia, we decided to further study the function of Hoxc genes in the limb ectoderm (Godwin & Capecchi, 1998; Lin et al., 2012). We observed that, in the complete absence of the HoxC cluster, development of the nails was absent or severely impaired and we are currently characterizing the cellular and molecular features of the mutant digit tips. We also sought to investigate the accessible chromatin in the HoxC landscape using ATAC-seq and identified two putative regulatory regions located 5' of the cluster. Because the hoof, just a modified nail, is a major and necessary innovation in the evolution of a cursorial lifestyle, we also seek to unravel the possible role Hoxc genes may have played in the nail/claw/hoof transition as a way to generate a variety of evolutionary changes in distal limb appendages.