Control of growth and gut maturation by &ITHoxD&IT genes and the associated lncRNA &ITHaglr&IT

During embryonic development, Hox genes participate in the building of a functional digestive system in metazoans, and genetic conditions involving these genes lead to important, sometimes lethal,growth retardation. Recently, this phenotype was obtained after deletion of Haglr, the Hoxd antisense growth-associated long non-coding RNA (IncRNA) located between Hoxd1 and Hoxd3. In this study, we have analyzed the function of Hoxd genes in delayed growth trajectories by looking at several nested targeted deficiencies of the mouse HoxD cluster. Mutant pups were severely stunted during the suckling period, but many recovered after weaning. After comparing seven distinct HoxD alleles, including CRISPR/Cas9 deletions involving Haglr, we identified Hoxd3 as the critical component for the gut to maintain milk-digestive competence. This essential function could be abrogated by the dominant-negative effect of HOXD10 as shown by a genetic rescue approach, thus further illustrating the importance of posterior prevalence in Hox gene function. A role for the IncRNA Haglr in the control of post-natal growth could not be corroborated.