Survival of Hoxa13 Homozygous Mutants Reveals a Novel Role in Digit Patterning and Appendicular Skeletal Development

The loss of HOXA13 function severely disrupts embryonic limb development. However, because embryos lacking HOXA13 die by mid-gestation, the defects present in the mutant limb could arise as a secondary consequence of failing embryonic health. In our analysis of the mutant Hoxa13(GFP) allele, we identified a surviving cohort of homozygous mutants exhibiting severe limb defects including: missing phalanx elements, fusions of the carpal/tarsal elements, and significant reductions in metacarpal/metatarsal length. Characterization of prochondrogenic genes in the affected carpal/tarsal regions revealed significant reduction in Gdt5 expression, whereas Bmp2 expression was significantly elevated. Analysis of Gdt5 mRNA localization also revealed diffuse expression in the carpal/tarsal anlagen, suggesting a role for HOXA13 in the organization of the cells necessary to delineate individual carpal/tarsal elements. Together these results identify Gdf5 as a potential target gene of HOXA13 target gene and confirm a specific role for HOXA13 during appendicular skeletal development. Developmental Dynamics 239:446-457, 2010. (C) 2009 Wiley-Liss, Inc.