Fig. 1.

Loss of function of Hox5 paralogous genes results in anterior forelimb defects. (A–G) Skeletal analysis of control and Hox5 triple-mutant forelimbs at E18.5. The scapula is reduced in Hox5 triple mutants compared with controls, as observed for Hoxa5 single mutants (A–C, red arrows). The stylopod is reduced or truncated only in embryos with a phenotype in the radius (B and C, blue arrow). The radius of mutant forelimbs is missing or severely truncated (B and C, black asterisk). (D–G) The most anterior digit develops abnormally in Hox5 mutants compared with controls. Digit 1 is often missing (E) or triphalangeal (F and G, green asterisk). Less frequently, Hox5 mutants also have a bifurcated digit 2 (G, black arrow). Digit phenotypes do not correlate with the severity of stylopod/zeugopod defects. (H) Table summarizing forelimb phenotypes of Hox5 mutant forelimbs. (I) Compound mutants deficient for as many as five of the six Hox5 alleles do not exhibit limb defects. (J and K) Hindlimb development is not affected in Hox5 mutants.