Figure 1. 5’Hoxd genes (d11-d13) act in concert to regulate polarity of limb condensation order in mouse.

(A) Schematic of limb condensation appearance order in wildtype non-urodele tetrapods (such as mouse), with postaxial dominance (posterior elements form first) compared to wildtype urodeles, with preaxial dominance (anterior elements form first). Forelimb example shown; final adult skeletal pattern shows idealized 5-digit phalangeal formula for tetrapod ground state. Red indicates axial dominance; A, anterior; P, posterior limb bud. Modified from Shubin et al.[17] and from Xu et al.[36].

(B) NogginLacZ staining of forming limb condensations ranging from stage E11.25 – E12.5 in control (WT or 5’HoxdΔ/+) and 5’HoxdΔ/Δ forelimb (FL) and hindlimb (HL) buds. Posterior zeugopod elements form first in WT followed by alternating digit condensations beginning with digit 4 (4–2-5–3 order), whereas anterior elements form first in 5’HoxdΔ/Δ and digit condensations begin with digit 2 (2–4-3–5 order).

(C) NogginLacZ staining of forming limb condensations in single Hoxd11^−/− (KO) and Hoxd13^−/− (KO) mutant limb buds compared with control and 5’HoxdΔ/Δ. Posterior elements condense first in the single mutants, similar to control, in contrast to 5’HoxdΔ/Δ. (See also Figure S1). In all figure panels of NogginLacZ staining (in Figures 1, 2, 3C–D), limb buds are shown with anterior to left – posterior to right and distal at top of panel, and with U=ulna, R=radius, T=tibia, F=fibula, digits 1–5 = d1 - d5. All skeletal elements are annotated in the rightmost panel, latest stage limb bud shown. In other panels, only newly appearing elements are annotated with arrows. See also Figure S1.