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Figure 3 | Frontiers in Zoology

Figure 3

From: New developmental evidence supports a homeotic frameshift of digit identity in the evolution of the bird wing

Figure 3

HoxD expression of digit 2 in a limb that has lost digit 1 remains distinct from digit 1. It is argued that upon loss of digit 1 in evolution, the new most anterior digit, digit 2, may cease to express HoxD10 and HoxD12, thus resembling digit 1. (a, b) Adult morphology of the foot of the rabbit Oryctolagus cuniculus compared to the mouse Mus musculus. In the tetradactyl foot of the rabbit, the long metatarsals and triphalangeal morphology of the digits are typical of digits II-V of mammals. The only missing digit is the biphalangeal digit 1, which in other Glires (such as mouse) has only two phalanges, and a much shorter metatarsal. (c-f) Expression in the embryonic foot of the rabbit and mouse. (c, e) HoxD10 and HoxD12 expression is present in the posterior interdigital mesenchyme (PIDM) of digit 2 of the rabbit foot. (d, f) Expression is absent from the PIDM of digit 1 of the mouse foot, making it clearly distinct from digit II of the rabbit. Scale bars: a, 5—mm; b—5 mm; c, e—500 μm; d, f—500 μm.

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