Figure 1
From: Splicing is dynamically regulated during limb development
Tetrapod limb development (A) Isolated forelimbs from neonatal mouse (left) and chick (right) stained for bone (red) and cartilage (blue). Note differences in digit number, length, and orientation relative to the zeugopod. (B–D) Early limb development is characterized by 3 key stages: ridge, bud, and paddle. (B) The limb is initiated at precise locations along the body axis where retinoic acid (RA), T-Box transcription factors (TBX), and Fgf10 induce the expression of Fgf8 in the distal ectoderm (ridge stage). (C) In the bud stage, genes regulating limb patterning and proliferation are initiated downstream of SHH (turquoise) and AER-Fgfs (pink). (D) In the paddle stage, regionalization of limb modules is mediated by Hox patterning genes: Meis1/2 (stylopod, lavender), Hoxa11 (zeugopod, blue), and Hoxa13 (autopod, pink).
