Genetic reduction of BMP signaling and Ark2C in motor pools reproduces the dorsal forelimb innervation defects.

<p>(A–B) Confocal images of whole-mount IF with anti-GFP showing motor neuron innervation of the forelimb in HB9-eGFP embryos from crosses between <i>Ark2C</i>^+/−;<i>BMPRII</i>^+/− and <i>Ark2C</i>^+/− (A) and between <i>Ark2C</i>^+/−;<i>Smad8</i>^+/− and <i>Smad8</i>^−/− (B). Arrows as in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001538#pbio-1001538-g004" target="_blank">Figures 4F</a> and <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001538#pbio.1001538.s007" target="_blank">S7A</a>; scale bars = 250 µm. (C) Quantification of the innervation at E13.5 shown as percentages of forelimbs, each phenotypic classification as described; N, number of forelimbs. (D) The population spread of average hang time in the cage lid test for each genotype. Ark2C Smad8 littermates, mix of <i>Ark2C^+/+</i>:<i>Smad8</i>^+/−, <i>Ark2C^+/+</i>:<i>Smad8</i>^−/−. <i>Ark2C</i>^+/−:<i>Smad8</i>^+/−. ** <i>p</i><0.01. (E) Transverse section of E15.5 <i>Smad8</i>^+/− embryo at brachial level after X-gal staining showing Smad8 expression in bone, cartilage, DRG, and motor pools. Numbers as in “The Atlas of Mouse Development” <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001538#pbio.1001538-Kaufman1" target="_blank">[75]</a> 31*, 32*, 54* on pp 266–267 and 28, 31, 34, 39, 42, 43, 49, 54 on pp 268–269; mm, muscle mass; MN, motor neurons. (F) Sagittal and transverse (C′ and C″) vibrotome sections of the spinal cord from a <i>Smad8</i>^+/− embryo stained with X-gal showing Smad8 expression in motor pools or co-stained with antibody against FoxP1. White arrowhead, DRG; blue, cytoplasmic X-gal stain of Smad8 expression; brown, nuclear FoxP1 expression; sagittal section, dorsal towards top; scale bars = 100 µm. Dotted line indicates position of sagittal section in the first panel; first rib is indicated by black arrowhead.