Figure 3
From: Structural distinctions in BMPs underlie divergent signaling in spinal neurons
A subset of BMPs, not predictable by structure, has orienting ability. (A, B) [d] explants with asymmetrically appended COS-1 cell aggregates expressing myc-tagged BMPs co-labeled with α-TAG-1 (green), α-Lhx2/9 (red) and α-myc (blue). Dashed lines mark appended borders of explants and aggregates. (A) dI axon responses in [d] explants. Arrowheads indicate axons repelled by BMPs. Scale = 50 μm. (B) BMP-stimulated induction of ectopic Lhx2/9 expression in [d] explants. Double-headed arrows mark width of Lhx2/9-expression regions. Scale = 50 μm. (C) Histograms comparing orienting and inductive activities of BMP/TGFβs in [d] explants, grouped according to orientation activity. Green bars indicate angle of axonal orientation (mean ± SEM): BMP9 = 37.7 ± 1.6° (n = 31); BMP7 = 35.0 ± 1.9° (n = 22); BMP4 = 30.6 ± 1.2° (n = 14); BMP2 = 26.8 ± 1.6° (n = 20); GDF6 = 18.8 ± 2.1° (n = 22); BMP5 = 16.1 ± 1.8° (n = 28); dorsalin-1 = 11.8 ± 2.8° (n = 15); BMP6 = 7.0 ± 2.2° (n = 24); GDF5 = 6.6 ± 2.2° (n = 20); GDF7 = 3.7 ± 1.5° (n = 19); TGFβ3 = −2.1 ± 1.6° (n = 11); TGFβ2 = 0.56 ± 2.8° (n = 9); Activin A = −6.0 ± 1.2° (n = 21); pMT23 = −3.5 ± 1.6° (n = 14). Student’s t tests: Axon orientation responses to BMP5 and BMP6 were significantly different (P = 0.0022) with responses to BMP7 significantly different from both BMP5 and BMP6 (P <0.0001), revealing three distinct levels of orienting activity in the BMP5/6/7 subgroup. Red bars indicate Lhx2/9 induction (mean ± SEM): BMP9 = 203 ± 26% (n = 11); BMP7 = 174 ± 33% (n = 6); BMP4 = 175 ± 26% (n = 10); BMP2 = 158 ± 14% (n = 11); GDF6 = 173 ± 15% (n = 4); BMP5 = 184 ± 31% (n = 7); dorsalin-1 = 205 ± 29% (n = 7); BMP6 = 153 ± 18% (n = 7); GDF5 = 198 ± 20% (n = 12); GDF7 = 215 ± 18% (n = 14); TGFβ3 = −8 ± 6% (n = 10); TGFβ2 = −1 ± 4% (n = 9); Activin A = −5 ± 7% (n = 16). Inductive activity is not statistically different among the BMPs (P = 0.5773, ANOVA). (D) Phylogenetic tree of BMPs and select other members of the TGFβ superfamily. BMPs with robust orienting activity are highlighted in green. Dashed lines between (C) and (D) highlight differing orienting activities yet close structural relationship of the BMP5/6/7 subgroup.