Figure 3.
Characterization of the LIM homeodomain transcription factor code for misplaced motoneurons after chronic picrotoxin treatment. A, Low-magnification image of cell bodies of dorsally projecting motoneurons labeled with HRP (red) in a 16 μm cross section of crural spinal cord of a picrotoxin-treated embryo. Islet1 immunoreactivity is depicted in green. A misplaced cell expressing Islet1, and therefore not an LMCL motoneuron, is highlighted with an arrow. B, 2× magnification of the area within the box in A. C, Low-magnification image of HRP (red)-positive cell bodies of ventrally projecting motoneurons and Lim1 immunoreactivity (green) in an embryo that underwent light activation by ChR2 in addition to acute picrotoxin treatment. D, 2× magnification image of the area enclosed in the white box in C. E, The bar graph depicting the number of HRP-positive cells expressing the transcription factor incorrect for their D-V projections (Islet1-expressing motoneurons that projected dorsally and Lim1-expressing cells that projected ventrally) as a percentage of all HRP-labeled cells (see Materials and Methods) (*p < 0.025). Light activation by ChR2 reduced the percentage of motoneurons that had made D-V pathfinding errors from ∼20% to several percentage points similar to the control value. Scale bars: A, B, 50 μm. Chr. Picro, Chronic picrotoxin treatment.