Fig. 1. The expression pattern of Hox10 paralogs. (A) Schematic showing the columnar organization, peripheral targets and transcription factor expression of motoneurons in the thoracic and lumbar spinal cord of E13.5 mouse embryos (Kania et al., 2000; Sharma et al., 2000; Sharma et al., 1998; Thaler et al., 2004; Tsuchida et al., 1994). (B) Whole-mount in situ images showing Hoxa10, Hoxc10 and Hoxd10 expression in the spinal cord of E13.5 embryos (ventral view, rostral is toward the top). T9, thoracic segment 9; L1 and L5, lumbar segments 1 and 5. (C) Double labeling of E11 spinal cord with in situ probes for Hox10 genes and anti-Isl1, which labels all motoneurons and sensory neurons at this stage. Note that at this early stage, Hoxc10 and Hoxd10 are expressed throughout the motoneuron domain, whereas Hoxa10 is expressed only in a very focal ventral region, most likely the V3 interneuron domain (arrow). Panels showing Hoxa10, Hoxc10 and Hoxd10 are from adjacent sections of mid-lumbar cord. D, dorsal root ganglion; M, motoneuron domain. (D,E) Cross-sections through the middle of lumbar segments L2-L5 of E13.5 spinal cord, triple labeled for Hoxc10 (D) or Hoxd10 (E), Isl1 and Lim1. By this stage, Isl1 labels mMMC (arrow; compare with Lim3 staining in Fig. 4B) and mLMC (m) motoneurons, Lim1 labels motoneurons in the lLMC (l), and Hoxc10 and Hoxd10 are expressed broadly throughout much of the ventral two-thirds of the spinal cord. Although the overall expression patterns of Hoxc10 and Hoxd10 are similar, they appear to be in different subpopulations of motoneurons. Both genes, however, are expressed more strongly in lLMC and mMMC than in mLMC. In situ images were pseudocolored blue on a white background in the left columns, and blue on a black background in the merged images. Images in D and E are from adjacent sections. Scale bars: 100 µm.