Expression patterns of Hoxa-4 and Hoxa-5 genes along the anterior/posterior axis in transgenic mice. Expressions of Hoxa-4 and Hoxa-5 genes were analyzed by in situ hybridization on sagittal frozen sections of 13-dpc embryos. While the anterior boundary of Hoxa-4 gene expression is located on the first prevertebra (PV1) in transgenic (TG) embryos, it is located on the second prevertebra (PV2) in wild-type (WT) mice. Similarly, the anterior boundary of Hoxa-5 gene expression is located on the third prevertebra (PV3) in TG mice, but it is located on the fourth prevertebra (PV4) in WT mice. drg = dorsal root ganglion. PV1, 2, 3, and 4 corresponds to the final cervical vertebrae C1, C2, C3, and C4, respectively.