Expression of Hoxb13 and Hoxc10 in developing and regenerating axolotl limbs and tails

The expression of Hox complex genes in correct spatial and temporal order i s critical to patterning of the body axis and limbs during embryonic develo pment. In order to understand the role such genes play in appendage regener ation, we have compared the expression of two 5' Hox complex genes: Hoxb13 and Hoxc10 during development and regeneration of the body axis and the lim bs of axolotls. In contrast to higher vertebrates, Hoxb13 is expressed not only in the tip of the developing tail, but also in the distal mesenchyme o f developing hind limbs, and at low levels in developing forelimbs. Hoxc10 is expressed as two transcripts during both development and regeneration. T he short transcript (Hoxc10S) is expressed in the tip of the developing tai l, in developing hind limbs, and at low levels in developing forelimbs. The long transcript (Hoxc10L) is expressed in a similar pattern, with the exce ption that no expression in developing forelimbs could be detected. Hoxb13 and both transcripts of Hosc10 are expressed at high levels in the regenera ting spinal cord during tail regeneration, and in both regenerating hind li mbs and forelimbs. The up-regulation of expression of these genes during fo relimb regeneration, relative to the very low levels of expression during f orelimb development, suggests that they play a critical and perhaps unique role in regeneration. This is particularly true for Hoxc10L, which is not e xpressed during forelimb development, but is expressed during forelimb rege neration; thus making it the first truly "regeneration-specific" gene trans cript identified to date. (C) 2001 Academic Press.