Type XII collagen up-regulation is associated with regeneration of fully developed but not embryonic limbs of the salamander and newt

Abstract

Monoclonal antibodies (mAbs) MT1 and MT2 provided the opportunity to compare developing and regenerating limbs with regard to the temporal and spatial appearance of the developmentally regulated, extracellular matrix (ECM) proteins tenascin (TN) and type XII collagen (col XII), respectively. In limb buds and in regenerates of both limb buds and mature limbs, mAb MT1 reactivity was seen within the ECM between mesenchyme cells and as a layer subjacent to the ectoderm and wound epithelium. In contrast, reactivity of mAb MT2 was absent from limb buds or regenerating limb buds, but was strong in the distal limb stump and blastema of regenerating mature limbs. At differentiation stages of limb development, TN and col XII were seen in association with perichondrium, myotendinous junctions, and tendons, typical of their distributions in mature limbs. In situ hybridization with a probe that recognizes transcripts of both the long form and the alternatively spliced short form of the alpha chain of type XII collagen (alpha col XII) confirmed that mAb MT2 reactivity represented alpha col XII expression and further showed that neither form of alpha col XII mRNA is expressed in early limb buds of chicken or urodele embryos. Thus, when the expression patterns of antigens are compared during limb development and regeneration, both similarities and differences are revealed. The results are consistent with the view that col XII has a role in the regeneration of mature limbs but not in the development or regeneration of embryonic limbs. J. Exp. Zool. 279:71-80, 1997. © 1997 Wiley-Liss, Inc.