The School of Molecular and Cellular Biology at the University of Illinois at Urbana-Champaign

We are conducting studies that will provide insight into why most adult vertebrates, including humans, lose the ability to regenerate their limbs. The same principles that apply to developing systems often hold true for regenerating systems. Our laboratory has a longstanding interest in how vertebrate limb pattern is established during development and regeneration. For instance, the developmental potential of salamander limb buds (newly developing limbs) and regeneration blastemas (regenerating limbs) is changed predictably by application of retinoic acid (Ludolph et al., 1993). Successful vertebrate limb regeneration is accomplished by formation, continued growth, patterning, and differentiation of a regeneration blastema at the cut surface of a limb stump. Mature tissues adjacent to the amputation surface lose their extracellular matrix and cells reenter the cell cycle in preparation for stump repair and regeneration of the lost parts. At the cellular level a regeneration blastema resembles the original embryonic limb bud that gives rise to the mature limb.

Presently we are examining initial cellular and molecular events in the stump following partial hindlimb amputation in premetamorphic and metamorphic Xenopus laevis (African Clawed Frog). Premetamorphic tadpoles can regenerate hindlimb parts, while the ability to regenerate declines as the tadpole undergoes metamorphosis. Tadpole hindlimb regeneration provides a natural loss-of-function system that resembles the typical loss of ability to regenerate in vertebrates. We find that within several premetamorphic stages, the ability to replace lost limb parts is most pronounced at the more distal levels (toe tips) compared to the more proximal levels (Nye et al., 1997; Zimmerman et al., 1999). In addition, we are examining the skeletal elements at the amputation sites to determine whether they are cartilaginous or ossified. Amputation through bone results in less successful regeneration than amputation through cartilage (Nye et al., 1998). This observation may explain, in part, why older limbs do not regenerate as well as younger ones. It is possible that bone tissue cannot contribute to blastema formation as effectively as cartilage. We are studying cellular features of blastemas at the developmental stages and amputation levels where there is predictably “good regeneration” and where there is predictably “poor” regeneration. Blastemas with cellular characteristics most closely resembling limb buds are more likely to regenerate successfully (Wolfe et al., 2000). One hypothesis we are investigating is that the cellular features of “good” and “poor” blastemas can be used to predict whether a particular blastema will regenerate more or less completely.

Knowing the cellular features of blastemas that give rise to more complete regenerates compared to those that will not regenerate gives us insight into possible changes in the expression patterns of certain genes in tadpole hindlimb cells following amputation. From our work and the work of other investigators we know that many of the same genes important during embryonic limb development are expressed again during limb regeneration. Patterning factors like sonic hedgehog, Hox genes and Msx, and growth factors like Fgfs are expressed during limb regeneration. Expression patterns of these genes provide spatially arranged cell signaling centers within limb buds at each developmental stage and similar centers within regeneration blastemas during regeneration. Particular genes may not be expressed or their expression pattern may change when regeneration fails. A second hypothesis we are investigating is that the loss of ability to regenerate is correlated with the change in ability to express developmentally-regulated genes in hindlimb cells following amputation.

Our understanding of the cellular and molecular mechanisms associated with the loss of regenerative ability during frog metamorphosis will form a basis for future studies directed toward extending the ability of Xenopus tadpoles and frogs to replace limb parts.

Representative Publications

Nye, HLD, Cameron JA. 2005. Strategies to Reduce Variation in Xenopus laevis Regeneration Studies. Dev. Dynamics. 234(1):151-8. [Abstract]

Wolfe AD, Crimmins G, Cameron, JA, Henry JJ. 2004. Early Regeneration Genes: Building a Molecular Profile for Shared Expression in Cornea-Lens Transdifferentiation and Hind Limb Regeneration in Xenopus laevis. Dev. Dynamics, 230(4):615-29. [Abstract]

Nye HLD, Cameron JA, Chernoff EAG, Stocum DL. 2003. Regeneration of the urodele limb: a review. Dev. Dynamics 226(2):280-94. [Abstract]

Chernoff EAG, Stocum DL, Nye HLD, Cameron JA. 2003. Urodele spinal cord regeneration and related processes. Dev. Dynamics 226(2):295-307. [Abstract]

Wolfe, A.D., Nye, H.L.D., and Cameron, J.A. 2000. Extent of ossification at the amputation plane is correlated with the decline of blastema formation and regeneration in Xenopus laevis hindlimbs. Develop. Dynamics 218(4):681-97. [Abstract]

Complete Publications List