Xenopus laevis gelatinase B (Xmmp-9): development, regeneration, and wound healing

It has been argued that matrix metalloproteinases play important roles in cellular differentiation and regeneration in certain systems. While studying changes in gene expression associated with the phenomena of cornea/lens transdifferentiation ("lens regeneration"), which takes place in the larva of Xenopus laevis, we identified the Xenopus gelatinase B gene. The open reading frame is homologous to other gelatinase B genes identified in other species and encodes all of the domains characteristic of this protein. Xenopus gelatinase B (Xmmp-9) is first expressed during early tail-bud stages in a subset of mesodermal cells scattered throughout the body. Expression is also seen in the peripheral tissues of the developing liver diverticulum, the hindgut/cloaca, and the paired caudal vein, and its dorsal branch in the larval tail. Given the significant role of matrix metalloproteinases in degrading components of the extracellular matrix, Xmmp-9 expression may be important in the morphogenesis of these structures. Xmmp-9 expression was also examined during the processes of cornea/lens transdifferentiation, epithelial wound healing, and limb regeneration in Xenopus larvae. Although Xmmp-9 is expressed very early during cornea/lens transdifferentiation, expression is restricted to the site of the peripheral wound created by removal of the original lens, which triggers transdifferentiation. Expression was not found in the central, uninjured area of the cornea where transdifferentiation takes place. Therefore, Xmmp-9 does not appear to play an important role in cornea/lens transdifferentiation. Xmmp-9 expression is associated with other epithelial wounds, indicating that gelatinase B is expressed in the general context of wound healing in Xenopus. Finally, Xmmp-9 is expressed in the ectoderm and mesoderm at the tip of the amputated limb, very early during limb regeneration, where it is argued to play a role in this process.