Identification of an evx1-Dependent Joint-Formation Pathway during FIN Regeneration

Quynh V Ton,M Kathryn Iovine,Henry H Roehl

doi:10.1371/journal.pone.0081240

Abstract

Joints are essential for skeletal flexibly and form, yet the process underlying joint morphogenesis is poorly understood. Zebrafish caudal fins are comprised of numerous segmented bony fin rays, where growth occurs by the sequential addition of new segments and new joints. Here, we evaluate joint gene expression during fin regeneration. First, we identify three genes that influence joint formation, evx1, dlx5a, and mmp9. We place these genes in a common molecular pathway by evaluating both their expression patterns along the distal-proximal axis (i.e. where the youngest tissue is always the most distal), and by evaluating changes in gene expression following gene knockdown. Prior studies from our lab indicate that the gap junction protein Cx43 suppresses joint formation. Remarkably, changes in Cx43 activity alter the expression of joint markers. For example, the reduced levels of Cx43 in the sof b123 mutant causes short fin ray segments/premature joints. We also find that the expression of evx1-dlx5a-mmp9 is shifted distally in sof b123, consistent with premature expression of these genes. In contrast, increased Cx43 in the alf dty86 mutant leads to stochastic joint failure and stochastic loss of evx1 expression. Indeed, reducing the level of Cx43 in alf dty86 rescues both the evx1 expression and joint formation. These results suggest that Cx43 influences the pattern of joint formation by influencing the timing of evx1 expression.

Highlights

The precise location of joints provides both flexibility and form to the vertebrate skeleton
The fin is comprised of multiple bony fin rays or lepidotrichia, and each fin ray is comprised of multiple bony segments separated by fin ray joints
We have shown that morpholino-mediated cx43 knockdown in alf dty86 rescues joint formation, suggesting that the higher levels of cx43 in this mutant contributes to the loss of fin ray joints [7]

Summary

Introduction

The precise location of joints provides both flexibility and form to the vertebrate skeleton. We have shown that morpholino-mediated cx43 knockdown in alf dty86 rescues joint formation, suggesting that the higher levels of cx43 in this mutant contributes to the loss of fin ray joints [7]. We describe the addition of two evx1-dependent joint gene markers that contribute to joint formation: distal-less homeobox-5a (dlx5a) and matrix-metalloproteinase-9 (mmp9).

Results

Conclusion