Oxidation of PTPs is important for zebrafish embryo caudal fin regeneration

Alexander James Hale, Jeroen den Hertog and their collaborators Wei Wu and Simone Lemeer from Utrecht University have shown that during caudal fin regeneration in the zebrafish embryo certain protein-tyrosine phosphatases are oxidized. They also show the importance of one of these protein-tyrosine phosphatases, Shp2, in caudal fin regeneration, since zebrafish embryos lacking this protein are unable to regenerate their caudal fins. These findings were published as a scientific article in the journal Scientific Reports.

Caudal fin regeneration
Zebrafish, unlike humans, have the capacity to regenerate lost tissues and organs, such as their caudal fin. Caudal fin regeneration in the zebrafish is studied by amputating the tip of the caudal fin and studying the various processes that are involved in regeneration. Many signaling pathways are thought to be important for regeneration of the caudal fin, but it is unclear how this complex process is initiated.

H₂O₂
Hydrogen peroxide (H₂O₂), an oxidizing molecule, is rapidly produced after caudal fin amputation and is essential for regeneration. Previous research has shown that H₂O₂ is able to act as a second messenger molecule by regulating various signaling pathways. However, this function of H₂O₂ was never studied in regeneration.

Protein-tyrosine phosphatases
Protein-tyrosine phosphatases (PTPs) are enzymes that are involved in the regulation of various signaling pathways, that in turn are involved in fundamental cellular processes, including proliferation, differentiation and cell-cell adhesion. PTPs can be oxidized by H₂O₂.

Therefore, the Den Hertog group hypothesized that the H₂O₂ produced after caudal fin amputation oxidizes (certain) PTPs, which would have various downstream effects involved in caudal fin regeneration.

Differential oxidation
The Den Hertog group tested this hypothesis by identifying all PTPs that are present in the caudal fin using an oxPTP-specific antibody and mass spectrometry in collaboration with Wei Wu and Simone Lemeer from Utrecht University. In this tour de force experiment, they found 33 PTPs that are present in the caudal fin. Only 8 of them are oxidized after caudal fin amputation, which shows that only certain PTPs respond to H₂O₂ after amputation and that these PTPs might be involved in caudal fin regeneration.

PTP Shp2 is involved in caudal fin regeneration
To test this, they generated zebrafish lacking one of the oxidized PTPs (Shp2), and zebrafish lacking one of the PTPs that was not oxidized (Rptpα). Caudal fin amputation in these zebrafish embryos showed that the zebrafish lacking Shp2 were unable to regenerate their caudal fin, whilst zebrafish lacking Rptpα regenerated their caudal fin like wildtype zebrafish embryos.

Conclusion
These results show that H₂O₂ produced after caudal fin amputation oxidizes certain PTPs in the caudal fin, and that these PTPs are likely important for caudal fin regeneration. It will be interesting to find out whether the other oxidized PTPs are also essential to caudal fin regeneration, which signaling pathways are regulated by these PTPs, and how they are involved in the regeneration of the caudal fin.

Prof. dr. Jeroen den Hertog is group leader and scientific director at the Hubrecht Institute (KNAW) in Utrecht and professor of Molecular Developmental Zoology at Leiden University.

Differential oxidation of protein-tyrosine phosphatases during zebrafish caudal fin regeneration (PDF)
Scientific Reports 2017