Zebrafish use these spiky structures on their pectoral fins to grasp their partners when mating.
image courtesy of Ken Poss

Regenerate or Mate

In zebrafish, spiky structures hinder fin regrowth.

When it comes to sex versus survival, most male zebrafish can’t have it both ways. The fish is either good at mating or good at growing a new fin after an amputation injury. Scientists are now a little closer to understanding why.

A few years ago, Ken Poss, an HHMI early career scientist at Duke University, noticed that female zebrafish were better at regenerating their pectoral fins than male fish. “This type of sexually dimorphic regeneration is pretty unusual,” explains Poss. “It suggests there’s some sort of signaling malfunction in the males.”

Poss and his colleagues discovered that the males had high levels of a protein called Dkk1b in their pectoral fins. Dkk1b is a potent inhibitor of Wnt—a signaling molecule that plays a big role in development, and thus regeneration. The researchers traced the source of Dkk1b to a cluster of needle-like structures, called epidermal tubercles, on the pectoral fins. Males use these spiky growths to grasp their partners when mating. “Normally, [Dkk1b] is regulated in a very precise way during fin regeneration,” Poss says. But when the fins have tubercles, this changes completely.

Poss realized that the production of Dkk1b from epidermal tubercles was short-circuiting the regeneration of pectoral fins. The findings, published in Developmental Cell on October 14, 2013, suggest that zebrafish traded an ancient ability to regenerate tissue for a new way to enhance reproductive success. The good news for zebrafish is that it’s not all or nothing. A certain percentage of males can recover from amputation.

Player for HHMI Bulletin website (based on New HHMI.org Player)
How fin loss affects mating in zebrafish. Credit: From Developmental Cell, 27(1), Junsu Kang, Gregory Nachtrab, Kenneth D. Poss, Local Dkk1 Crosstalk from Breeding Ornaments Impedes Regeneration of Injured Male Zebrafish Fins, Copyright (2013), with permission from Elsevier.

The discovery of this level of control by a signaling inhibitor during tissue regeneration is big news. “It says that these inhibitors are important too,” says Poss. “Putting them in the right places at the right time should be part of making tissue artificially.”