Potassium channels and pigment pattern formation
An inward rectifier is a potassium channel that tends to be more permeable to ions flowing toward the cytoplasm.4 In zebrafish, the inward rectifier Kir7.1, encoded by Kcnj13, is required to establish the adult pigment pattern.5 The jaguar/obelix mutant shows that one channel gene can change where pigment cells sit without changing how they develop.1
- Earliest held
- 2006, Iwashita M, Watanabe M, Ishii…
- Most discussed in
- Pigment pattern in jaguar/obelix zebrafish is…, 2006
- In the library
- 72 passages in 22 works
- Rewritten
- 2026-10-13
The jaguar/obelix mutant
Iwashita and colleagues (2006) studied the zebrafish jaguar/obelix mutant, which has broader stripes than wild-type fish.1 They reported that pigment cell development is normal in this mutant but the distribution of the cells is altered.1 For that reason they treated it as a good system for studying how pigment patterns form. Silic and Zhang (2023) describe the wild-type pattern as alternating rows of melanophores and xanthophores mixed with iridophores.9 They state that local and long-range interactions among these cells are essential to forming the stripes.9
Cloning and cell behaviour
The same group used positional cloning and identified the Kir7.1 gene as responsible for the altered distribution of pigment cells.2 They found amino acid changes in the conserved region of Kir7.1 in the mutant alleles. Patch-clamp experiments showed that each change affected K+ channel activity.2 Injection of a bacterial artificial chromosome with the wild-type Kir7.1 sequence rescued the jaguar/obelix fish.2 They also reported that jaguar/obelix melanophores fail to aggregate or disperse melanosomes correctly in response to neural signals.3 From this they proposed an explanation for the pattern change based on defects in signal transduction.3
What an inward rectifier is
Pillozzi and Becchetti (2012) define an inward rectifier as a channel that tends to be more permeable to ions flowing toward the cytoplasm.4 They add that not every channel in the KIR structural family shows prominent inward rectification.4 Cervera, Alcaraz and Mafe (2016) describe inward-rectifying channels as allowing large inward currents at potentials more negative than the equilibrium potential.6 In their model of transitions between hyperpolarized and depolarized states, the ratio of outward to inward conductance regulated the transition. Cells that express the two channel types differently may therefore show different membrane potentials.7 These two works do not concern pigment cells directly.
Wider bioelectric context
Perathoner and colleagues (2014) noted that KIR channels have been shown to take part in patterning in vertebrates and invertebrates.5 They cited Drosophila Irk2 wing defects and human Kir2.1 craniofacial and digital defects alongside zebrafish Kcnj13.5 Their own finding concerned a different class, the K2P channel kcnk5b, whose gain-of-function mutations overgrow the fins.5 McMillen and colleagues (2021) argue that bioelectric signalling differs from growth factor signalling because information is carried by physiological parameters set by many ion channels, not by specific proteins.8 Silic and Zhang (2023) note that several pigment mutants affect ion regulators.9 Two of them, albino and golden, are solute carrier genes rather than channels.9
The zebrafish jaguar/obelix mutant has broader stripes than wild-type fish. In this mutant, the development of pigment cells is normal but their distribution is altered
Iwashita M, Watanabe M, Ishii M, Chen T, Johnson SL…, 2006 · Pigment pattern in jaguar/obelix zebrafish is caused by a Kir7.1 mutation… · open at passage 0we identified amino acid changes in the conserved region of Kir7.1, each of which affected K+ channel activity as demonstrated by patch-clamp experiments.
Iwashita M, Watanabe M, Ishii M, Chen T, Johnson SL…, 2006 · Pigment pattern in jaguar/obelix zebrafish is caused by a Kir7.1 mutation… · open at passage 0We further demonstrate that the melanophores of jaguar/obelix mutants fail to aggregate or disperse melanosomes correctly in response to neural signals.
Iwashita M, Watanabe M, Ishii M, Chen T, Johnson SL…, 2006 · Pigment pattern in jaguar/obelix zebrafish is caused by a Kir7.1 mutation… · open at passage 5The term inward rectifier applies to those ion channels that tend to be more permeable to ions flowing toward the cytoplasm.
Pillozzi S, Becchetti A, 2012 · Ion channels in hematopoietic and mesenchymal stem cells · open at passage 7In zebrafish establishment of the adult pigmentation pattern requires the function of Kcnj13 (Kir7.1) [49].
Perathoner S, Daane JM, Henrion U, Seebohm G, Higdon CW…, 2014 · Bioelectric signaling regulates size in zebrafish fins · open at passage 18The inward-rectifying channels allow large inward currents at potentials more negative than the equilibrium potential
Cervera J, Alcaraz A, Mafe S, 2016 · Bioelectrical Signals and Ion Channels in the Modeling of Multicellular… · open at passage 40Remarkably, the transition characteristics can be regulated by the conductance ratio Gout/Gin14, which suggests that cells expressing differently the outward and inward rectifying channels characteristics
Cervera J, Alcaraz A, Mafe S, 2016 · Bioelectrical Signals and Ion Channels in the Modeling of Multicellular… · open at passage 9Bioelectric signaling fundamentally differs from growth factor-based signaling in that information is encoded not by specific proteins but by physiological parameters established by the action of many diverse ion channels.
McMillen P, Oudin MJ, Levin M, Payne SL, 2021 · Beyond Neurons: Long Distance Communication in Development and Cancer · open at passage 10Among many mutant zebrafish lines with altered pigmentation patterns, several are mutations of ion regulators, suggesting that ion-channel-mediated bioelectric signals play important roles in pigmentation patterning.
Silic MR, Zhang G, 2023 · Bioelectricity in Developmental Patterning and Size Control: Evidence and… · open at passage 24