Zebrafish, a small fresh water fish, owes its name to a striking pattern of blue stripes alternating with golden stripes.
Three major pigment cell types, black cells, reflective silvery cells, and yellow cells emerge during growth in the skin of the tiny juvenile fish and arrange as a multilayered mosaic to compose the characteristic color pattern.
Zebrafish owe their name to a repetitive pattern of blue stripes and golden interstripes parallel to the body axis.
Prateek Malhawar / Max-Planck-Institut für Entwicklungsbiologie
Yellow pigment cells, right panel, provide yellow colour to the pattern and cover the skin in two distinct shapes.
Prateek Malhawar / Max-Planck-Institut für Entwicklungsbiologie
While it was known that all three cell types have to interact to form proper stripes, the embryonic origin of the pigment cells that develop the stripes of the adult fish has remained a mystery till now. Scientists of the Max Planck Institute for Developmental Biology have now discovered how these cells arise and behave to form the zebra pattern.
Beauty in the living world amazes poets, philosophers and scientists alike. Nobel prize laureate Christiane Nüsslein-Volhard, Director of the Department for Genetics at the Max Planck Institute for Developmental Biology, has long been fascinated by the biology behind the colour patterns displayed by animals. Her group uses zebrafish as a model organism to study the genetic basis of animal development.
New research by Nüsslein-Volhard’s laboratory published in Science shows that the yellow cells undergo dramatic changes in cell shape to tint the stripe pattern of zebrafish. “We were surprised to observe such cell behaviours, as these were totally unexpected from what we knew about colour pattern formation”, says Prateek Mahalwar, first author of the study.
The study builds on a previous work from the laboratory, which was published in June this year in Nature Cell Biology (NCB), tracing the cell behaviour of silvery and black cells. Both studies describe diligent experiments to uncover the cellular events during stripe pattern formation. Individual juvenile fish carrying fluorescently labelled pigment cell precursors were imaged every day for up to three weeks to chart out the cellular behaviours.
This enabled the scientists to trace the multiplication, migration and spreading of individual cells and their progeny over the entire patterning process of stripe formation in the living and growing animal. "We had to develop a very gentle procedure to be able to observe individual fish repeatedly over long periods of time. So we used a state of the art microscope which allowed us to reduce the adverse effects of fluorescence illumination to a minimum," says Ajeet Singh, first author of the earlier NCB study.
Surprisingly, the analysis revealed that the three cell types reach the skin by completely different routes: A pluripotent cell population situated at the dorsal side of the embryo gives rise to larval yellow cells, which cover the skin of the embryo. These cells begin to multiply at the onset of metamorphosis when the fish is about two to three weeks old.
However, the black and silvery cells come from a small set of stem cells associated with nerve nodes located close to the spinal cord in each segment. The black cells reach the skin migrating along the segmental nerves to appear in the stripe region, whereas the silvery cells pass through the longitudinal cleft that separates the musculature and then multiply and spread in the skin.
Brigitte Walderich, a co-author of the Science paper, who performed cell transplantations to trace the origin of yellow cells, explains: “My attempt was to create small clusters of fluorescently labelled cells in the embryo which could be followed during larval and juvenile stages to unravel growth and behaviour of the yellow cells. We were surprised to discover that they divide and multiply as differentiated cells to cover the skin of the fish before the silvery and black cells arrive to form the stripes.”
A striking observation is that both the silvery and yellow cells are able to switch cell shape and colour, depending on their location. The yellow cells compact to closely cover the dense silvery cells forming the light stripe, colouring it golden, and acquire a loose stellate shape over the black cells of the stripes. The silvery cells thinly spread over the stripe region, giving it a blue tint.
They switch shape again at a distance into the dense form to aggregate, forming a new light stripe. These cell behaviours create a series of alternating light and dark stripes. The precise superposition of the dense form of silvery and yellow cells in the light stripe, and the loose silvery and yellow cells superimposed over the black cells in the stripe cause the striking contrast between the golden and blue coloration of the pattern.
The authors speculate that variations on these cell behaviours could be at play in generating the great diversity of colour patterns in fish. “These findings inform our way of thinking about colour pattern formation in other fish, but also in animals which are not accessible to direct observation during development such as peacocks, tigers and zebras”, says Nüsslein-Volhard.
Nadja Winter | Max-Planck-Institut
About injured hearts that grow back - Heart regeneration mechanism in zebrafish revealed
10.02.2016 | Universität Ulm
Chemical cages: New technique advances synthetic biology
10.02.2016 | Arizona State University
Atomic clock experts from the Physikalisch-Technische Bundesanstalt (PTB) are the first research group in the world to have built an optical single-ion clock which attains an accuracy which had only been predicted theoretically so far. Their optical ytterbium clock achieved a relative systematic measurement uncertainty of 3 E-18. The results have been published in the current issue of the scientific journal "Physical Review Letters".
Atomic clock experts from the Physikalisch-Technische Bundesanstalt (PTB) are the first research group in the world to have built an optical single-ion clock...
The University of Würzburg has two new space projects in the pipeline which are concerned with the observation of planets and autonomous fault correction aboard satellites. The German Federal Ministry of Economic Affairs and Energy funds the projects with around 1.6 million euros.
Detecting tornadoes that sweep across Mars. Discovering meteors that fall to Earth. Investigating strange lightning that flashes from Earth's atmosphere into...
Physicists from Saarland University and the ESPCI in Paris have shown how liquids on solid surfaces can be made to slide over the surface a bit like a bobsleigh on ice. The key is to apply a coating at the boundary between the liquid and the surface that induces the liquid to slip. This results in an increase in the average flow velocity of the liquid and its throughput. This was demonstrated by studying the behaviour of droplets on surfaces with different coatings as they evolved into the equilibrium state. The results could prove useful in optimizing industrial processes, such as the extrusion of plastics.
The study has been published in the respected academic journal PNAS (Proceedings of the National Academy of Sciences of the United States of America).
Exceeding critical temperature limits in the Southern Ocean may cause the collapse of ice sheets and a sharp rise in sea levels
A future warming of the Southern Ocean caused by rising greenhouse gas concentrations in the atmosphere may severely disrupt the stability of the West...
Indications of light-induced lossless electricity transmission in fullerenes contribute to the search for superconducting materials for practical applications.
Superconductors have long been confined to niche applications, due to the fact that the highest temperature at which even the best of these materials becomes...
09.02.2016 | Event News
02.02.2016 | Event News
26.01.2016 | Event News
10.02.2016 | Life Sciences
10.02.2016 | Earth Sciences
10.02.2016 | Physics and Astronomy