Shape-shifting cells behind stripes of zebrafish

Researchers, including Indian-origin scientists, have discovered how the three major pigment cell types - black, reflective silvery, and yellow cells - arise and behave to form the 'zebra' pattern in zebrafish, a small fresh water fish.

The yellow cells undergo dramatic changes in cell shape to tint the stripe pattern of zebrafish, the findings showed.

"We were surprised to observe such cell behaviours, as these were totally unexpected from what we knew about colour pattern formation," said first author of the study Prateek Mahalwar from Max Planck Institute for Developmental Biology in Germany.

Both the silvery and yellow cells are able to switch cell shape and colour, depending on their location, the findings showed.

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 colouration 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," Nusslein-Volhard from Max Planck Institute noted.

The findings appeared in the journal Science.