New publication! The actin cytoskeleton plays multiple roles in structural colour formation in butterfly wing scales
20 May 2022
In a paper published in Nature Communications, we identify how butterflies are able to grow intricate nanostructures on their wings, all controlled by a single cell. These nanostructures are responsible for an iridescent blue colour on the wings.
A Heliconius sara butterfly, of the type we investigated, showing the structural iridescent blue colour
Vicky Lloyd firstly used confocal microscopy with fluorescent probes that labelled the actin cytoskeleton and chitin (a major constituent of the cuticle) to chart how the scale forms through development. She showed that scales that will become blue have more ridges on their surface, and this is controlled by having more actin filaments.
To see what was happening in more detail, we had to go beyond the limits of normal light microscopy. So Vicky went to work at the Central Laser Facility on their super-resolution STED microscope.
Victoria Lloyd with microscopy scientist Esther Garcia at the Central Laser Facility.
We found that the actin cytoskeleton was being extensively re-organised throughout development in a way that prefigured the formation of different structural elements of the scale.
Merge of actin (phalloidin, green) and chitin (CBD-TMR, magenta). Cartoon insets highlight the purported location of the actin filaments (green) and the associated cuticle structure (magenta). A At 63% development actin can be seen below the scale ridges. B At 69% development actin filaments are patterned along the side of a ridge, appearing like the microribs of adult scales. C At 75% development, the main scale body is filled with square ‘blocks’ of actin within the window regions in between the crossribs. Scale bars: (A–C) 10 μm; (Ai, Bi, Ci) 2 μm.
Vicky then went on to show that disrupting actin, after the ridges have formed but before the nanostructures form, led to an almost complete loss of structural colour. Showing that actin is essential for nanostructure (and so structural colour) formation.
This work is an important step in understanding how biological systems make and control structural colours. Something that humans have been trying to replicate for decades, with limited success.