MICROTUBULES AND MICROFIBRILS IN MORPHOGENESIS OF THE SCALE CELLS OF EPHESTIA KÜHNIELLA

Abstract

The development of scale cells in insects has been studied from the appearance of the first cytoplasmic projection which forms the scale rudiment. This rudiment contains numerous longitudinally oriented microtubules throughout. Immediately under its outer surface lie a series of adjacent but distinct bundles of longitudinally oriented circa 60-A fibrils with a circa 120-A center-to-center spacing. As the rudiment broadens, the microtubules become distributed near the surface. The rudiment finally becomes extremely broad and flattened. Fibril bundles are now widely separated and equally spaced. They still lie immediately below the cell surface. Then the cytoplasm protrudes midway between each fibril bundle to form longitudinal ridges and the major shape changes of the scale have been achieved. The final pattern can thus be related to the cytoplasmic organization of the rudiment. The main cytoplasmic elements which seem important in scale morphogenesis, on the basis of frequency, orientation and grouping, are 60-A fibrils and microtubules.The difficulties in understanding how regional differences in mature cells arise have been stressed by Waddington (23). In the development of an insect scale, there is a radical modification of cell size and shape resulting in an intricate surface pattern. One may ask if the development of the final pattern is foreshadowed in any way by the cytoplasmic organization of the cell in the earliest stages of the change.

Making photonic structures via cell culture: Morpho butterfly scales

“…On the wing, the scale cell is held by specialised socket cells within a general lamina of cells. 9,10 Cell lines would therefore possibly need to be derived from wing imaginal discs. However, published cell lines from imaginal discs still do not produce scales.…”

“…After the initiation of a scale, the cell would then need to secrete cuticle: scales finally result from the covering of precisely arrayed cell structures with chitin. 9,10 In general, it is clear that Morpho crysalises are not the ideal candidates for cell culture studies; they are far from model species. Most problematic, however, is the concept that each scale on the Morpho wing results from the sacrifice of a living cell: the scale cell.…”

“…Although Ghiradella 9 and Overton 10 have studied butterfly scale morphogenesis in general, this represents the first study on cell culture in the iconic Morpho species. As part of this study, the methodology required experimentation, and the final procedure used is itself an important part of the results.…”

A review of the diversity and evolution of photonic structures in butterflies, incorporating the work of John Huxley (The Natural History Museum, London from 1961 to 1990)

“…However, in this case, the reflectors are formed by multiple cells contributing to the same optical structure, and optical improvements probably arose due to incremental changes in the genome, which led directly to incremental changes in chitin deposition. In butterflies, however, developmental studies have shown that individual scales (optical devices) originate from single cells (Overton 1966).…”

“…We have been aware of structural colours for some time, Newton (1704) having surmised that they were responsible for the iridescence of male peacock tail feathers. Since then they have been found in a diverse range of taxa, including birds (Prum et al 1999;Zi et al 2003;Li et al 2005;Vigneron et al 2006), fishes (Denton & Nichol 1965, 1966, molluscs (Denton & Land 1971), annelids (Parker et al 2001), cnidarians (Welch et al , 2006 and arthropods (Parker 1995;Parker et al 1998Parker & Hegedus 2003;Vigneron et al 2005). Butterflies, however, reveal the most diverse range of reflectors in any taxon, probably because they possess scales that bear complex architectures at the sub-micron level-a very suitable platform for the evolution of structural colours.…”