Biology subjects

Seah, K. S.

Publications and source records attributed to Seah, K. S..

3 recordsLinked to original sources

bioRxiv2021

Conserved roles of Distal-less and spalt in regulating butterfly melanic patterns

Two genes, Distal-less (Dll) and spalt (sal), are known to be involved in establishing nymphalid butterfly wing patterns. They function in several ways: in the differentiation of the eyespots central signaling cells, or foci; in the differentiation of the surrounding black disc; in overall scale melanisation (Dll); and in elaborating marginal patterns, such as parafocal elements. However, little is known about the functions of these genes in the development of wing patterns in other butterfly families. Here, we study the expression and function of Dll and sal in the development of spots and other melanic wing patterns of the Indian cabbage white, Pieris canidia, a pierid butterfly. In P. canidia, both Dll and Sal proteins are expressed in the scale-building cells at the wing tips, in chevron patterns along the pupal wing margins, and in areas of future scale melanisation. Additionally, Sal alone is expressed in the future black spots. CRISPR knockouts of Dll and sal showed that each gene is required for the development of melanic wing pattern elements, and repressing pteridine granule formation, in the areas where they are expressed. We conclude that both genes likely play ancestral roles in organising distal butterfly wing patterns, across pierid and nymphalid butterflies, but are unlikely to be differentiating signalling centers in pierids black spots. The genetic and developmental mechanisms that set up the location of spots and eyespots are likely distinct in each lineage.

evolutionary biology↗

bioRxiv2021

optix is involved in eyespot development via a possible positional information mechanism

Novel organismal traits might reuse ancestral gene-regulatory networks (GRNs) in their development, but data supporting this mechanism are still sparse. Here we show the reuse of an ancestral insect venation gene regulatory subnetwork patterning the sharp and distinct rings of color in butterfly eyespots. Using laser microdissection followed by RNA-Seq we first obtained transcriptional profiles of the anterior and posterior compartment of larval wings, and eyespot and adjacent control tissue in pupal wings of Bicyclus anynana butterflies. We identified key venation patterning genes such as Mothers against dpp 6 (Mad6), thickveins, Optix, spalt, optomotor-blind (omb), aristaless, cubitus interruptus, and patched differentially expressed (DE) across compartments, and a sub-set of these genes also DE across eyespot and non-eyespot samples. Fluorescent in-situ hybridization (HCR3.0) on the jointly DE genes Mad6, Optix, and spalt, as well as dpp showed clear eyespot-center, eyespot-rings, and compartment-specific expression. Knocking out dpp resulted in an individual with venation defects and loss of eyespots, whereas knockouts of Optix and spalt resulted in the loss of orange scales and black scales, respectively. Furthermore, using CRISPR-Cas9 followed by immunostainings, we showed that Spalt represses Optix in the central region of the eyespot, limiting Optix expression to a more peripheral ring, which parallels the regulatory interaction found in venation patterning in the anterior compartment of fly larval wings. These network similarities suggest that part of the venation GRN was co-opted to aid in the differentiation of the eyespot rings. One-sentence summaryWe showed the reuse of an ancestral insect wing venation GRN in patterning a novel complex trait in butterflies.

developmental biology↗

bioRxiv2020

F-actin Re-organization Mediates Hierarchical Morphogenesis of Swallowtail Butterfly Wing Scale Nanostructures

The study of color patterns in the animal integument is a fundamental question in biology, with many lepidopteran species being exemplary models in this endeavor due to their relative simplicity and elegance. While significant advances have been made in unravelling the cellular and molecular basis of lepidopteran pigmentary coloration, the morphogenesis of wing scale nanostructures involved in structural color production is not well understood. Contemporary research in this topic largely focuses on a few nymphalid model taxa (e.g., Bicyclus, Heliconius), despite an overwhelming diversity in the hierarchical nanostructural organization of lepidopteran wing scales. Here, we present a time-resolved, comparative developmental study of hierarchical scale nanostructures in Parides eurimedes and five other papilionid species. Our results uphold the putative conserved role of F-actin bundles in acting as spacers between developing ridges, as previously documented in several nymphalid species. Interestingly, while ridges are developing in P. eurimedes, plasma membrane manifests irregular mesh-like crossribs characteristic of Papilionidae, which delineate the accretion of cuticle into rows of planar disks in between ridges. Once the ridges have grown, disintegrating F-actin bundles appear to reorganize into a network that supports the invagination of plasma membrane underlying the disks, subsequently forming an extruded honeycomb lattice. Our results uncover a previously undocumented role for F-actin in the morphogenesis of complex wing scale nanostructures, likely specific to Papilionidae.

developmental biology↗