Ultrabithorax Is a Micromanager of Hindwing Identity in Butterflies and Moths

Abstract

The forewings and hindwings of butterflies and moths (Lepidoptera) are differentiated from each other, with segment-specific morphologies and color patterns that mediate a wide range of functions in flight, signaling, and protection. The Hox gene Ultrabithorax (Ubx) is a master selector gene that differentiates metathoracic from mesothoracic identities across winged insects, and previous work has shown this role extends to at least some of the color patterns from the butterfly hindwing. Here we used CRISPR targeted mutagenesis to generate Ubx loss-of-function somatic mutations in two nymphalid butterflies (Junonia coenia, Vanessa cardui) and a pyralid moth (Plodia interpunctella). The resulting mosaic clones yielded hindwing-to-forewing transformations, showing Ubx is necessary for specifying many aspects of hindwing-specific identities, including scale morphologies, color patterns, and wing venation and structure. These homeotic phenotypes showed cell-autonomous, sharp transitions between mutant and non-mutant scales, except for clones that encroached into the border ocelli (eyespots) and resulted in composite and non-autonomous effects on eyespot ring determination. In the pyralid moth, homeotic clones converted the folding and depigmented hindwing into rigid and pigmented composites, affected the wing-coupling frenulum, and induced ectopic scent-scales in male androconia. These data confirm Ubx is a master selector of lepidopteran hindwing identity and suggest it acts on many gene regulatory networks involved in wing development and patterning.

Antennapedia and optix regulate metallic silver wing scale development and cell shape in Bicyclus anynana butterflies

“…Among the genes investigated, apA and Ubx are well known homeotic genes that specify wing-surface or wing-specific identities in butterflies, respectively (Matsuoka and Monteiro, 2021;Prakash and Monteiro, 2018;Tendolkar et al, 2021;Weatherbee et al, 1999). In B. anynana, apA expression is restricted to dorsal wing surfaces and Ubx is restricted to hindwings, and both genes have homogeneous expression across those wings/surfaces (Matsuoka and Monteiro, 2021;Prakash and Monteiro, 2018).…”

Butterfly wings exhibit spatial variation in chromatin accessibility

“…The discovery that many OCRs were unique to either forewings or hindwings may be explained by upstream regulators involved in differentiating the identity of these wings. The Hox gene Ultrabithorax (Ubx) is expressed only in hindwing tissue and knocking this gene out transforms hindwings to forewing identity in butterflies and moths (Matsuoka and Monteiro 2019;Tendolkar et al 2021). Thus, Ubx could be involved in regulating the open chromatin profile that is unique to the hindwings.…”

“…The copyright holder for this preprint this version posted January 22, 2022. ; https://doi.org/10.1101/2022.01.21.477190 doi: bioRxiv preprint hindwings to forewing identity in butterflies and moths (Matsuoka and Monteiro 2019;Tendolkar et al 2021). Thus, Ubx could be involved in regulating the open chromatin profile that is unique to the hindwings.…”

Body Plan Identity: A Mechanistic Model

“…At higher levels of morphology, an especially clear example concerns the insect homeobox gene Ultrabithorax (Ubx). Knockdown of Ubx in Tribolium results in development of forewing identity (elytra) in the position of the hindwing, indicating that the gene functions as a simple modular switch for a complex cascade of developmental processes of wing morphogenesis (Deutsch 2005;Wagner 2007Wagner , 2014Tendolkar et al, 2021). In this sense, Ubx controls hindwing character identity, as opposed to the phenotypic state of the wing (e.g.…”