Ultrabithorax is amicromanager of hindwing identity in butterflies and moths

Authors: TENDOLKAR, AMRUTA - George Washington University; POMERANTZ, AARON - University Of California; HERYANTO, CHRISTA - George Washington University; SHIRK, PAUL - Retired ARS Employee; PATEL, NIPAM - University Of California; MARTIN, ARNAUD - George Washington University

Submitted to: Frontiers in Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2021
Publication Date: 3/18/2021
Citation: Tendolkar, A., Pomerantz, A.F., Heryanto, C., Shirk, P.D., Patel, N.H., Martin, A. 2021. Ultrabithorax is amicromanager of hindwing identity in butterflies and moths. Frontiers in Ecology and Evolution. Article 9:643661. https://doi.org/10.3389/fevo.2021.643661.
DOI: https://doi.org/10.3389/fevo.2021.643661

Interpretive Summary: During development, structural features, spot patterns and coloration of insect wings is managed by homeotic genes that provide the overall control of the outcome. 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. Ultrabithorax (Ubx) is proposed as a master selector gene that differentiate metathoracic from mesothoracic identities. Scientists at George Washington University, University of California Berkeley in collaboration with those at USDA ARS, Center for Medical, Agricultural, and Medical Entomology, Gainesville, Florida, examined the functions of Ultrabithorax using CRISPR/Cas9 gene editing to produce somatic mutations to modify the pattern formation outcome in butterflies and moths. The CRISPR genetic knockouts of Ultrabithorax resulted in variable scale morphologies, color patterns and wing venation and structure. The results show that Ultrabithorax is a master selector of lepidopteran hindwing identity and suggest it acts on many gene regulatory networks involved in wing development and patterning. Understanding these developmental cues facilitates understanding structural and pattern formation not only in insects but all higher eukaryotes.

Technical 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 hindwingspecific 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 wingcoupling 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.