title: Homeotic evidence for the appendicular origin of the labrum in Tribolium castaneum.
abstract: The ontogeny of the insect labrum, or upper lip, has been debated for nearly a century. Recent molecular data suggest a segmental appendage origin of this structure. Here we report the first arthropod mutation associated with a homeotic transformation of the labrum. Antennagalea-5 (Ag(5)) transforms both antennal and labral structures to resemble those of gnathal appendages in Tribolium castaneum. This labral transformation suggests that the labrum is a fused structure composed of two pairs of appendage endites, and is serially homologous to the gnathal appendages.
authors.affiliation: USDA, ARS, Grain Marketing and Production Research Center, Manhattan, KS 66502, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Haas
authors.forename: S J
authors.initials: SJ
authors.lastname: Brown
authors.forename: R W
authors.initials: RW
authors.lastname: Beeman
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D005121:Extremities / Q000033:anatomy & histology / Q000196:embryology; D005801:Genes, Homeobox / Q000235:genetics / Q000502:physiology*; D017344:Genes, Insect / Q000235:genetics / Q000502:physiology*; D006257:Head / Q000033:anatomy & histology* / Q000196:embryology*; D009055:Mouth / Q000033:anatomy & histology / Q000196:embryology / Q000378:metabolism; D009154:Mutation / Q000235:genetics / Q000528:radiation effects; D014231:Tribolium / Q000033:anatomy & histology* / Q000196:embryology* / Q000235:genetics / Q000528:radiation effects