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Genetic interactions between E93, Krüppel homolog-1 and Broad-Complex transcription factors underlie the formation of the holometabolous pupa

AuthorsUreña, Enric ; Franch-Marro, Xavier ; Martín Casacuberta, David A.
Issue DateJul-2015
Citation2nd International Insect Hormone Workshop (2015)
AbstractComplete metamorphosis (Holometaboly) is a key innovation that underlies the spectacular success of holometabolous insects. Holometabola form a monophyletic group that evolved from ancestors that exhibit hemimetabolous development (Hemimetaboly). Unfortunately, the molecular mechanisms underlying this crucial transition, including the occurrence of the holometabolan-specific pupal stage, are poorly understood. Despite the differences, the genetic switch between juvenile and adult programs in both types of insects relies on the disappearance of juvenile hormone (JH), which prevents metamorphosis until the final juvenile stage through the induction of the anti-metamorphic krüppel-homolog 1 (Kr-h1) transcription factor. A second important metamorphic gene is Broad-complex (Br-C), although its role, in contrast to Kr-h1, is specific of holometabolus insects in the formation of the pupal form. In addition to these two genes, our group has recently identified E93 as the critical transcription factor that promotes adult metamorphosis in both hemimetabolous and holometabolous insects, thus acting as the conserved adult specifier in all winged insects. Using gene silencing by RNAi in the German cockroach Blattella germanica, the red flour beetle Tribolium castaneum and the fruit fly Drosophila melanogaster, we show that depletion of E93 prevents adult metamorphosis and induces endless repetitions of nymphal molts in hemimetabolous insects and the repetition of the pupal program in holometabolous insects. In addition to promoting adult differentiation, we show that E93 is also required to repress the expression of Kr-h1 and Br-C during the last immature stages of hemimetabolous and holometabolous insects ensuring the accurate transition to the adult forms. Finally, we demonstrate that critical changes in the expression and in the regulatory interactions between E93, Kr-h1 and Br-C factors during the final larval stage of holometabolous insects have played a critical role in facilitating the formation of the pupal stage. In particular, we show that the transient pulse of Kr-h1 at the end of the larval development prevents the direct transformation of larval tissues to adult ones by maintaining low levels of E93 during this period and, in doing so, allowing the strong up-regulation of TcBr-C and the occurrence of a new developmental stage, the pupa.
DescriptionTrabajo presentado en el 2nd International Insect Hormone Workshop, celebrado en Creta del 12 al 18 de julio de 2015.
Appears in Collections:(IBE) Comunicaciones congresos
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