The functional evolution of collembolan Ubx on the regulation of abdominal appendage formation

Abstract

AbstractFolsomia candidais a tiny soil-living arthropod belonging to the Collembola, which represents one of the basal hexapods and serves as an outgroup lineage to Insecta. It possesses three abdominal appendages: the ventral tube located in the first abdominal segment (A1), the retinaculum in A3 and the furca in A4, which are morphologically distinctive to the thorax limbs. Collembolan Ubx and AbdA are responsible for specifying their abdominal appendages; however, they are unable to repress the expression of the appendage marker geneDll. To date, the genes involved in appendage formation during collembolan embryogenesis and the mechanisms by which Ubx and AbdA regulateDlltranscription and subsequently regulate appendage development remain unknown. In this study, we analysed the developmental transcriptomes ofF. candidaand identified 36 candidate genes that may be involved in appendage formation, includingUbx(FcUbx). Furthermore, via electrophoretic mobility shift assays and dual luciferase assays, we found that the binding and repression capacity of FcUbx onDrosophila Dllresembles those of the longest isoform ofDrosophilaUbx (DmUbx_Ib), while the regulatory mechanism of the C-terminus of FcUbx onDllrepression is similar to that of crustaceanArtemia franciscanaUbx (AfUbx), demonstrating that the function of collembolan Ubx is intermediate between that of Insecta and Crustacea. Overall, our study provides novel insights into appendage formation and reconstruction of the functional evolutionary trajectory of Ubx on abdominal appendages from crustaceans to insects.