TGF ß/activin-dependent activation of Torso controls the timing of the metamorphic transition in the red flour beetle < i > Tribolium castaneum < /i >

In this study, we investigate the role of the interaction between the Torso and TGF ß/activin signaling pathways in regulating metamorphic timing in the red flour beetle,Tribolium castaneum. Our results show that Torso signaling is required specifically during the last larval instar and that its activation is mediated not only by the prothoracicotropic hormone (Tc-Ptth) but also by Trunk (Tc-Trk), another ligand of the Tc-Torso receptor. Interestingly, we show that while Torso activation by Tc-Ptth determines the onset of metamorphosis, Tc-Trk promotes growth during the last larval stage. In addition, we found that the expression ofTc-torso correlates with the attainment of the TS and the decay of juvenile hormone (JH) levels, at the onset of the last larval instar. Notably, our data reveal that activation of TGF ß/activin signaling pathway at the TS is responsible for repressing the JH synthesis and inducingTc-torso expression, initiating metamorphosis. Altogether, these findings shed light on the pivotal involvement of the Ptth/Trunk/Torso and TGF ß/activin signaling pathways as critical regulatory components orchestrating the TS-driven metamorphic initiation, offering valuable insights into the mechanisms underlying body size determination in insects.
Source: PLoS Genetics - Category: Genetics & Stem Cells Authors: Source Type: research