NR5A nuclear receptors coordinately regulate locust metamorphic transition and fecundity

NR5A nuclear receptors Ftz-f1 and HR39 are evolutionarily conserved with essential roles in insect development and reproduction, yet their divergent and isoform-specific functions in metamorphosis and reproduction remain unclear. Besides a single HR39 transcript, two Ftz-f1 transcript variants are identified in diverse insect species including Locusta migratoria. The locust paralogues exhibit spatiotemporal fluctuations in mRNA levels, with LmαFtz-f1 and LmHR39 transcripts being more abundant than LmβFtz-f1, and at higher levels in adults than nymphs. Both LmFtz-f1 and LmHR39 are required for metamorphosis and reproduction. Compared to LmHR39 RNAi, simultaneous knockdown of LmαFtz-f1 and LmβFtz-f1 led to severer defects in nymph-to-adult transition, vitellogenin (Vg) synthesis, and egg development. Loss of LmαFtz-f1 function caused mild defective phenotypes of metamorphosis, but remarkably reduced Vg transcription along with arrested ovarian development and blocked egg development, whereas LmβFtz-f1 silencing mainly disrupted metamorphosis with little effect on vitellogenesis. Transcriptome analysis showed that knockdown of LmFtz-f1 or LmHR39 in nymphs altered ecdysone and juvenile hormone pathway genes, while in adults they affected cell cycle and translation, respectively. These results indicate that LmFtz-f1 is the dominant NR5A, with LmαFtz-f1 pivotal in reproduction and LmβFtz-f1 specialized in metamorphosis, highlighting the coordinated regulation of NR5A in insect key life-history traits.