RXR/USP and EcR are critical for the regulation of reproduction and the control of JH biosynthesis in Diploptera punctata

Hult EF, Huang J, Marchal E, Lam J, Tobe SS

J. Insect Physiol. 2015 Sep;80:48-60

PMID: 25917982

Abstract

During development and reproduction the response to ecdysteroids is mediated by a heterodimeric receptor complex comprising the retinoid X receptor/ultraspiracle (RXR/USP) and the ecdysone receptor (EcR). Here, the role of these receptors in the endocrine control of reproduction is examined in the cockroach Diploptera punctata. We report the sequence of four DpRXR and three DpEcR splice variants, including the first description of a Drosophila EcRB2-like isoform in a hemimetabolous insect. DpRXR and DpEcR are broadly expressed in the tissues of adult females, with relatively high transcript levels in the corpora allata (CA), nervous tissue and ovary. Developmental profiling revealed an inverse correlation between DpRXR and DpEcR expression and the activity of the CA. RNAi-mediated depletion of DpRXR and DpEcR did not affect oocyte growth, but inhibited oviposition and impaired chorion formation. Retained oocytes exhibited a degenerating follicular epithelium and were slowly resorbed. Treated animals showed significantly higher rates of JH biosynthesis and a decrease in ecdysteroid titers at the end of vitellogenesis. Reduction of DpRXR and DpEcR expression resulted in an upregulation of genes involved in JH production and a downregulation of allatostatin receptor mRNA in the CA. Treatment with dsRNA also affected the expression of genes downstream of JH in target tissues including vitellogenin and Kr├╝ppel-homolog 1 as well as Broad-Complex, an early ecdysone response gene. Overall, results suggest that DpRXR and DpEcR are not required early in the reproductive cycle when events are JH-dependent, but do mediate critical ecdysteroid feedback to the CA late in the gonadotropic cycle.