A critical role for ecdysone response genes in regulating egg production in adult female Rhodnius prolixus

Abstract

Ecdysteroids control ovary growth and egg production through a complex gene hierarchy. In the female Rhodnius prolixus, a blood-gorging triatomine and the vector of Chagas disease, we have identified the ecdysone response genes in the ovary using transcriptomic data. We then quantified the expression of the ecdysone response gene transcripts (E75, E74, BR-C, HR3, HR4, and FTZ-F1) in several tissues, including the ovary, following a blood meal. These results confirm the presence of these transcripts in several tissues in R. prolixus and show that the ecdysone response genes in the ovary are mostly upregulated during the first three days post blood meal (PBM). Knockdown of E75, E74, or FTZ-F1 transcripts using RNA interference (RNAi) was used to understand the role of the ecdysone response genes in vitellogenesis and egg production. Knockdown significantly decreases the expression of the transcripts for the ecdysone receptor and Halloween genes in the fat body and the ovaries and reduces the titer of ecdysteroid in the hemolymph. Knockdown of each of these transcription factors typically alters the expression of the other transcription factors. Knockdown also significantly decreases the expression of vitellogenin transcripts, Vg1 and Vg2, in the fat body and ovaries and reduces the number of eggs produced and laid. Some of the laid eggs have an irregular shape and smaller volume, and their hatching rate is decreased. Knockdown also influences the expression of the chorion gene transcripts Rp30 and Rp45. The overall effect of knockdown is a decrease in number of eggs produced and a severe reduction in number of eggs laid and their hatching rate. Clearly, ecdysteroids and ecdysone response genes play a significant role in reproduction in R. prolixus.

RNA Interference-Mediated Suppression of Ecdysone Signaling Inhibits Choriogenesis in Two Coleoptera Species

“…Thirdly, knockdown of either EcR or usp significantly repressed oviposition in both H. vigintioctopunctata (Figures 2 and 3) and L. decemlineata (Figure 5) females. In accordance with our data, knockdown of EcR, usp, E75, E74 or FTZ-F1 decreases mature eggs, and severely reduces the laid eggs and their hatching rate in R. prolixus [23,24]. The reduced oviposition in 20E signal repressed females has also been documented in T. castaneum [7], D. melanogaster [25], Nilaparvata lugens [26,27], and Cimex lectularius [28].…”

“…Secondly, our data showed that the EcR and usp transcripts were present in the ovaries in both H. vigintioctopunctata (Figures 1-3) and L. decemlineata (Figures 1 and 5) females, similar to those in R. prolixus [23,24].…”

“…Lastly, we discovered that RNAi of either EcR or usp destroyed the structure of eggshells and deformed oocyte shapes (Figures 2, 3 and 5). Consistently, some of the eggs have an irregular shape and smaller volume laid by the EcR, usp, E75, E74 or FTZ-F1 RNAi R. prolixus females [23,24]. The deformation of chorion structure and oocyte shape gives a solid piece of experimental evidence that 20E cascade triggers choriogenesis, in addition to activating vitellogenesis in both H. vigintioctopunctata and L. decemlineata females [21].…”

“…As a result, oocytes are continuously matured and the oviposition persists in mature H. vigintioctopunctata females [20]. Likewise, ecdysone response gene transcripts (E75, E74, BrC, HR3, HR4, and FTZ-F1) are mostly upregulated in the ovary during the first three days post blood meal in Rhodnius prolixus [23].…”