Abstract
Vitellogenesis-inhibiting hormone (VIH) negatively regulates reproduction in shrimp and other decapod crustaceans. In order to assess the effects of transcriptional silencing by multiple VIH subtype I sinus gland peptides (SGPs) on ovarian maturation in female whiteleg shrimp, Litopenaeus vannamei, we synthesized five dsRNAs targeting Liv-SGP-A, −B, −C, −F, and −G and injected them into subadults. The following treatments were employed: sgpG-dsRNA (targeting Liv-SGP-G), sgpC-dsRNA (targeting Liv-SGP-C), and mixed-dsRNA (targeting Liv-SGP-A, −B, and −F). The expression of Liv-SGP-G in eyestalks was significantly decreased at 10, 20, and 30 days after the injection of sgpG-dsRNA In addition, it was significantly decreased at 10 and 30 days after the injection of mixed-dsRNA. The expression of vitellogenin (Vg) gene expression in the ovaries, and concentrations of Vg protein in the hemolymph, were not changed by the administration of any dsRNA treatment (the ovaries remained immature in all treated individuals and contained mostly oogonia and previtellogenic oocytes). Although the administration of dsRNAs corresponding to multiple VIHs did not promote ovarian maturation, this is the first report of the co-transcriptional repression of Liv-SGP-G by the injection of dsRNA for homologous genes (Liv-SGP-A, −B, and −F). These results indicate that subadults can respond to the techniques of transcriptional silencing.
Highlights
The hormonal regulation of ovarian maturation in decapod Crustacea is more well-understood in relation to inhibitory factors than to stimulatory factors
The use of RNA interference (RNAi) to silence hormonal transcripts of factors that negatively regulate reproduction offers an opportunity to develop alternatives to eyestalk ablation in shrimp. This is because it is generally known that vitellogenesis-inhibiting hormone (VIH) is produced in the eyestalks and the removal of the source of VIH by eyestalk ablation allows ovarian maturation to occur
In previous work of this laboratory, several sinus gland peptides (SGP) were purified from the eyestalks of subadult Litopenaeus vannamei, and six of these were shown to inhibit vitellogenin (VG) gene expression levels using of Marsupenaeus japonicus ovary as the in vitro incubation system [7]
Summary
The hormonal regulation of ovarian maturation in decapod Crustacea is more well-understood in relation to inhibitory factors than to stimulatory factors. Eyestalk ablation is frequently employed as an artificial means of promoting ovarian maturation in economically important shrimp species, and is frequently used in commercial hatcheries to induce spawning [1,2,3]. For this reason, it had long been assumed that the eyestalk harbors a maturation-inhibiting factor, referred to as vitellogenesis-inhibiting hormone (VIH; gonad-inhibiting hormone, GIH). In Litopenaeus vannamei and other penaeid shrimp species, VIH comprises a set of peptide hormones that belong to the crustacean hyperglycemic hormone (CHH) family. CHH is of subtype I, and VIH, MIH, and MOIH are of subtype II; subtype I VIH has been reported in the penaeid shrimps Penaeus japonicus and L. vannamei [4,5,6,7]
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