Limitation of food availability (starvation) is known to influence the reproductive ability of animals. Autophagy is a lysosomal driven degradation process that protects the cell under metabolic stress conditions, such as during nutrient shortage. Whether, and how starvation-induced autophagy impacts on the maturation and function of reproductive organs in animals are still open questions. In this study, we have investigated the effects of starvation on histological and cellular changes that may be associated with autophagy in the ovary of the giant freshwater prawn, Macrobachium rosenbergii. To this end, the female prawns were daily fed (controls) or unfed (starvation condition) for up to 12 days, and the ovary tissue was analyzed at different time-points. Starvation triggered ovarian maturation, and concomitantly increased the expression of autophagy markers in vitellogenic oocytes. The immunoreactivities for autophagy markers, including Beclin1, LC3-II, and Lamp1, were enhanced in the late oocytes within the mature ovaries, especially at the vitellogenic stages. These markers co-localized with vitellin in the yolk granules within the oocytes, suggesting that autophagy induced by starvation could drive vitellin utilization, thus promoting ovarian maturation.
The giant freshwater prawn, Macrobrachium rosenbergii, is an economically valuable species that are distributed throughout the Asia-Pacific region. With the natural population declining due to overfishing, aquaculture of this species is deemed necessary. Hence, it is essential to understand the mechanisms regulating reproduction in order to increase their production. Prostaglandins (PGs) play an important role in reproduction in most vertebrates and several invertebrates. It has been proposed that crustaceans have PGs but the prostanoids pathway in the giant freshwater prawn is still unclear. In this study, we identified 25 prostanoid-related genes involved in the biosynthesis of active prostanoids in M. rosenbergii using in silico searches of transcriptome data. Comparative analysis of encoded proteins for the MroPGES2 gene with other species was performed to confirm their evolutionary conservation. Gene expression analysis revealed the correlation of MroPGES2 gene expression level with the progress of ovarian development. Eyestalk ablation increased the expression level of MroPGES2 gene compared to intact groups during the ovary maturation stages. Collectively, this study confirmed the existence of prostanoids in the giant freshwater prawn, as well as characterizing key gene MroPGES2 associated with the prostanoid pathway. We propose that MroPGES2 may play an important role in M. rosenbergii ovarian maturation and its expression is under the inhibitory control from the eyestalk optic ganglion hormones. Identification of genes in prostanoid pathway and their expressions enables future functional studies to be performed, which may lead to applications in the aquaculture of this species.
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