Abstract
The reproductive development and maturation of female schistosomes are crucial since their released eggs are responsible for the host immunopathology and transmission of schistosomiasis. However, little is known about the nutrients required by female Schistosoma japonicum during its sexual maturation. We evaluated the promoting effect of several nutrients (calf serum, red blood cells (RBCs), ATP and hypoxanthine) on the reproductive development of pre-adult females at 18 days post infection (dpi) from mixed infections and at 50 dpi from unisexual infections of laboratory mice in basic medium RPMI-1640. We found RBCs, rather than other nutrients, promoted the female sexual maturation and egg production with significant morphological changes. In 27% of females (18 dpi) from mixed infections that paired with males in vitro on day 14, vitelline glands could be positively stained by Fast Blue B; and in 35% of females (50 dpi) from unisexual infections on day 21, mature vitelline cells were observed. Infertile eggs were detected among both groups. To analyze which component of mouse RBCs possesses the stimulating effect, RBCs were fractionated and included in media. However, the RBC fractions failed to stimulate development of the female reproductive organs. In addition, bovine hemoglobin hydrolysate, digested by neutral protease, was found to exhibit the promoting activity instead of untreated bovine hemoglobin. The other protein hydrolysate, lactalbumin hydrolysate, exhibited a similar effect with bovine hemoglobin hydrolysate. Using quantitative RT-PCR, we found the expression levels of four reproduction-related genes were significantly stimulated by RBCs. These data indicate that RBCs provide essential nutrients for the sexual maturation of female S. japonicum and that the protein component of RBCs appeared to constitute the key nutrient. These findings would improve laboratory culture of pre-adult schistosomes to adult worms in medium with well-defined components, which is important to investigate the function of genes related to female sexual maturation.
Highlights
Schistosomiasis is a worldwide distributed disease infecting over 200 million people and threatening nearly 800 million [1]
These findings indicate that erythrocytes are a prerequisite for the sexual maturation of the female of S. japonicum besides being in copula with males, for it provided essential nutrients for reproductive development and that the protein component was the key nutrient
Medium supplemented with Red blood cells (RBCs) supported reproductive development of pre-adult female S. japonicum
Summary
Schistosomiasis is a worldwide distributed disease infecting over 200 million people and threatening nearly 800 million [1]. Once the worm pairs are in copula, the gonads of the female develop to maturation for egg production [5,6,7]. The maturation of vitellaria and ovaries fails to commence in virgin female schistosomes [8, 9]. The mechanism of this male-dependent female sexual maturation remains to be fully elucidated the phenomenon is the focus of substantial interest [10]. In addition to continuous pairing with the male, the maturation of female schistosomes requires a considerable quantity of nutrients, from ingested blood, to support maturation and the release of several thousand eggs daily from each female S. japonicum for many months or years [11]. The knowledge of the essential nutritional demand for the reproductive development in schistosomes is of importance to optimize culture conditions that, in turn, can be expected benefit to the in vitro studies of the male-female interplay
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