Abstract
BackgroundVitellogenin (Vg), a key molecule for oocyte development synthesized in the fat body during blood-feeding, is released into the hemolymph and then taken into the oocytes via Vg receptor (VgR) in ticks. Previously, we showed that VgR mRNA is expressed in the ovary at the adult stage of parthenogenetic Haemaphysalis longicornis ticks and its expression increases after blood-feeding. However, intracellular localization of VgR mRNA and protein at each developmental stage of oocytes during oogenesis remains largely unclear.MethodsmRNA and protein expression profiles of H. longicornis VgR (HlVgR) in the oocytes from the unfed to oviposition periods were analyzed by real-time PCR, in situ hybridization, and immunostaining. To elucidate the timing of the onset of Vg uptake, RNA interference (RNAi)-mediated gene silencing of HlVgR was performed.ResultsIn situ hybridization revealed that HlVgR mRNA was detected in the cytoplasm of stage I-III oocytes, and weaker positive signals for HlVgR mRNA were found in the cell periphery of stage IV and V oocytes. Likewise, HlVgR protein was detected by immunostaining in the cytoplasm of stage I-III oocytes and in the cell periphery of stage IV and V oocytes. Each developmental stage of the oocytes showed distinct patterns of mRNA and protein expression of HlVgR. Moreover, RNAi of HlVgR caused delayed or arrested development in the oocytes. The ovaries of control ticks showed all developmental stages of oocytes, whereas stage I-III oocytes were found in the ovaries of HlVgR-RNAi ticks at 5 days after engorgement.ConclusionsThese results suggest that active uptake of Vg is required for development from stage III to stage IV during oogenesis. Our data clearly revealed an apparent shift in the intracellular localization of VgR for both mRNA and protein level in oocytes during oogenesis.
Highlights
Vitellogenin (Vg), a key molecule for oocyte development synthesized in the fat body during bloodfeeding, is released into the hemolymph and taken into the oocytes via Vg receptor (VgR) in ticks
The expression levels of H. longicornis VgR (HlVgR) in the rapid feeding period were higher than those at previous periods (t(5) = − 8.798, P = 0.0003) and were the highest at engorgement (t(5) = − 13.761, P < 0.0001). These results suggest that HlVgR was upregulated in the ovary during blood-feeding
Our study revealed that an apparent shift in the intracellular localization of HlVgR mRNA and protein was associated with the developmental stages of oocytes in parthenogenetic H. longicornis ticks
Summary
Vitellogenin (Vg), a key molecule for oocyte development synthesized in the fat body during bloodfeeding, is released into the hemolymph and taken into the oocytes via Vg receptor (VgR) in ticks. Nutrients derived from a blood meal allow the synthesis of vitellogenin (Vg), an essential molecule for oocyte development, in the fat body of female ticks, being stimulated by ecdysteroid hormones [1,2,3,4,5,6,7,8,9,10]. Subsequent studies revealed that vitellogenesis is controlled by the activation of the target of rapamycin (TOR), a key molecule of a nutrient-sensing pathway in eukaryotic cells, through ecdysteroid hormone stimulation [12]. TOR phosphorylates S6 kinase and regulates the transcription and intracellular localization of a GATA factor in the fat body. Our previous data suggested that the serine/threonine protein kinase Akt is an upstream factor of TOR and essential for controlling gene transcription and for regulating vitellogenesis [13]
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