Abstract
BackgroundThe tick Haemaphysalis longicornis exhibits two separate reproductive populations: bisexual and parthenogenetic, which have diploid and triploid karyotypes, respectively. The parthenogenetic population can undergo engorgement without copulation and produce viable female-only offspring with a longer incubation period than the bisexual population. Three enzymes, cathepsin B, cathepsin D and acid phosphatase, were found to be involved in vitellin degradation during the embryonic development of bisexual H. longicornis. However, the expression and activity profiles of these enzymes during the embryonic development of parthenogenetic ticks remain unknown. In the present study, the transcriptional expression profile, enzyme activity and roles in embryogenesis of the three enzymes during the embryonic development of parthenogenetic H. longicornis were investigated.MethodsQuantitative real-time polymerase chain reaction (qPCR) and fluorescence detection were used to analyze the dynamic changes in the three enzymes during embryogenesis. The roles of the three enzymes during embryogenesis were also explored using RNA interference (RNAi).ResultsThe three enzymes were all expressed during embryonic development in parthenogenetic H. longicornis. The expression of cathepsin B was highest on day 15, whereas that of cathepsin D was highest on day 3 and the peak of acid phosphatase expression occurred on day 9. The activity of cathepsin B was highest on day 3 and lowest on day 5, then gradually increased and remained stable. Cathepsin D activity was highest on day 1 and showed a gradually decreasing trend, whereas acid phosphatase showed the opposite trend and reached a peak on day 23. RNA interference experiments in engorged female ticks revealed that there was no significant difference in the number of eggs laid, but the hatching rate of the eggs was significantly decreased.ConclusionThe three enzymes all play important roles in embryonic development of H. longicornis, but the expression patterns and changes in the activity of the enzymes in the bisexual and parthenogenetic populations are different. The results will help a better understanding of the similarities and differences underlying embryonic development in the bisexual and parthenogenetic populations and contribute to the future exploration of the development of the parthenogenetic population of H. longicornis.
Highlights
The tick Haemaphysalis longicornis exhibits two separate reproductive populations: bisexual and par‐ thenogenetic, which have diploid and triploid karyotypes, respectively
Cloning of the cathepsin B, cathepsin D and acid phosphatase genes for Quantitative real-time polymerase chain reaction (qPCR) Total RNA was extracted from eggs collected at 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21 and 23 days and converted
Expression and activity of cathepsin B during embryogenesis To illustrate the functions of cathepsin B during embryogenesis, the transcriptional expression profile of cathepsin B was monitored via qPCR
Summary
The tick Haemaphysalis longicornis exhibits two separate reproductive populations: bisexual and par‐ thenogenetic, which have diploid and triploid karyotypes, respectively. Haemaphysalis longicornis is a three-host tick that is widely distributed in Australia, New Zealand, Korea, Japan and China [8] It was found in Hunterdon County, New Jersey, USA for the first time [9]. It is an essential vector of zoonotic agents and can transmit severe fever with thrombocytopenia syndrome virus and Anaplasma, Babesia, Borrelia, Ehrlichia and Rickettsia bacteria [10]. Parthenogenetic H. longicornis can complete their life-cycle without fertilization, without any males being observed throughout the life-cycle and they show strict reproductive isolation from the bisexual population [11, 12]. The egg weight of the parthenogenetic population is greater than that of the bisexual population, the hatching rate is lower [11, 12]
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