Characterization of nit sheath protein functions and transglutaminase-mediated cross-linking in the human head louse, Pediculus humanus capitis

Ju Hyeon Kim,Si Hyeock Lee,Do Eun Lee,Sangyoun Park,John M Clark

doi:10.1186/s13071-021-04914-z

Ju Hyeon Kim, Si Hyeock Lee + Show 3 more

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https://doi.org/10.1186/s13071-021-04914-z

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Abstract

BackgroundHead louse females secrete liquid glue during oviposition, which is solidified to form the nit sheath over the egg. Recently, two homologous proteins, named louse nit sheath protein (LNSP) 1 and LNSP 2, were identified as adhesive proteins but the precise mechanism of nit sheath solidification is unknown.MethodsWe determined the temporal transcriptome profiles of the head louse accessory glands plus oviduct, from which putative major structural proteins and those with functional importance were deduced. A series of RNA interference (RNAi) experiments and treatment of an inhibitor were conducted to elucidate the function and action mechanism of each component.ResultsBy transcriptome profiling of genes expressed in the louse accessory glands plus uterus, the LNSP1 and LNSP2 along with two hypothetical proteins were confirmed to be the major structural proteins. In addition, several proteins with functional importance, including transglutaminase (TG), defensin 1 and defensin 2, were identified. When LNSP1 was knocked down via RNA interference, most eggs became nonviable via desiccation, suggesting its role in desiccation resistance. Knockdown of LNSP2, however, resulted in oviposition failure, which suggests that LNSP2 may serve as the basic platform to form the nit sheath and may have an additional function of lubrication. Knockdown of TG also impaired egg hatching, demonstrating its role in the cross-linking of nit sheath proteins. The role of TG in cross-linking was further confirmed by injecting or hair coating of GGsTop, a TG inhibitor.ConclusionsBoth LNSP1 and LNSP2 are essential for maintaining egg viability besides their function as glue. The TG-mediated cross-linking plays critical roles in water preservation that are essential for ensuring normal embryogenesis. TG-mediated cross-linking mechanism can be employed as a therapeutic target to control human louse eggs, and any topically applied TG inhibitors can be exploited as potential ovicidal agents.Graphical abstract

Highlights

Head louse females secrete liquid glue during oviposition, which is solidified to form the nit sheath over the egg
Roles of LNSP1 and LNSP2 Knockdown of LNSP1 did not affect the average number of eggs produced from a single female but significantly reduced hatchability due, in part, to a severe level of desiccation in eggs (Fig. 3e, f ). These findings demonstrate that LNSP1 plays a critical role in preserving water in the developing egg and maintaining egg viability
Similar to the TG knockdown, administration of GGsTop, a TG inhibitor, via either hair coating or injection into gravid females, resulted in similar consequences. These findings demonstrate that TG is involved in crosslinking of LNSP1 and LNSP2

Summary

Introduction

Head louse females secrete liquid glue during oviposition, which is solidified to form the nit sheath over the egg. The insect egg is surrounded by an eggshell, a layer formed by secreted proteins and other substances from the follicle cells of oocytes [1]. The eggshell protects the egg and developing embryo from desiccation, pathogens, parasites and. The materials forming the extra egg sheath (or egg covering) are secreted from the accessory (or collateral) glands of the female’s reproductive organ. Such egg sheath can take various shapes such as a pod (e.g., cockroaches), froth case (e.g., grasshoppers and mantids) or nit sheath (e.g., human lice). The egg sheath proteins exist as liquids within the accessory gland but solidify once secreted during the egg-laying process

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