Characterization of Nit Sheath Protein Functions and Transglutaminase-Mediated Crosslinking in the Human Head Louse, Pediculus Humanus Capitis

Background: Head louse females secrete liquid glue during oviposition, which is solidified to form the nit sheath over the egg. Recently, two homologous proteins, named as louse nit sheath protein (LNSP) 1 and LNSP2, 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 nit sheath and have an additional function of lubrication. Knockdown of TG also impaired egg hatching, demonstrating its role in the crosslinking of nit sheath protein. The role of TG in crosslinking was further confirmed by injecting or hair coating of GGsTop, a TG inhibitor.ConclusionBoth LNSP1 and LNSP2 are essential for maintaining egg viability besides their function as glue. The TG-mediated crosslinking plays critical roles in water preservation that are essential for ensuring normal embryogenesis. TG-mediated crosslinking 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.