Serine proteinases of the human body louse (Pediculus humanus): sequence characterization and expression patterns

After the previous characterization of one trypsin gene (Try1) of the human body louse Pediculus humanus, genes encoding a second trypsin (Try2) and a chymotrypsin (Chy1) have been cloned using degenerate serine proteinase primers and 5¢- and 3¢-RACE, and sequenced. The deduced 259 and 267 amino acid se- quences of Try2 and Chy1 show an identity of 33%- 40% to trypsinogens and chymotrypsinogens of other insects. Considering previously published partial se- quences, P. humanus possesses at least one Try1 gene, five variants/isoforms of Try2 and six variants/isoforms of Chy1. The genomic DNA of Try2 contains three in- trons and Chy1 contains five introns. Using whole mount in situ hybridization, gene expression of Try1, Try2 and Chy1 has been localized not only in the dis- tensible anterior region of the midgut of lice but some- times also in the area following the distensible region. The Try2 gene was always expressed at much lower levels than Try1 or Chy1. This lower expression, the constitutive expression of Try1 and Chy1 at 1, 2, 6, 12 and 24 h after feeding of adults and the regional differ- ences have been verified in quantitative real-time PCR.