Identification of abundant mRNAs from the third stage larvae of the parasitic nematode, Ostertagia ostertagi

Reverse transcriptase-PCR (RT-PCR) was carried out on total RNA prepared fr om the third-stage larvae (L3) of Ostertagia ostertagi in order to clone an d characterize the major transcripts expressed in this larval stage, as an initial investigation of arrested larval development in the parasite. Disti nct bands were visible on an agarose gel and forts of these were cloned and sequenced. Three of the bands represented multiple transcripts, while the fourth band encoded the enzyme GTP cyclohydrolase I (GTP-CH), which catalys es the first and rate-limiting step in pteridine biosynthesis. Northern blo t analysis and RT-PCR demonstrated that GTP-CH is highly up-regulated in th e L3 stage and undetectable in either the L2 or adult stages. Using immunog old electron microscopy, GTP-CH was shown to be predominantly localized to the cell body of the body wall muscles and the cells of the intestine in th e L3.